Database.Persist.Class

Documentation

class (PersistEntity record, PersistEntityBackend record ~ backend, PersistCore backend) => ToBackendKey backend record where

ToBackendKey converts a PersistEntity Key into a BackendKey This can be used by each backend to convert between a Key and a plain Haskell type. For Sql, that is done with toSqlKey and fromSqlKey.

By default, a PersistEntity uses the default BackendKey for its Key and is an instance of ToBackendKey

A Key that instead uses a custom type will not be an instance of ToBackendKey.

Methods

toBackendKey :: Key record -> BackendKey backend

fromBackendKey :: BackendKey backend -> Key record

PersistStore

All the examples present here will be explained based on these schemas, datasets and functions:

schema-1

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
User
    name String
    age Int
    deriving Show
|]

dataset-1

+----+-------+-----+
| id | name  | age |
+----+-------+-----+
|  1 | SPJ   |  40 |
+----+-------+-----+
|  2 | Simon |  41 |
+----+-------+-----+

class PersistCore backend

Associated Types

data BackendKey backend

Instances

PersistCore SqlBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Associated Types

data BackendKey SqlBackend

PersistCore SqlWriteBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Associated Types

data BackendKey SqlWriteBackend

PersistCore SqlReadBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Associated Types

data BackendKey SqlReadBackend

(BackendCompatible b s, PersistCore b) => PersistCore (Compatible b s)

Defined in Database.Persist.Compatible.Types

Associated Types

data BackendKey (Compatible b s)

type PersistStore a = PersistStoreWrite a

A backwards-compatible alias for those that don't care about distinguishing between read and write queries. It signifies the assumption that, by default, a backend can write as well as read.

class (Show (BackendKey backend), Read (BackendKey backend), Eq (BackendKey backend), Ord (BackendKey backend), PersistCore backend, PersistField (BackendKey backend), ToJSON (BackendKey backend), FromJSON (BackendKey backend)) => PersistStoreRead backend where

Minimal complete definition

get

Methods

get :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Key record -> ReaderT backend m (Maybe record)

Get a record by identifier, if available.

Example usage

With schema-1 and dataset-1,

getSpj :: MonadIO m => ReaderT SqlBackend m (Maybe User)
getSpj = get spjId

mspj <- getSpj

The above query when applied on dataset-1, will get this:

+------+-----+
| name | age |
+------+-----+
| SPJ  |  40 |
+------+-----+

getMany :: forall record m. (MonadIO m, PersistRecordBackend record backend) => [Key record] -> ReaderT backend m (Map (Key record) record)

Get many records by their respective identifiers, if available.

Example usage

With schema-1 and dataset-1:

getUsers :: MonadIO m => ReaderT SqlBackend m (Map (Key User) User)
getUsers = getMany allkeys

musers <- getUsers

The above query when applied on dataset-1, will get these records:

+----+-------+-----+
| id | name  | age |
+----+-------+-----+
|  1 | SPJ   |  40 |
+----+-------+-----+
|  2 | Simon |  41 |
+----+-------+-----+

Since: 2.8.1

Instances

PersistStoreRead SqlBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

get :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Key record -> ReaderT SqlBackend m (Maybe record)

getMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => [Key record] -> ReaderT SqlBackend m (Map (Key record) record)

PersistStoreRead SqlWriteBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

get :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Key record -> ReaderT SqlWriteBackend m (Maybe record)

getMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [Key record] -> ReaderT SqlWriteBackend m (Map (Key record) record)

PersistStoreRead SqlReadBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

get :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlReadBackend) => Key record -> ReaderT SqlReadBackend m (Maybe record)

getMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlReadBackend) => [Key record] -> ReaderT SqlReadBackend m (Map (Key record) record)

(HasPersistBackend b, BackendCompatible b s, PersistStoreRead b) => PersistStoreRead (Compatible b s)

Defined in Database.Persist.Compatible.Types

Methods

get :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Key record -> ReaderT (Compatible b s) m (Maybe record)

getMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => [Key record] -> ReaderT (Compatible b s) m (Map (Key record) record)

class (Show (BackendKey backend), Read (BackendKey backend), Eq (BackendKey backend), Ord (BackendKey backend), PersistStoreRead backend, PersistField (BackendKey backend), ToJSON (BackendKey backend), FromJSON (BackendKey backend)) => PersistStoreWrite backend where

Minimal complete definition

insert, insertKey, repsert, replace, delete, update

Methods

insert :: forall record m. (MonadIO m, PersistRecordBackend record backend) => record -> ReaderT backend m (Key record)

Create a new record in the database, returning an automatically created key (in SQL an auto-increment id).

Example usage

Using schema-1 and dataset-1, let's insert a new user John.

insertJohn :: MonadIO m => ReaderT SqlBackend m (Key User)
insertJohn = insert $ User "John" 30

johnId <- insertJohn

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |John  |30   |
+-----+------+-----+

insert_ :: forall record m. (MonadIO m, PersistRecordBackend record backend) => record -> ReaderT backend m ()

Same as insert, but doesn't return a Key.

Example usage

with schema-1 and dataset-1,

insertJohn :: MonadIO m => ReaderT SqlBackend m (Key User)
insertJohn = insert_ $ User "John" 30

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |John  |30   |
+-----+------+-----+

insertMany :: forall record m. (MonadIO m, PersistRecordBackend record backend) => [record] -> ReaderT backend m [Key record]

Create multiple records in the database and return their Keys.

If you don't need the inserted Keys, use insertMany_.

The MongoDB and PostgreSQL backends insert all records and retrieve their keys in one database query.

The SQLite and MySQL backends use the slow, default implementation of mapM insert.

Example usage

with schema-1 and dataset-1,

insertUsers :: MonadIO m => ReaderT SqlBackend m [Key User]
insertUsers = insertMany [User "John" 30, User "Nick" 32, User "Jane" 20]

userIds <- insertUsers

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |John  |30   |
+-----+------+-----+
|4    |Nick  |32   |
+-----+------+-----+
|5    |Jane  |20   |
+-----+------+-----+

insertMany_ :: forall record m. (MonadIO m, PersistRecordBackend record backend) => [record] -> ReaderT backend m ()

Same as insertMany, but doesn't return any Keys.

The MongoDB, PostgreSQL, SQLite and MySQL backends insert all records in one database query.

Example usage

With schema-1 and dataset-1,

insertUsers_ :: MonadIO m => ReaderT SqlBackend m ()
insertUsers_ = insertMany_ [User "John" 30, User "Nick" 32, User "Jane" 20]

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |John  |30   |
+-----+------+-----+
|4    |Nick  |32   |
+-----+------+-----+
|5    |Jane  |20   |
+-----+------+-----+

insertEntityMany :: forall record m. (MonadIO m, PersistRecordBackend record backend) => [Entity record] -> ReaderT backend m ()

Same as insertMany_, but takes an Entity instead of just a record.

Useful when migrating data from one entity to another and want to preserve ids.

The MongoDB, PostgreSQL, SQLite and MySQL backends insert all records in one database query.

Example usage

With schema-1 and dataset-1,

insertUserEntityMany :: MonadIO m => ReaderT SqlBackend m ()
insertUserEntityMany = insertEntityMany [SnakeEntity, EvaEntity]

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |Snake |38   |
+-----+------+-----+
|4    |Eva   |38   |
+-----+------+-----+

insertKey :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Key record -> record -> ReaderT backend m ()

Create a new record in the database using the given key.

Example usage

With schema-1 and dataset-1,

insertAliceKey :: MonadIO m => Key User -> ReaderT SqlBackend m ()
insertAliceKey key = insertKey key $ User "Alice" 20

insertAliceKey $ UserKey {unUserKey = SqlBackendKey {unSqlBackendKey = 3}}

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |Alice |20   |
+-----+------+-----+

repsert :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Key record -> record -> ReaderT backend m ()

Put the record in the database with the given key. Unlike replace, if a record with the given key does not exist then a new record will be inserted.

Example usage

We try to explain upsertBy using schema-1 and dataset-1.

First, we insert Philip to dataset-1.

insertPhilip :: MonadIO m => ReaderT SqlBackend m (Key User)
insertPhilip = insert $ User "Philip" 42

philipId <- insertPhilip

This query will produce:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |Philip|42   |
+-----+------+-----+

repsertHaskell :: MonadIO m => Key record -> ReaderT SqlBackend m ()
repsertHaskell id = repsert id $ User "Haskell" 81

repsertHaskell philipId

This query will replace Philip's record with Haskell's one:

+-----+-----------------+--------+
|id   |name             |age     |
+-----+-----------------+--------+
|1    |SPJ              |40      |
+-----+-----------------+--------+
|2    |Simon            |41      |
+-----+-----------------+--------+
|3    |Philip -> Haskell|42 -> 81|
+-----+-----------------+--------+

repsert inserts the given record if the key doesn't exist.

repsertXToUnknown :: MonadIO m => ReaderT SqlBackend m ()
repsertXToUnknown = repsert unknownId $ User "X" 999

For example, applying the above query to dataset-1 will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |X     |999  |
+-----+------+-----+

repsertMany :: forall record m. (MonadIO m, PersistRecordBackend record backend) => [(Key record, record)] -> ReaderT backend m ()

Put many entities into the database.

Batch version of repsert for SQL backends.

Useful when migrating data from one entity to another and want to preserve ids.

Example usage

With schema-1 and dataset-1,

repsertManyUsers :: MonadIO m =>ReaderT SqlBackend m ()
repsertManyusers = repsertMany [(simonId, User "Philip" 20), (unknownId999, User "Mr. X" 999)]

The above query when applied on dataset-1, will produce this:

+-----+----------------+---------+
|id   |name            |age      |
+-----+----------------+---------+
|1    |SPJ             |40       |
+-----+----------------+---------+
|2    |Simon -> Philip |41 -> 20 |
+-----+----------------+---------+
|999  |Mr. X           |999      |
+-----+----------------+---------+

Since: 2.8.1

replace :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Key record -> record -> ReaderT backend m ()

Replace the record in the database with the given key. Note that the result is undefined if such record does not exist, so you must use insertKey or repsert in these cases.

Example usage

With schema-1 schama-1 and dataset-1,

replaceSpj :: MonadIO m => User -> ReaderT SqlBackend m ()
replaceSpj record = replace spjId record

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |Mike  |45   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+

delete :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Key record -> ReaderT backend m ()

Delete a specific record by identifier. Does nothing if record does not exist.

Example usage

With schema-1 and dataset-1,

deleteSpj :: MonadIO m => ReaderT SqlBackend m ()
deleteSpj = delete spjId

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+

update :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Key record -> [Update record] -> ReaderT backend m ()

Update individual fields on a specific record.

Example usage

With schema-1 and dataset-1,

updateSpj :: MonadIO m => [Update User] -> ReaderT SqlBackend m ()
updateSpj updates = update spjId updates

updateSpj [UserAge +=. 100]

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |140  |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+

updateGet :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Key record -> [Update record] -> ReaderT backend m record

Update individual fields on a specific record, and retrieve the updated value from the database.

Note that this function will throw an exception if the given key is not found in the database.

Example usage

With schema-1 and dataset-1,

updateGetSpj :: MonadIO m => [Update User] -> ReaderT SqlBackend m User
updateGetSpj updates = updateGet spjId updates

spj <- updateGetSpj [UserAge +=. 100]

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |140  |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+

Instances

PersistStoreWrite SqlBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

insert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => record -> ReaderT SqlBackend m (Key record)

insert_ :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => record -> ReaderT SqlBackend m ()

insertMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => [record] -> ReaderT SqlBackend m [Key record]

insertMany_ :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => [record] -> ReaderT SqlBackend m ()

insertEntityMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => [Entity record] -> ReaderT SqlBackend m ()

insertKey :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Key record -> record -> ReaderT SqlBackend m ()

repsert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Key record -> record -> ReaderT SqlBackend m ()

repsertMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => [(Key record, record)] -> ReaderT SqlBackend m ()

replace :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Key record -> record -> ReaderT SqlBackend m ()

delete :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Key record -> ReaderT SqlBackend m ()

update :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Key record -> [Update record] -> ReaderT SqlBackend m ()

updateGet :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Key record -> [Update record] -> ReaderT SqlBackend m record

PersistStoreWrite SqlWriteBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

insert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => record -> ReaderT SqlWriteBackend m (Key record)

insert_ :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => record -> ReaderT SqlWriteBackend m ()

insertMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [record] -> ReaderT SqlWriteBackend m [Key record]

insertMany_ :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [record] -> ReaderT SqlWriteBackend m ()

insertEntityMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [Entity record] -> ReaderT SqlWriteBackend m ()

insertKey :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Key record -> record -> ReaderT SqlWriteBackend m ()

repsert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Key record -> record -> ReaderT SqlWriteBackend m ()

repsertMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [(Key record, record)] -> ReaderT SqlWriteBackend m ()

replace :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Key record -> record -> ReaderT SqlWriteBackend m ()

delete :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Key record -> ReaderT SqlWriteBackend m ()

update :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Key record -> [Update record] -> ReaderT SqlWriteBackend m ()

updateGet :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Key record -> [Update record] -> ReaderT SqlWriteBackend m record

(HasPersistBackend b, BackendCompatible b s, PersistStoreWrite b) => PersistStoreWrite (Compatible b s)

Defined in Database.Persist.Compatible.Types

Methods

insert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => record -> ReaderT (Compatible b s) m (Key record)

insert_ :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => record -> ReaderT (Compatible b s) m ()

insertMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => [record] -> ReaderT (Compatible b s) m [Key record]

insertMany_ :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => [record] -> ReaderT (Compatible b s) m ()

insertEntityMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => [Entity record] -> ReaderT (Compatible b s) m ()

insertKey :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Key record -> record -> ReaderT (Compatible b s) m ()

repsert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Key record -> record -> ReaderT (Compatible b s) m ()

repsertMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => [(Key record, record)] -> ReaderT (Compatible b s) m ()

replace :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Key record -> record -> ReaderT (Compatible b s) m ()

delete :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Key record -> ReaderT (Compatible b s) m ()

update :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Key record -> [Update record] -> ReaderT (Compatible b s) m ()

updateGet :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Key record -> [Update record] -> ReaderT (Compatible b s) m record

type PersistRecordBackend record backend = (PersistEntity record, PersistEntityBackend record ~ BaseBackend backend)

A convenient alias for common type signatures

getJust :: forall record backend m. (PersistStoreRead backend, PersistRecordBackend record backend, MonadIO m) => Key record -> ReaderT backend m record

Same as get, but for a non-null (not Maybe) foreign key. Unsafe unless your database is enforcing that the foreign key is valid.

Example usage

With schema-1 and dataset-1,

getJustSpj :: MonadIO m => ReaderT SqlBackend m User
getJustSpj = getJust spjId

spj <- getJust spjId

The above query when applied on dataset-1, will get this record:

+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | SPJ  |  40 |
+----+------+-----+

getJustUnknown :: MonadIO m => ReaderT SqlBackend m User
getJustUnknown = getJust unknownId

mrx <- getJustUnknown

This just throws an error.

getJustEntity :: forall record backend m. (PersistEntityBackend record ~ BaseBackend backend, MonadIO m, PersistEntity record, PersistStoreRead backend) => Key record -> ReaderT backend m (Entity record)

Same as getJust, but returns an Entity instead of just the record.

Example usage

With schema-1 and dataset-1,

getJustEntitySpj :: MonadIO m => ReaderT SqlBackend m (Entity User)
getJustEntitySpj = getJustEntity spjId

spjEnt <- getJustEntitySpj

The above query when applied on dataset-1, will get this entity:

+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | SPJ  |  40 |
+----+------+-----+

Since: 2.6.1

getEntity :: forall e backend m. (PersistStoreRead backend, PersistRecordBackend e backend, MonadIO m) => Key e -> ReaderT backend m (Maybe (Entity e))

Like get, but returns the complete Entity.

Example usage

With schema-1 and dataset-1,

getSpjEntity :: MonadIO m => ReaderT SqlBackend m (Maybe (Entity User))
getSpjEntity = getEntity spjId

mSpjEnt <- getSpjEntity

The above query when applied on dataset-1, will get this entity:

+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | SPJ  |  40 |
+----+------+-----+

belongsTo :: forall ent1 ent2 backend m. (PersistStoreRead backend, PersistEntity ent1, PersistRecordBackend ent2 backend, MonadIO m) => (ent1 -> Maybe (Key ent2)) -> ent1 -> ReaderT backend m (Maybe ent2)

Curry this to make a convenience function that loads an associated model.

foreign = belongsTo foreignId

belongsToJust :: forall ent1 ent2 backend m. (PersistStoreRead backend, PersistEntity ent1, PersistRecordBackend ent2 backend, MonadIO m) => (ent1 -> Key ent2) -> ent1 -> ReaderT backend m ent2

Same as belongsTo, but uses getJust and therefore is similarly unsafe.

insertEntity :: forall e backend m. (PersistStoreWrite backend, PersistRecordBackend e backend, MonadIO m) => e -> ReaderT backend m (Entity e)

Like insert, but returns the complete Entity.

Example usage

With schema-1 and dataset-1,

insertHaskellEntity :: MonadIO m => ReaderT SqlBackend m (Entity User)
insertHaskellEntity = insertEntity $ User "Haskell" 81

haskellEnt <- insertHaskellEntity

The above query when applied on dataset-1, will produce this:

+----+---------+-----+
| id |  name   | age |
+----+---------+-----+
|  1 | SPJ     |  40 |
+----+---------+-----+
|  2 | Simon   |  41 |
+----+---------+-----+
|  3 | Haskell |  81 |
+----+---------+-----+

insertRecord :: forall record backend m. (PersistEntityBackend record ~ BaseBackend backend, PersistEntity record, MonadIO m, PersistStoreWrite backend) => record -> ReaderT backend m record

Like insertEntity but just returns the record instead of Entity.

Example usage

With schema-1 and dataset-1,

insertDaveRecord :: MonadIO m => ReaderT SqlBackend m User
insertDaveRecord = insertRecord $ User "Dave" 50

dave <- insertDaveRecord

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |Dave  |50   |
+-----+------+-----+

Since: 2.6.1

PersistUnique

All the examples present here will be explained based on these two schemas and the dataset:

schema-1

This schema has single unique constraint.

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
User
    name String
    age Int
    UniqueUserName name
    deriving Show
|]

schema-2

This schema has two unique constraints.

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
User
    name String
    age Int
    UniqueUserName name
    UniqueUserAge age
    deriving Show
|]

dataset-1

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+
|2    |Simon|41   |
+-----+-----+-----+

type PersistUnique a = PersistUniqueWrite a

A backwards-compatible alias for those that don't care about distinguishing between read and write queries. It signifies the assumption that, by default, a backend can write as well as read.

class PersistStoreRead backend => PersistUniqueRead backend where

Queries against Unique keys (other than the id Key).

Please read the general Persistent documentation to learn how to create Unique keys.

Using this with an Entity without a Unique key leads to undefined behavior. A few of these functions require a single Unique, so using an Entity with multiple Uniques is also undefined. In these cases persistent's goal is to throw an exception as soon as possible, but persistent is still transitioning to that.

SQL backends automatically create uniqueness constraints, but for MongoDB you must manually place a unique index on a field to have a uniqueness constraint.

Methods

getBy :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Unique record -> ReaderT backend m (Maybe (Entity record))

Get a record by unique key, if available. Returns also the identifier.

Example usage

With schema-1 and dataset-1:

getBySpjName :: MonadIO m  => ReaderT SqlBackend m (Maybe (Entity User))
getBySpjName = getBy $ UniqueUserName "SPJ"

mSpjEnt <- getBySpjName

The above query when applied on dataset-1, will get this entity:

+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | SPJ  |  40 |
+----+------+-----+

Instances

PersistUniqueRead SqlBackend

Defined in Database.Persist.Sql.Orphan.PersistUnique

Methods

getBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Unique record -> ReaderT SqlBackend m (Maybe (Entity record))

PersistUniqueRead SqlWriteBackend

Defined in Database.Persist.Sql.Orphan.PersistUnique

Methods

getBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Unique record -> ReaderT SqlWriteBackend m (Maybe (Entity record))

PersistUniqueRead SqlReadBackend

Defined in Database.Persist.Sql.Orphan.PersistUnique

Methods

getBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlReadBackend) => Unique record -> ReaderT SqlReadBackend m (Maybe (Entity record))

(HasPersistBackend b, BackendCompatible b s, PersistUniqueRead b) => PersistUniqueRead (Compatible b s)

Defined in Database.Persist.Compatible.Types

Methods

getBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Unique record -> ReaderT (Compatible b s) m (Maybe (Entity record))

class (PersistUniqueRead backend, PersistStoreWrite backend) => PersistUniqueWrite backend where

Some functions in this module (insertUnique, insertBy, and replaceUnique) first query the unique indexes to check for conflicts. You could instead optimistically attempt to perform the operation (e.g. replace instead of replaceUnique). However,

• there is some fragility to trying to catch the correct exception and determing the column of failure;
• an exception will automatically abort the current SQL transaction.

Minimal complete definition

deleteBy

Methods

deleteBy :: forall record m. (MonadIO m, PersistRecordBackend record backend) => Unique record -> ReaderT backend m ()

Delete a specific record by unique key. Does nothing if no record matches.

Example usage

With schema-1 and dataset-1,

deleteBySpjName :: MonadIO m => ReaderT SqlBackend m ()
deleteBySpjName = deleteBy UniqueUserName "SPJ"

The above query when applied on dataset-1, will produce this:

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+

insertUnique :: forall record m. (MonadIO m, PersistRecordBackend record backend) => record -> ReaderT backend m (Maybe (Key record))

Like insert, but returns Nothing when the record couldn't be inserted because of a uniqueness constraint.

Example usage

With schema-1 and dataset-1, we try to insert the following two records:

linusId <- insertUnique $ User "Linus" 48
spjId   <- insertUnique $ User "SPJ" 90

+-----+------+-----+
|id   |name  |age  |
+-----+------+-----+
|1    |SPJ   |40   |
+-----+------+-----+
|2    |Simon |41   |
+-----+------+-----+
|3    |Linus |48   |
+-----+------+-----+

Linus's record was inserted to dataset-1, while SPJ wasn't because SPJ already exists in dataset-1.

upsert

Arguments

:: forall record m. (MonadIO m, PersistRecordBackend record backend, OnlyOneUniqueKey record)

=> record

new record to insert

-> [Update record]

updates to perform if the record already exists

-> ReaderT backend m (Entity record)

the record in the database after the operation

Update based on a uniqueness constraint or insert:

• insert the new record if it does not exist;
• If the record exists (matched via it's uniqueness constraint), then update the existing record with the parameters which is passed on as list to the function.

Example usage

First, we try to explain upsert using schema-1 and dataset-1.

upsertSpj :: MonadIO m => [Update User] -> ReaderT SqlBackend m (Maybe (Entity User))
upsertSpj updates = upsert (User "SPJ" 999) upadtes

mSpjEnt <- upsertSpj [UserAge +=. 15]

The above query when applied on dataset-1, will produce this:

+-----+-----+--------+
|id   |name |age     |
+-----+-----+--------+
|1    |SPJ  |40 -> 55|
+-----+-----+--------+
|2    |Simon|41      |
+-----+-----+--------+

upsertX :: MonadIO m => [Update User] -> ReaderT SqlBackend m (Maybe (Entity User))
upsertX updates = upsert (User "X" 999) updates

mXEnt <- upsertX [UserAge +=. 15]

The above query when applied on dataset-1, will produce this:

+-----+-----+--------+
|id   |name |age     |
+-----+-----+--------+
|1    |SPJ  |40      |
+-----+-----+--------+
|2    |Simon|41      |
+-----+-----+--------+
|3    |X    |999     |
+-----+-----+--------+

Next, what if the schema has two uniqueness constraints? Let's check it out using schema-2:

mSpjEnt <- upsertSpj [UserAge +=. 15]

This fails with a compile-time type error alerting us to the fact that this record has multiple unique keys, and suggests that we look for upsertBy to select the unique key we want.

upsertBy

Arguments

:: forall record m. (MonadIO m, PersistRecordBackend record backend)

=> Unique record

uniqueness constraint to find by

-> record

new record to insert

-> [Update record]

updates to perform if the record already exists

-> ReaderT backend m (Entity record)

the record in the database after the operation

Update based on a given uniqueness constraint or insert:

• insert the new record if it does not exist;
• update the existing record that matches the given uniqueness constraint.

Example usage

We try to explain upsertBy using schema-2 and dataset-1.

upsertBySpjName :: MonadIO m => User -> [Update User] -> ReaderT SqlBackend m (Entity User)
upsertBySpjName record updates = upsertBy (UniqueUserName "SPJ") record updates

mSpjEnt <- upsertBySpjName (Person "X" 999) [PersonAge += .15]

The above query will alter dataset-1 to:

+-----+-----+--------+
|id   |name |age     |
+-----+-----+--------+
|1    |SPJ  |40 -> 55|
+-----+-----+--------+
|2    |Simon|41      |
+-----+-----+--------+

upsertBySimonAge :: MonadIO m => User -> [Update User] -> ReaderT SqlBackend m (Entity User)
upsertBySimonAge record updates = upsertBy (UniqueUserName "SPJ") record updates

mPhilipEnt <- upsertBySimonAge (User "X" 999) [UserName =. "Philip"]

The above query will alter dataset-1 to:

+----+-----------------+-----+
| id |      name       | age |
+----+-----------------+-----+
|  1 | SPJ             |  40 |
+----+-----------------+-----+
|  2 | Simon -> Philip |  41 |
+----+-----------------+-----+

upsertByUnknownName :: MonadIO m => User -> [Update User] -> ReaderT SqlBackend m (Entity User)
upsertByUnknownName record updates = upsertBy (UniqueUserName "Unknown") record updates

mXEnt <- upsertByUnknownName (User "X" 999) [UserAge +=. 15]

This query will alter dataset-1 to:

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+
|2    |Simon|41   |
+-----+-----+-----+
|3    |X    |999  |
+-----+-----+-----+

putMany

Arguments

:: forall record m. (MonadIO m, PersistRecordBackend record backend)

=> [record]

A list of the records you want to insert or replace.

-> ReaderT backend m ()

Put many records into db

• insert new records that do not exist (or violate any unique constraints)
• replace existing records (matching any unique constraint)

Since: 2.8.1

Instances

PersistUniqueWrite SqlBackend

Defined in Database.Persist.Sql.Orphan.PersistUnique

Methods

deleteBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Unique record -> ReaderT SqlBackend m ()

insertUnique :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => record -> ReaderT SqlBackend m (Maybe (Key record))

upsert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend, OnlyOneUniqueKey record) => record -> [Update record] -> ReaderT SqlBackend m (Entity record)

upsertBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => Unique record -> record -> [Update record] -> ReaderT SqlBackend m (Entity record)

putMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlBackend) => [record] -> ReaderT SqlBackend m ()

PersistUniqueWrite SqlWriteBackend

Defined in Database.Persist.Sql.Orphan.PersistUnique

Methods

deleteBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Unique record -> ReaderT SqlWriteBackend m ()

insertUnique :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => record -> ReaderT SqlWriteBackend m (Maybe (Key record))

upsert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend, OnlyOneUniqueKey record) => record -> [Update record] -> ReaderT SqlWriteBackend m (Entity record)

upsertBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => Unique record -> record -> [Update record] -> ReaderT SqlWriteBackend m (Entity record)

putMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [record] -> ReaderT SqlWriteBackend m ()

(HasPersistBackend b, BackendCompatible b s, PersistUniqueWrite b) => PersistUniqueWrite (Compatible b s)

Defined in Database.Persist.Compatible.Types

Methods

deleteBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Unique record -> ReaderT (Compatible b s) m ()

insertUnique :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => record -> ReaderT (Compatible b s) m (Maybe (Key record))

upsert :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s), OnlyOneUniqueKey record) => record -> [Update record] -> ReaderT (Compatible b s) m (Entity record)

upsertBy :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => Unique record -> record -> [Update record] -> ReaderT (Compatible b s) m (Entity record)

putMany :: forall record (m :: Type -> Type). (MonadIO m, PersistRecordBackend record (Compatible b s)) => [record] -> ReaderT (Compatible b s) m ()

class PersistEntity record => OnlyOneUniqueKey record where

This class is used to ensure that upsert is only called on records that have a single Unique key. The quasiquoter automatically generates working instances for appropriate records, and generates TypeError instances for records that have 0 or multiple unique keys.

Since: 2.10.0

Methods

onlyUniqueP :: record -> Unique record

class PersistEntity record => AtLeastOneUniqueKey record where

This class is used to ensure that functions requring at least one unique key are not called with records that have 0 unique keys. The quasiquoter automatically writes working instances for appropriate entities, and generates TypeError instances for records that have 0 unique keys.

Since: 2.10.0

Methods

requireUniquesP :: record -> NonEmpty (Unique record)

onlyOneUniqueDef :: (OnlyOneUniqueKey record, Monad proxy) => proxy record -> UniqueDef

Given a proxy for a PersistEntity record, this returns the sole UniqueDef for that entity.

Since: 2.13.0.0

type NoUniqueKeysError ty = (('Text "The entity " :<>: 'ShowType ty) :<>: 'Text " does not have any unique keys.") :$$: ('Text "The function you are trying to call requires a unique key " :<>: 'Text "to be defined on the entity.")

This is an error message. It is used when writing instances of OnlyOneUniqueKey for an entity that has no unique keys.

Since: 2.10.0

type MultipleUniqueKeysError ty = ((('Text "The entity " :<>: 'ShowType ty) :<>: 'Text " has multiple unique keys.") :$$: ('Text "The function you are trying to call requires only a single " :<>: 'Text "unique key.")) :$$: (('Text "There is probably a variant of the function with 'By' " :<>: 'Text "appended that will allow you to select a unique key ") :<>: 'Text "for the operation.")

This is an error message. It is used when an entity has multiple unique keys, and the function expects a single unique key.

Since: 2.10.0

getByValue :: forall record m backend. (MonadIO m, PersistUniqueRead backend, PersistRecordBackend record backend, AtLeastOneUniqueKey record) => record -> ReaderT backend m (Maybe (Entity record))

A modification of getBy, which takes the PersistEntity itself instead of a Unique record. Returns a record matching one of the unique keys. This function makes the most sense on entities with a single Unique constructor.

Example usage

With schema-1 and dataset-1,

getBySpjValue :: MonadIO m => ReaderT SqlBackend m (Maybe (Entity User)) getBySpjValue = getByValue $ User SPJ 999

mSpjEnt <- getBySpjValue

The above query when applied on dataset-1, will get this record:

+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | SPJ  |  40 |
+----+------+-----+

insertBy :: forall record backend m. (MonadIO m, PersistUniqueWrite backend, PersistRecordBackend record backend, AtLeastOneUniqueKey record) => record -> ReaderT backend m (Either (Entity record) (Key record))

Insert a value, checking for conflicts with any unique constraints. If a duplicate exists in the database, it is returned as Left. Otherwise, the new 'Key is returned as Right.

Example usage

With schema-2 and dataset-1, we have following lines of code:

l1 <- insertBy $ User "SPJ" 20
l2 <- insertBy $ User "XXX" 41
l3 <- insertBy $ User "SPJ" 40
r1 <- insertBy $ User "XXX" 100

First three lines return Left because there're duplicates in given record's uniqueness constraints. While the last line returns a new key as Right.

insertUniqueEntity :: forall record backend m. (MonadIO m, PersistRecordBackend record backend, PersistUniqueWrite backend) => record -> ReaderT backend m (Maybe (Entity record))

Like insertEntity, but returns Nothing when the record couldn't be inserted because of a uniqueness constraint.

Example usage

We use schema-2 and dataset-1 here.

insertUniqueSpjEntity :: MonadIO m => ReaderT SqlBackend m (Maybe (Entity User))
insertUniqueSpjEntity = insertUniqueEntity $ User "SPJ" 50

mSpjEnt <- insertUniqueSpjEntity

The above query results Nothing as SPJ already exists.

insertUniqueAlexaEntity :: MonadIO m => ReaderT SqlBackend m (Maybe (Entity User))
insertUniqueAlexaEntity = insertUniqueEntity $ User "Alexa" 3

mAlexaEnt <- insertUniqueSpjEntity

Because there's no such unique keywords of the given record, the above query when applied on dataset-1, will produce this:

+----+-------+-----+
| id | name  | age |
+----+-------+-----+
|  1 | SPJ   |  40 |
+----+-------+-----+
|  2 | Simon |  41 |
+----+-------+-----+
|  3 | Alexa |   3 |
+----+-------+-----+

Since: 2.7.1

replaceUnique :: forall record backend m. (MonadIO m, Eq (Unique record), PersistRecordBackend record backend, PersistUniqueWrite backend) => Key record -> record -> ReaderT backend m (Maybe (Unique record))

Attempt to replace the record of the given key with the given new record. First query the unique fields to make sure the replacement maintains uniqueness constraints.

Return Nothing if the replacement was made. If uniqueness is violated, return a Just with the Unique violation

Since: 1.2.2.0

checkUnique :: forall record backend m. (MonadIO m, PersistRecordBackend record backend, PersistUniqueRead backend) => record -> ReaderT backend m (Maybe (Unique record))

Check whether there are any conflicts for unique keys with this entity and existing entities in the database.

Returns Nothing if the entity would be unique, and could thus safely be inserted. on a conflict returns the conflicting key

Example usage

We use schema-1 and dataset-1 here.

This would be Nothing:

mAlanConst <- checkUnique $ User "Alan" 70

While this would be Just because SPJ already exists:

mSpjConst <- checkUnique $ User "SPJ" 60

checkUniqueUpdateable :: forall record backend m. (MonadIO m, PersistRecordBackend record backend, PersistUniqueRead backend) => Entity record -> ReaderT backend m (Maybe (Unique record))

Check whether there are any conflicts for unique keys with this entity and existing entities in the database.

Returns Nothing if the entity would stay unique, and could thus safely be updated. on a conflict returns the conflicting key

This is similar to checkUnique, except it's useful for updating - when the particular entity already exists, it would normally conflict with itself. This variant ignores those conflicts

Example usage

We use schema-1 and dataset-1 here.

This would be Nothing:

mAlanConst <- checkUnique $ User "Alan" 70

While this would be Just because SPJ already exists:

mSpjConst <- checkUnique $ User "SPJ" 60

Since: 2.11.0.0

onlyUnique :: forall record backend m. (MonadIO m, PersistUniqueWrite backend, PersistRecordBackend record backend, OnlyOneUniqueKey record) => record -> ReaderT backend m (Unique record)

Return the single unique key for a record.

Example usage

We use shcema-1 and dataset-1 here.

onlySimonConst :: MonadIO m => ReaderT SqlBackend m (Unique User)
onlySimonConst = onlyUnique $ User "Simon" 999

mSimonConst <- onlySimonConst

mSimonConst would be Simon's uniqueness constraint. Note that onlyUnique doesn't work if there're more than two constraints. It will fail with a type error instead.

PersistQuery

type PersistQuery a = PersistQueryWrite a

A backwards-compatible alias for those that don't care about distinguishing between read and write queries. It signifies the assumption that, by default, a backend can write as well as read.

class (PersistCore backend, PersistStoreRead backend) => PersistQueryRead backend where

Backends supporting conditional read operations.

Minimal complete definition

selectSourceRes, selectKeysRes, count, exists

Methods

selectSourceRes :: (PersistRecordBackend record backend, MonadIO m1, MonadIO m2) => [Filter record] -> [SelectOpt record] -> ReaderT backend m1 (Acquire (ConduitM () (Entity record) m2 ()))

Get all records matching the given criterion in the specified order. Returns also the identifiers.

selectFirst :: (MonadIO m, PersistRecordBackend record backend) => [Filter record] -> [SelectOpt record] -> ReaderT backend m (Maybe (Entity record))

Get just the first record for the criterion.

selectKeysRes :: (MonadIO m1, MonadIO m2, PersistRecordBackend record backend) => [Filter record] -> [SelectOpt record] -> ReaderT backend m1 (Acquire (ConduitM () (Key record) m2 ()))

Get the Keys of all records matching the given criterion.

count :: (MonadIO m, PersistRecordBackend record backend) => [Filter record] -> ReaderT backend m Int

The total number of records fulfilling the given criterion.

exists :: (MonadIO m, PersistRecordBackend record backend) => [Filter record] -> ReaderT backend m Bool

Check if there is at least one record fulfilling the given criterion.

Since: 2.11

Instances

PersistQueryRead SqlBackend

Defined in Database.Persist.Sql.Orphan.PersistQuery

Methods

selectSourceRes :: forall record (m1 :: Type -> Type) (m2 :: Type -> Type). (PersistRecordBackend record SqlBackend, MonadIO m1, MonadIO m2) => [Filter record] -> [SelectOpt record] -> ReaderT SqlBackend m1 (Acquire (ConduitM () (Entity record) m2 ()))

selectFirst :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlBackend) => [Filter record] -> [SelectOpt record] -> ReaderT SqlBackend m (Maybe (Entity record))

selectKeysRes :: forall (m1 :: Type -> Type) (m2 :: Type -> Type) record. (MonadIO m1, MonadIO m2, PersistRecordBackend record SqlBackend) => [Filter record] -> [SelectOpt record] -> ReaderT SqlBackend m1 (Acquire (ConduitM () (Key record) m2 ()))

count :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlBackend) => [Filter record] -> ReaderT SqlBackend m Int

exists :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlBackend) => [Filter record] -> ReaderT SqlBackend m Bool

PersistQueryRead SqlWriteBackend

Defined in Database.Persist.Sql.Orphan.PersistQuery

Methods

selectSourceRes :: forall record (m1 :: Type -> Type) (m2 :: Type -> Type). (PersistRecordBackend record SqlWriteBackend, MonadIO m1, MonadIO m2) => [Filter record] -> [SelectOpt record] -> ReaderT SqlWriteBackend m1 (Acquire (ConduitM () (Entity record) m2 ()))

selectFirst :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [Filter record] -> [SelectOpt record] -> ReaderT SqlWriteBackend m (Maybe (Entity record))

selectKeysRes :: forall (m1 :: Type -> Type) (m2 :: Type -> Type) record. (MonadIO m1, MonadIO m2, PersistRecordBackend record SqlWriteBackend) => [Filter record] -> [SelectOpt record] -> ReaderT SqlWriteBackend m1 (Acquire (ConduitM () (Key record) m2 ()))

count :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [Filter record] -> ReaderT SqlWriteBackend m Int

exists :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [Filter record] -> ReaderT SqlWriteBackend m Bool

PersistQueryRead SqlReadBackend

Defined in Database.Persist.Sql.Orphan.PersistQuery

Methods

selectSourceRes :: forall record (m1 :: Type -> Type) (m2 :: Type -> Type). (PersistRecordBackend record SqlReadBackend, MonadIO m1, MonadIO m2) => [Filter record] -> [SelectOpt record] -> ReaderT SqlReadBackend m1 (Acquire (ConduitM () (Entity record) m2 ()))

selectFirst :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlReadBackend) => [Filter record] -> [SelectOpt record] -> ReaderT SqlReadBackend m (Maybe (Entity record))

selectKeysRes :: forall (m1 :: Type -> Type) (m2 :: Type -> Type) record. (MonadIO m1, MonadIO m2, PersistRecordBackend record SqlReadBackend) => [Filter record] -> [SelectOpt record] -> ReaderT SqlReadBackend m1 (Acquire (ConduitM () (Key record) m2 ()))

count :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlReadBackend) => [Filter record] -> ReaderT SqlReadBackend m Int

exists :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlReadBackend) => [Filter record] -> ReaderT SqlReadBackend m Bool

(HasPersistBackend b, BackendCompatible b s, PersistQueryRead b) => PersistQueryRead (Compatible b s)

Defined in Database.Persist.Compatible.Types

Methods

selectSourceRes :: forall record (m1 :: Type -> Type) (m2 :: Type -> Type). (PersistRecordBackend record (Compatible b s), MonadIO m1, MonadIO m2) => [Filter record] -> [SelectOpt record] -> ReaderT (Compatible b s) m1 (Acquire (ConduitM () (Entity record) m2 ()))

selectFirst :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record (Compatible b s)) => [Filter record] -> [SelectOpt record] -> ReaderT (Compatible b s) m (Maybe (Entity record))

selectKeysRes :: forall (m1 :: Type -> Type) (m2 :: Type -> Type) record. (MonadIO m1, MonadIO m2, PersistRecordBackend record (Compatible b s)) => [Filter record] -> [SelectOpt record] -> ReaderT (Compatible b s) m1 (Acquire (ConduitM () (Key record) m2 ()))

count :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record (Compatible b s)) => [Filter record] -> ReaderT (Compatible b s) m Int

exists :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record (Compatible b s)) => [Filter record] -> ReaderT (Compatible b s) m Bool

class (PersistQueryRead backend, PersistStoreWrite backend) => PersistQueryWrite backend where

Backends supporting conditional write operations

Methods

updateWhere :: (MonadIO m, PersistRecordBackend record backend) => [Filter record] -> [Update record] -> ReaderT backend m ()

Update individual fields on any record matching the given criterion.

deleteWhere :: (MonadIO m, PersistRecordBackend record backend) => [Filter record] -> ReaderT backend m ()

Delete all records matching the given criterion.

Instances

PersistQueryWrite SqlBackend

Defined in Database.Persist.Sql.Orphan.PersistQuery

Methods

updateWhere :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlBackend) => [Filter record] -> [Update record] -> ReaderT SqlBackend m ()

deleteWhere :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlBackend) => [Filter record] -> ReaderT SqlBackend m ()

PersistQueryWrite SqlWriteBackend

Defined in Database.Persist.Sql.Orphan.PersistQuery

Methods

updateWhere :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [Filter record] -> [Update record] -> ReaderT SqlWriteBackend m ()

deleteWhere :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record SqlWriteBackend) => [Filter record] -> ReaderT SqlWriteBackend m ()

(HasPersistBackend b, BackendCompatible b s, PersistQueryWrite b) => PersistQueryWrite (Compatible b s)

Defined in Database.Persist.Compatible.Types

Methods

updateWhere :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record (Compatible b s)) => [Filter record] -> [Update record] -> ReaderT (Compatible b s) m ()

deleteWhere :: forall (m :: Type -> Type) record. (MonadIO m, PersistRecordBackend record (Compatible b s)) => [Filter record] -> ReaderT (Compatible b s) m ()

selectSource :: forall record backend m. (PersistQueryRead backend, MonadResource m, PersistRecordBackend record backend, MonadReader backend m) => [Filter record] -> [SelectOpt record] -> ConduitM () (Entity record) m ()

Get all records matching the given criterion in the specified order. Returns also the identifiers.

selectKeys :: forall record backend m. (PersistQueryRead backend, MonadResource m, PersistRecordBackend record backend, MonadReader backend m) => [Filter record] -> [SelectOpt record] -> ConduitM () (Key record) m ()

Get the Keys of all records matching the given criterion.

selectList :: forall record backend m. (MonadIO m, PersistQueryRead backend, PersistRecordBackend record backend) => [Filter record] -> [SelectOpt record] -> ReaderT backend m [Entity record]

Call selectSource but return the result as a list.

selectKeysList :: forall record backend m. (MonadIO m, PersistQueryRead backend, PersistRecordBackend record backend) => [Filter record] -> [SelectOpt record] -> ReaderT backend m [Key record]

Call selectKeys but return the result as a list.

DeleteCascade

class (PersistStoreWrite backend, PersistEntity record, BaseBackend backend ~ PersistEntityBackend record) => DeleteCascade record backend where

For combinations of backends and entities that support cascade-deletion. “Cascade-deletion” means that entries that depend on other entries to be deleted will be deleted as well.

Methods

deleteCascade :: MonadIO m => Key record -> ReaderT backend m ()

Perform cascade-deletion of single database entry.

deleteCascadeWhere :: forall record backend m. (MonadIO m, DeleteCascade record backend, PersistQueryWrite backend) => [Filter record] -> ReaderT backend m ()

Cascade-deletion of entries satisfying given filters.

PersistEntity

class (PersistField (Key record), ToJSON (Key record), FromJSON (Key record), Show (Key record), Read (Key record), Eq (Key record), Ord (Key record)) => PersistEntity record where

Persistent serialized Haskell records to the database. A Database Entity (A row in SQL, a document in MongoDB, etc) corresponds to a Key plus a Haskell record.

For every Haskell record type stored in the database there is a corresponding PersistEntity instance. An instance of PersistEntity contains meta-data for the record. PersistEntity also helps abstract over different record types. That way the same query interface can return a PersistEntity, with each query returning different types of Haskell records.

Some advanced type system capabilities are used to make this process type-safe. Persistent users usually don't need to understand the class associated data and functions.

Minimal complete definition

keyToValues, keyFromValues, persistIdField, entityDef, persistFieldDef, toPersistFields, fromPersistValues, persistUniqueKeys, persistUniqueToFieldNames, persistUniqueToValues, fieldLens

Associated Types

type PersistEntityBackend record

Persistent allows multiple different backends (databases).

data Key record

By default, a backend will automatically generate the key Instead you can specify a Primary key made up of unique values.

data EntityField record :: * -> *

An EntityField is parameterised by the Haskell record it belongs to and the additional type of that field.

As of persistent-2.11.0.0, it's possible to use the OverloadedLabels language extension to refer to EntityField values polymorphically. See the documentation on SymbolToField for more information.

data Unique record

Unique keys besides the Key.

Methods

keyToValues :: Key record -> [PersistValue]

A lower-level key operation.

keyFromValues :: [PersistValue] -> Either Text (Key record)

A lower-level key operation.

persistIdField :: EntityField record (Key record)

A meta-operation to retrieve the Key EntityField.

entityDef :: proxy record -> EntityDef

Retrieve the EntityDef meta-data for the record.

persistFieldDef :: EntityField record typ -> FieldDef

Return meta-data for a given EntityField.

toPersistFields :: record -> [SomePersistField]

A meta-operation to get the database fields of a record.

fromPersistValues :: [PersistValue] -> Either Text record

A lower-level operation to convert from database values to a Haskell record.

persistUniqueKeys :: record -> [Unique record]

A meta operation to retrieve all the Unique keys.

persistUniqueToFieldNames :: Unique record -> NonEmpty (FieldNameHS, FieldNameDB)

A lower level operation.

persistUniqueToValues :: Unique record -> [PersistValue]

A lower level operation.

fieldLens :: EntityField record field -> forall f. Functor f => (field -> f field) -> Entity record -> f (Entity record)

Use a PersistField as a lens.

keyFromRecordM :: Maybe (record -> Key record)

Extract a Key record from a record value. Currently, this is only defined for entities using the Primary syntax for natural/composite keys. In a future version of persistent which incorporates the ID directly into the entity, this will always be Just.

Since: 2.11.0.0

class SymbolToField (sym :: Symbol) rec typ | sym rec -> typ where

This type class is used with the OverloadedLabels extension to provide a more convenient means of using the EntityField type. EntityField definitions are prefixed with the type name to avoid ambiguity, but this ambiguity can result in verbose code.

If you have a table User with a name Text field, then the corresponding EntityField is UserName. With this, we can write #name :: EntityField User Text.

What's more fun is that the type is more general: it's actually #name :: (SymbolToField "name" rec typ) => EntityField rec typ

Which means it is *polymorphic* over the actual record. This allows you to write code that can be generic over the tables, provided they have the right fields.

Since: 2.11.0.0

Methods

symbolToField :: EntityField rec typ

PersistField

class PersistField a where

This class teaches Persistent how to take a custom type and marshal it to and from a PersistValue, allowing it to be stored in a database.

Examples

Simple Newtype

You can use newtype to add more type safety/readability to a basis type like ByteString. In these cases, just derive PersistField and PersistFieldSql:

{-# LANGUAGE GeneralizedNewtypeDeriving #-}

newtype HashedPassword = HashedPassword ByteString
  deriving (Eq, Show, PersistField, PersistFieldSql)

Smart Constructor Newtype

In this example, we create a PersistField instance for a newtype following the "Smart Constructor" pattern.

{-# LANGUAGE GeneralizedNewtypeDeriving #-}
import qualified Data.Text as T
import qualified Data.Char as C

-- | An American Social Security Number
newtype SSN = SSN Text
 deriving (Eq, Show, PersistFieldSql)

mkSSN :: Text -> Either Text SSN
mkSSN t = if (T.length t == 9) && (T.all C.isDigit t)
 then Right $ SSN t
 else Left $ "Invalid SSN: " <> t

instance PersistField SSN where
  toPersistValue (SSN t) = PersistText t
  fromPersistValue (PersistText t) = mkSSN t
  -- Handle cases where the database does not give us PersistText
  fromPersistValue x = Left $ "File.hs: When trying to deserialize an SSN: expected PersistText, received: " <> T.pack (show x)

Tips:

• This file contain dozens of PersistField instances you can look at for examples.
• Typically custom PersistField instances will only accept a single PersistValue constructor in fromPersistValue.
• Internal PersistField instances accept a wide variety of PersistValues to accomodate e.g. storing booleans as integers, booleans or strings.
• If you're making a custom instance and using a SQL database, you'll also need PersistFieldSql to specify the type of the database column.

Methods

toPersistValue :: a -> PersistValue

fromPersistValue :: PersistValue -> Either Text a

Instances

PersistField Bool

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Bool -> PersistValue

fromPersistValue :: PersistValue -> Either Text Bool

PersistField Double

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Double -> PersistValue

fromPersistValue :: PersistValue -> Either Text Double

PersistField Int

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Int -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int

PersistField Int8

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Int8 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int8

PersistField Int16

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Int16 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int16

PersistField Int32

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Int32 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int32

PersistField Int64

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Int64 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int64

(TypeError ((((('Text "The instance of PersistField for the Natural type was removed." :$$: 'Text "Please see the documentation for OverflowNatural if you want to ") :$$: 'Text "continue using the old behavior or want to see documentation on ") :$$: 'Text "why the instance was removed.") :$$: 'Text "") :$$: 'Text "This error instance will be removed in a future release.") :: Constraint) => PersistField Natural

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Natural -> PersistValue

fromPersistValue :: PersistValue -> Either Text Natural

PersistField Rational

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Rational -> PersistValue

fromPersistValue :: PersistValue -> Either Text Rational

PersistField Word

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Word -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word

PersistField Word8

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Word8 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word8

PersistField Word16

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Word16 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word16

PersistField Word32

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Word32 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word32

PersistField Word64

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Word64 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word64

PersistField ByteString

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: ByteString -> PersistValue

fromPersistValue :: PersistValue -> Either Text ByteString

PersistField Text

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Text -> PersistValue

fromPersistValue :: PersistValue -> Either Text Text

PersistField UTCTime

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: UTCTime -> PersistValue

fromPersistValue :: PersistValue -> Either Text UTCTime

PersistField Text

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Text -> PersistValue

fromPersistValue :: PersistValue -> Either Text0 Text

PersistField Html

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Html -> PersistValue

fromPersistValue :: PersistValue -> Either Text Html

PersistField TimeOfDay

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: TimeOfDay -> PersistValue

fromPersistValue :: PersistValue -> Either Text TimeOfDay

PersistField Day

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Day -> PersistValue

fromPersistValue :: PersistValue -> Either Text Day

PersistField PersistValue

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: PersistValue -> PersistValue

fromPersistValue :: PersistValue -> Either Text PersistValue

PersistField Checkmark

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Checkmark -> PersistValue

fromPersistValue :: PersistValue -> Either Text Checkmark

PersistField SomePersistField

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: SomePersistField -> PersistValue

fromPersistValue :: PersistValue -> Either Text SomePersistField

PersistField OverflowNatural

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: OverflowNatural -> PersistValue

fromPersistValue :: PersistValue -> Either Text OverflowNatural

PersistField [Char]

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: [Char] -> PersistValue

fromPersistValue :: PersistValue -> Either Text [Char]

PersistField a => PersistField [a]

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: [a] -> PersistValue

fromPersistValue :: PersistValue -> Either Text [a]

PersistField a => PersistField (Maybe a)

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Maybe a -> PersistValue

fromPersistValue :: PersistValue -> Either Text (Maybe a)

PersistField v => PersistField (IntMap v)

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: IntMap v -> PersistValue

fromPersistValue :: PersistValue -> Either Text (IntMap v)

(Ord a, PersistField a) => PersistField (Set a)

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Set a -> PersistValue

fromPersistValue :: PersistValue -> Either Text (Set a)

PersistField a => PersistField (Vector a)

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Vector a -> PersistValue

fromPersistValue :: PersistValue -> Either Text (Vector a)

(PersistEntity record, PersistField record, PersistField (Key record)) => PersistField (Entity record)

Defined in Database.Persist.Class.PersistEntity

Methods

toPersistValue :: Entity record -> PersistValue

fromPersistValue :: PersistValue -> Either Text (Entity record)

PersistField (BackendKey SqlBackend)

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

toPersistValue :: BackendKey SqlBackend -> PersistValue

fromPersistValue :: PersistValue -> Either Text (BackendKey SqlBackend)

PersistField (BackendKey SqlWriteBackend)

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

toPersistValue :: BackendKey SqlWriteBackend -> PersistValue

fromPersistValue :: PersistValue -> Either Text (BackendKey SqlWriteBackend)

PersistField (BackendKey SqlReadBackend)

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

toPersistValue :: BackendKey SqlReadBackend -> PersistValue

fromPersistValue :: PersistValue -> Either Text (BackendKey SqlReadBackend)

(BackendCompatible b s, PersistField (BackendKey b)) => PersistField (BackendKey (Compatible b s))

Defined in Database.Persist.Compatible.Types

Methods

toPersistValue :: BackendKey (Compatible b s) -> PersistValue

fromPersistValue :: PersistValue -> Either Text (BackendKey (Compatible b s))

(PersistField a, PersistField b) => PersistField (a, b)

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: (a, b) -> PersistValue

fromPersistValue :: PersistValue -> Either Text (a, b)

PersistField v => PersistField (Map Text v)

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Map Text v -> PersistValue

fromPersistValue :: PersistValue -> Either Text (Map Text v)

HasResolution a => PersistField (Fixed a)

Defined in Database.Persist.Class.PersistField

Methods

toPersistValue :: Fixed a -> PersistValue

fromPersistValue :: PersistValue -> Either Text (Fixed a)

PersistConfig

class PersistConfig c where

Represents a value containing all the configuration options for a specific backend. This abstraction makes it easier to write code that can easily swap backends.

Minimal complete definition

loadConfig, createPoolConfig, runPool

Associated Types

type PersistConfigBackend c :: (* -> *) -> * -> *

type PersistConfigPool c

Methods

loadConfig :: Value -> Parser c

Load the config settings from a Value, most likely taken from a YAML config file.

applyEnv :: c -> IO c

Modify the config settings based on environment variables.

createPoolConfig :: c -> IO (PersistConfigPool c)

Create a new connection pool based on the given config settings.

runPool :: MonadUnliftIO m => c -> PersistConfigBackend c m a -> PersistConfigPool c -> m a

Run a database action by taking a connection from the pool.

Instances

(PersistConfig c1, PersistConfig c2, PersistConfigPool c1 ~ PersistConfigPool c2, PersistConfigBackend c1 ~ PersistConfigBackend c2) => PersistConfig (Either c1 c2)

Defined in Database.Persist.Class.PersistConfig

Associated Types

type PersistConfigBackend (Either c1 c2) :: (Type -> Type) -> Type -> Type

type PersistConfigPool (Either c1 c2)

Methods

loadConfig :: Value -> Parser (Either c1 c2)

applyEnv :: Either c1 c2 -> IO (Either c1 c2)

createPoolConfig :: Either c1 c2 -> IO (PersistConfigPool (Either c1 c2))

runPool :: MonadUnliftIO m => Either c1 c2 -> PersistConfigBackend (Either c1 c2) m a -> PersistConfigPool (Either c1 c2) -> m a

entityValues :: PersistEntity record => Entity record -> [PersistValue]

Get list of values corresponding to given entity.

Lifting

class HasPersistBackend backend where

Class which allows the plucking of a BaseBackend backend from some larger type. For example, instance HasPersistBackend (SqlReadBackend, Int) where type BaseBackend (SqlReadBackend, Int) = SqlBackend persistBackend = unSqlReadBackend . fst

Associated Types

type BaseBackend backend

Methods

persistBackend :: backend -> BaseBackend backend

Instances

HasPersistBackend SqlBackend

Defined in Database.Persist.SqlBackend.Internal

Associated Types

type BaseBackend SqlBackend

Methods

persistBackend :: SqlBackend -> BaseBackend SqlBackend

HasPersistBackend SqlWriteBackend

Defined in Database.Persist.Sql.Types.Internal

Associated Types

type BaseBackend SqlWriteBackend

Methods

persistBackend :: SqlWriteBackend -> BaseBackend SqlWriteBackend

HasPersistBackend SqlReadBackend

Defined in Database.Persist.Sql.Types.Internal

Associated Types

type BaseBackend SqlReadBackend

Methods

persistBackend :: SqlReadBackend -> BaseBackend SqlReadBackend

(BackendCompatible b s, HasPersistBackend b) => HasPersistBackend (Compatible b s)

Defined in Database.Persist.Compatible.Types

Associated Types

type BaseBackend (Compatible b s)

Methods

persistBackend :: Compatible b s -> BaseBackend (Compatible b s)

withBaseBackend :: HasPersistBackend backend => ReaderT (BaseBackend backend) m a -> ReaderT backend m a

Run a query against a larger backend by plucking out BaseBackend backend

This is a helper for reusing existing queries when expanding the backend type.

Since: 2.12.0

class HasPersistBackend backend => IsPersistBackend backend

Class which witnesses that backend is essentially the same as BaseBackend backend. That is, they're isomorphic and backend is just some wrapper over BaseBackend backend.

Minimal complete definition

mkPersistBackend

Instances

IsPersistBackend SqlBackend

Defined in Database.Persist.SqlBackend.Internal

Methods

mkPersistBackend :: BaseBackend SqlBackend -> SqlBackend

IsPersistBackend SqlWriteBackend

Defined in Database.Persist.Sql.Types.Internal

Methods

mkPersistBackend :: BaseBackend SqlWriteBackend -> SqlWriteBackend

IsPersistBackend SqlReadBackend

Defined in Database.Persist.Sql.Types.Internal

Methods

mkPersistBackend :: BaseBackend SqlReadBackend -> SqlReadBackend

liftPersist :: (MonadIO m, MonadReader backend m) => ReaderT backend IO b -> m b

class BackendCompatible sup sub where

This class witnesses that two backend are compatible, and that you can convert from the sub backend into the sup backend. This is similar to the HasPersistBackend and IsPersistBackend classes, but where you don't want to fix the type associated with the PersistEntityBackend of a record.

Generally speaking, where you might have:

foo ::
  ( PersistEntity record
  , PeristEntityBackend record ~ BaseBackend backend
  , IsSqlBackend backend
  )

this can be replaced with:

foo ::
  ( PersistEntity record,
  , PersistEntityBackend record ~ backend
  , BackendCompatible SqlBackend backend
  )

This works for SqlReadBackend because of the instance BackendCompatible SqlBackend SqlReadBackend, without needing to go through the BaseBackend type family.

Likewise, functions that are currently hardcoded to use SqlBackend can be generalized:

-- before:
asdf :: ReaderT SqlBackend m ()
asdf = pure ()

-- after:
asdf' :: BackendCompatible SqlBackend backend => ReaderT backend m ()
asdf' = withCompatibleBackend asdf

Since: 2.7.1

Methods

projectBackend :: sub -> sup

Instances

BackendCompatible SqlBackend SqlBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

projectBackend :: SqlBackend -> SqlBackend

BackendCompatible SqlBackend SqlWriteBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

projectBackend :: SqlWriteBackend -> SqlBackend

BackendCompatible SqlBackend SqlReadBackend

Defined in Database.Persist.Sql.Orphan.PersistStore

Methods

projectBackend :: SqlReadBackend -> SqlBackend

withCompatibleBackend :: BackendCompatible sup sub => ReaderT sup m a -> ReaderT sub m a

Run a query against a compatible backend, by projecting the backend

This is a helper for using queries which run against a specific backend type that your backend is compatible with.

Since: 2.12.0

JSON utilities

keyValueEntityToJSON :: (PersistEntity record, ToJSON record) => Entity record -> Value

Predefined toJSON. The resulting JSON looks like {"key": 1, "value": {"name": ...}}.

The typical usage is:

instance ToJSON (Entity User) where
    toJSON = keyValueEntityToJSON

keyValueEntityFromJSON :: (PersistEntity record, FromJSON record) => Value -> Parser (Entity record)

Predefined parseJSON. The input JSON looks like {"key": 1, "value": {"name": ...}}.

The typical usage is:

instance FromJSON (Entity User) where
    parseJSON = keyValueEntityFromJSON

entityIdToJSON :: (PersistEntity record, ToJSON record) => Entity record -> Value

Predefined toJSON. The resulting JSON looks like {"id": 1, "name": ...}.

The typical usage is:

instance ToJSON (Entity User) where
    toJSON = entityIdToJSON

entityIdFromJSON :: (PersistEntity record, FromJSON record) => Value -> Parser (Entity record)

Predefined parseJSON. The input JSON looks like {"id": 1, "name": ...}.

The typical usage is:

instance FromJSON (Entity User) where
    parseJSON = entityIdFromJSON

toPersistValueJSON :: ToJSON a => a -> PersistValue

Convenience function for getting a free PersistField instance from a type with JSON instances.

Example usage in combination with fromPersistValueJSON:

instance PersistField MyData where
  fromPersistValue = fromPersistValueJSON
  toPersistValue = toPersistValueJSON

fromPersistValueJSON :: FromJSON a => PersistValue -> Either Text a

Convenience function for getting a free PersistField instance from a type with JSON instances. The JSON parser used will accept JSON values other that object and arrays. So, if your instance serializes the data to a JSON string, this will still work.

Example usage in combination with toPersistValueJSON:

instance PersistField MyData where
  fromPersistValue = fromPersistValueJSON
  toPersistValue = toPersistValueJSON