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.

Minimal complete definition

toBackendKey, fromBackendKey

Methods

toBackendKey :: Key record -> BackendKey backend

fromBackendKey :: BackendKey backend -> Key record

PersistStore

class PersistCore backend

Associated Types

data BackendKey backend

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

Get a record by identifier, if available.

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

Get many records by their respective identifiers, if available.

Since: 2.8.1

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 :: (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).

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

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

insertMany :: (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.

insertMany_ :: (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.

insertEntityMany :: (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.

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

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

repsert :: (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.

repsertMany :: (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.

Differs from insertEntityMany by gracefully skipping pre-existing records matching key(s). @since 2.8.1

replace :: (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.

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

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

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

Update individual fields on a specific record.

updateGet :: (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.

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

A convenient alias for common type signatures

getJust :: (PersistStoreRead backend, Show (Key record), 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.

getJustEntity :: (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.

Since: 2.6.1

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

Like get, but returns the complete Entity.

belongsTo :: (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 :: (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 :: (PersistStoreWrite backend, PersistRecordBackend e backend, MonadIO m) => e -> ReaderT backend m (Entity e)

Like insert, but returns the complete Entity.

insertRecord :: (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.

Since: 2.6.1

PersistUnique

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 (PersistCore backend, 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.

Minimal complete definition

getBy

Methods

getBy :: (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.

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

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

insertUnique :: (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.

upsert

Arguments

:: (MonadIO m, PersistRecordBackend record backend)

=> record

new record to insert

-> [Update record]

updates to perform if the record already exists (leaving this empty is the equivalent of performing a repsert on a unique key)

-> 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.

Throws an exception if there is more than 1 uniqueness constraint.

upsertBy

Arguments

:: (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 (leaving this empty is the equivalent of performing a repsert on a unique key)

-> 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.

putMany

Arguments

:: (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

getByValue :: (MonadIO m, PersistUniqueRead backend, PersistRecordBackend record backend) => 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.

insertBy :: (MonadIO m, PersistUniqueWrite backend, PersistRecordBackend record backend) => 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.

insertUniqueEntity :: (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.

Since: 2.7.1

replaceUnique :: (MonadIO m, Eq record, 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 :: (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

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

Return the single unique key for a record.

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

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.

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

Backends supporting conditional write operations

Minimal complete definition

updateWhere, deleteWhere

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.

selectSource :: (PersistQueryRead (BaseBackend backend), MonadResource m, PersistEntity record, PersistEntityBackend record ~ BaseBackend (BaseBackend backend), MonadReader backend m, HasPersistBackend backend) => [Filter record] -> [SelectOpt record] -> ConduitM () (Entity record) m ()

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

selectKeys :: (PersistQueryRead (BaseBackend backend), MonadResource m, PersistEntity record, BaseBackend (BaseBackend backend) ~ PersistEntityBackend record, MonadReader backend m, HasPersistBackend backend) => [Filter record] -> [SelectOpt record] -> ConduitM () (Key record) m ()

Get the Keys of all records matching the given criterion.

selectList :: (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 :: (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.

Minimal complete definition

deleteCascade

Methods

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

Perform cascade-deletion of single database entry.

deleteCascadeWhere :: (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.

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 :: Monad m => m 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 -> [(HaskellName, DBName)]

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.

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.

Minimal complete definition

toPersistValue, fromPersistValue

Methods

toPersistValue :: a -> PersistValue

fromPersistValue :: PersistValue -> Either Text a

Instances

PersistField Bool

Methods

toPersistValue :: Bool -> PersistValue

fromPersistValue :: PersistValue -> Either Text Bool

PersistField Double

Methods

toPersistValue :: Double -> PersistValue

fromPersistValue :: PersistValue -> Either Text Double

PersistField Int

Methods

toPersistValue :: Int -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int

PersistField Int8

Methods

toPersistValue :: Int8 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int8

PersistField Int16

Methods

toPersistValue :: Int16 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int16

PersistField Int32

Methods

toPersistValue :: Int32 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int32

PersistField Int64

Methods

toPersistValue :: Int64 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Int64

PersistField Natural

Methods

toPersistValue :: Natural -> PersistValue

fromPersistValue :: PersistValue -> Either Text Natural

PersistField Rational

Methods

toPersistValue :: Rational -> PersistValue

fromPersistValue :: PersistValue -> Either Text Rational

PersistField Word

Methods

toPersistValue :: Word -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word

PersistField Word8

Methods

toPersistValue :: Word8 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word8

PersistField Word16

Methods

toPersistValue :: Word16 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word16

PersistField Word32

Methods

toPersistValue :: Word32 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word32

PersistField Word64

Methods

toPersistValue :: Word64 -> PersistValue

fromPersistValue :: PersistValue -> Either Text Word64

PersistField ByteString

Methods

toPersistValue :: ByteString -> PersistValue

fromPersistValue :: PersistValue -> Either Text ByteString

PersistField Text

Methods

toPersistValue :: Text -> PersistValue

fromPersistValue :: PersistValue -> Either Text Text

PersistField UTCTime

Methods

toPersistValue :: UTCTime -> PersistValue

fromPersistValue :: PersistValue -> Either Text UTCTime

PersistField Text

Methods

toPersistValue :: Text -> PersistValue

fromPersistValue :: PersistValue -> Either Text Text

PersistField Html

Methods

toPersistValue :: Html -> PersistValue

fromPersistValue :: PersistValue -> Either Text Html

PersistField TimeOfDay

Methods

toPersistValue :: TimeOfDay -> PersistValue

fromPersistValue :: PersistValue -> Either Text TimeOfDay

PersistField Day

Methods

toPersistValue :: Day -> PersistValue

fromPersistValue :: PersistValue -> Either Text Day

PersistField PersistValue

Methods

toPersistValue :: PersistValue -> PersistValue

fromPersistValue :: PersistValue -> Either Text PersistValue

PersistField Checkmark

Methods

toPersistValue :: Checkmark -> PersistValue

fromPersistValue :: PersistValue -> Either Text Checkmark

PersistField SomePersistField

Methods

toPersistValue :: SomePersistField -> PersistValue

fromPersistValue :: PersistValue -> Either Text SomePersistField

PersistField [Char]

Methods

toPersistValue :: [Char] -> PersistValue

fromPersistValue :: PersistValue -> Either Text [Char]

PersistField a => PersistField [a]

Methods

toPersistValue :: [a] -> PersistValue

fromPersistValue :: PersistValue -> Either Text [a]

PersistField a => PersistField (Maybe a)

Methods

toPersistValue :: Maybe a -> PersistValue

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

HasResolution a => PersistField (Fixed a)

Methods

toPersistValue :: Fixed a -> PersistValue

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

PersistField v => PersistField (IntMap v)

Methods

toPersistValue :: IntMap v -> PersistValue

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

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

Methods

toPersistValue :: Set a -> PersistValue

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

PersistField a => PersistField (Vector a)

Methods

toPersistValue :: Vector a -> PersistValue

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

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

Methods

toPersistValue :: Entity record -> PersistValue

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

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

Methods

toPersistValue :: (a, b) -> PersistValue

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

PersistField v => PersistField (Map Text v)

Methods

toPersistValue :: Map Text v -> PersistValue

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

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)

Associated Types

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

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

Minimal complete definition

persistBackend

Associated Types

type BaseBackend backend

Methods

persistBackend :: backend -> BaseBackend backend

Instances

HasPersistBackend SqlWriteBackend

Associated Types

type BaseBackend SqlWriteBackend :: *

Methods

persistBackend :: SqlWriteBackend -> BaseBackend SqlWriteBackend

HasPersistBackend SqlReadBackend

Associated Types

type BaseBackend SqlReadBackend :: *

Methods

persistBackend :: SqlReadBackend -> BaseBackend SqlReadBackend

HasPersistBackend SqlBackend

Associated Types

type BaseBackend SqlBackend :: *

Methods

persistBackend :: SqlBackend -> BaseBackend SqlBackend

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 SqlWriteBackend

Methods

mkPersistBackend :: BaseBackend SqlWriteBackend -> SqlWriteBackend

IsPersistBackend SqlReadBackend

Methods

mkPersistBackend :: BaseBackend SqlReadBackend -> SqlReadBackend

IsPersistBackend SqlBackend

Methods

mkPersistBackend :: BaseBackend SqlBackend -> SqlBackend

liftPersist :: (MonadIO m, MonadReader backend m, HasPersistBackend backend) => ReaderT (BaseBackend 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' = withReaderT projectBackend asdf

Since: 2.7.1

Minimal complete definition

projectBackend

Methods

projectBackend :: sub -> sup

JSON utilities

keyValueEntityToJSON :: (PersistEntity record, ToJSON record, ToJSON (Key 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, FromJSON (Key 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, ToJSON (Key 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, FromJSON (Key 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