Database.Persist.Class.PersistQuery

Documentation

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

Returns a [Entity record] corresponding to the filters and options provided.

Filters are constructed using the operators defined in Database.Persist (and re-exported from Database.Persist.Sql). Let's look at some examples:

usersWithAgeOver40 :: SqlPersistT IO [Entity User]
usersWithAgeOver40 =
    selectList [UserAge >=. 40] []

If you provide multiple values in the list, the conditions are ANDed together.

usersWithAgeBetween30And50 :: SqlPersistT IO [Entity User]
usersWithAgeBetween30And50 =
     selectList
         [ UserAge >=. 30
         , UserAge <=. 50
         ]
         []

The second list contains the SelectOpt for a record. We can select the first ten records with LimitTo

firstTenUsers =
    selectList [] [LimitTo 10]

And we can select the second ten users with OffsetBy.

secondTenUsers =
    selectList [] [LimitTo 10, OffsetBy 10]

Warning that LIMIT/OFFSET is bad for pagination!

With Asc and Desc, we can provide the field we want to sort on. We can provide multiple sort orders - later ones are used to sort records that are equal on the first field.

newestUsers =
    selectList [] [Desc UserCreatedAt, LimitTo 10]

oldestUsers =
    selectList [] [Asc UserCreatedAt, LimitTo 10]

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.

NOTE: This function returns an Acquire and a ConduitM, which implies that it streams from the database. It does not. Please use selectList to simplify the code. If you want streaming behavior, consider persistent-pagination which efficiently chunks a query into ranges, or investigate a backend-specific streaming solution.

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.

WARNING: This function returns a ConduitM, which implies that it streams the results. It does not stream results on most backends. If you need streaming, see persistent-pagination for a means of chunking results based on indexed ranges.

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.

For an example, see selectList.

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.