Database.Persist.Class

Documentation

class (PersistEntity record, PersistEntityBackend record ~ backend, PersistStore 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

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

Minimal complete definition

get, insert, insertKey, repsert, replace, delete, update

Associated Types

data BackendKey backend

Methods

get :: (MonadIO m, backend ~ PersistEntityBackend val, PersistEntity val) => Key val -> ReaderT backend m (Maybe val)

Get a record by identifier, if available.

insert :: (MonadIO m, backend ~ PersistEntityBackend val, PersistEntity val) => val -> ReaderT backend m (Key val)

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

insert_ :: (MonadIO m, backend ~ PersistEntityBackend val, PersistEntity val) => val -> ReaderT backend m ()

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

insertMany :: (MonadIO m, backend ~ PersistEntityBackend val, PersistEntity val) => [val] -> ReaderT backend m [Key val]

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, backend ~ PersistEntityBackend val, PersistEntity val) => [val] -> 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, backend ~ PersistEntityBackend val, PersistEntity val) => [Entity val] -> 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 backend inserts all the entities in one database query.

The SQL backends use the slow, default implementation of mapM_ insertKey.

insertKey :: (MonadIO m, backend ~ PersistEntityBackend val, PersistEntity val) => Key val -> val -> ReaderT backend m ()

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

repsert :: (MonadIO m, backend ~ PersistEntityBackend val, PersistEntity val) => Key val -> val -> 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.

replace :: (MonadIO m, backend ~ PersistEntityBackend val, PersistEntity val) => Key val -> val -> 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, backend ~ PersistEntityBackend val, PersistEntity val) => Key val -> ReaderT backend m ()

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

update :: (MonadIO m, PersistEntity val, backend ~ PersistEntityBackend val) => Key val -> [Update val] -> ReaderT backend m ()

Update individual fields on a specific record.

updateGet :: (MonadIO m, PersistEntity val, backend ~ PersistEntityBackend val) => Key val -> [Update val] -> ReaderT backend m val

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.

getJust :: (PersistStore backend, PersistEntity val, Show (Key val), backend ~ PersistEntityBackend val, MonadIO m) => Key val -> ReaderT backend m val

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

belongsTo :: (PersistStore backend, PersistEntity ent1, PersistEntity ent2, backend ~ PersistEntityBackend ent2, 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 foerignId

belongsToJust :: (PersistStore backend, PersistEntity ent1, PersistEntity ent2, backend ~ PersistEntityBackend ent2, MonadIO m) => (ent1 -> Key ent2) -> ent1 -> ReaderT backend m ent2

same as belongsTo, but uses getJust and therefore is similarly unsafe

insertEntity :: (PersistStore backend, PersistEntity e, backend ~ PersistEntityBackend e, MonadIO m) => e -> ReaderT backend m (Entity e)

like insert, but returns the complete Entity

PersistUnique

class PersistStore backend => PersistUnique 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.

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

getBy, deleteBy

Methods

getBy :: (MonadIO m, backend ~ PersistEntityBackend val, PersistEntity val) => Unique val -> ReaderT backend m (Maybe (Entity val))

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

deleteBy :: (MonadIO m, PersistEntityBackend val ~ backend, PersistEntity val) => Unique val -> ReaderT backend m ()

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

insertUnique :: (MonadIO m, PersistEntityBackend val ~ backend, PersistEntity val) => val -> ReaderT backend m (Maybe (Key val))

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

upsert

Arguments

:: (MonadIO m, PersistEntityBackend val ~ backend, PersistEntity val)

=> val

new record to insert

-> [Update val]

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 val)

the record in the database after the operation

update based on a uniquness constraint or insert

insert the new record if it does not exist update the existing record that matches the uniqueness contraint

Throws an exception if there is more than 1 uniqueness contraint

getByValue :: (MonadIO m, PersistEntity record, PersistUnique backend, PersistEntityBackend 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, PersistEntity val, PersistUnique backend, PersistEntityBackend val ~ backend) => val -> ReaderT backend m (Either (Entity val) (Key val))

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.

replaceUnique :: (MonadIO m, Eq record, Eq (Unique record), PersistEntityBackend record ~ backend, PersistEntity record, PersistUnique 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, PersistEntityBackend record ~ backend, PersistEntity record, PersistUnique 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, PersistEntity val, PersistUnique backend, PersistEntityBackend val ~ backend) => val -> ReaderT backend m (Unique val)

Return the single unique key for a record

PersistQuery

class PersistStore backend => PersistQuery backend where

Minimal complete definition

updateWhere, deleteWhere, selectSourceRes, selectKeysRes, count

Methods

updateWhere :: (MonadIO m, PersistEntity val, backend ~ PersistEntityBackend val) => [Filter val] -> [Update val] -> ReaderT backend m ()

Update individual fields on any record matching the given criterion.

deleteWhere :: (MonadIO m, PersistEntity val, backend ~ PersistEntityBackend val) => [Filter val] -> ReaderT backend m ()

Delete all records matching the given criterion.

selectSourceRes :: (PersistEntity val, PersistEntityBackend val ~ backend, MonadIO m1, MonadIO m2) => [Filter val] -> [SelectOpt val] -> ReaderT backend m1 (Acquire (Source m2 (Entity val)))

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

selectFirst :: (MonadIO m, PersistEntity val, backend ~ PersistEntityBackend val) => [Filter val] -> [SelectOpt val] -> ReaderT backend m (Maybe (Entity val))

get just the first record for the criterion

selectKeysRes :: (MonadIO m1, MonadIO m2, PersistEntity val, backend ~ PersistEntityBackend val) => [Filter val] -> [SelectOpt val] -> ReaderT backend m1 (Acquire (Source m2 (Key val)))

Get the Keys of all records matching the given criterion.

count :: (MonadIO m, PersistEntity val, backend ~ PersistEntityBackend val) => [Filter val] -> ReaderT backend m Int

The total number of records fulfilling the given criterion.

selectSource :: (PersistQuery backend, MonadResource m, PersistEntity val, PersistEntityBackend val ~ backend, MonadReader env m, HasPersistBackend env backend) => [Filter val] -> [SelectOpt val] -> Source m (Entity val)

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

selectKeys :: (PersistQuery backend, MonadResource m, PersistEntity val, backend ~ PersistEntityBackend val, MonadReader env m, HasPersistBackend env backend) => [Filter val] -> [SelectOpt val] -> Source m (Key val)

Get the Keys of all records matching the given criterion.

selectList :: (MonadIO m, PersistEntity val, PersistQuery backend, PersistEntityBackend val ~ backend) => [Filter val] -> [SelectOpt val] -> ReaderT backend m [Entity val]

Call selectSource but return the result as a list.

selectKeysList :: (MonadIO m, PersistEntity val, PersistQuery backend, PersistEntityBackend val ~ backend) => [Filter val] -> [SelectOpt val] -> ReaderT backend m [Key val]

Call selectKeys but return the result as a list.

DeleteCascade

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

Methods

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

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

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.

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

A value which can be marshalled to and from a PersistValue.

Methods

toPersistValue :: a -> PersistValue

fromPersistValue :: PersistValue -> Either Text a

Instances

PersistField Bool

PersistField Double

PersistField Int

PersistField Int8

PersistField Int16

PersistField Int32

PersistField Int64

PersistField Rational

PersistField Word

PersistField Word8

PersistField Word16

PersistField Word32

PersistField Word64

PersistField String

PersistField ByteString

PersistField Text

PersistField UTCTime

PersistField Text

PersistField Natural

PersistField Html

PersistField TimeOfDay

PersistField Day

PersistField PersistValue

PersistField Checkmark

PersistField SomePersistField

PersistField a => PersistField [a]

PersistField a => PersistField (Maybe a)

HasResolution a => PersistField (Fixed a)

PersistField v => PersistField (IntMap v)

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

PersistField a => PersistField (Vector a)

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

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

PersistField v => PersistField (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 :: (MonadBaseControl IO m, MonadIO 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)

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

Lifting

class HasPersistBackend env backend | env -> backend where

Methods

persistBackend :: env -> backend

Instances

HasPersistBackend SqlBackend SqlBackend

liftPersist :: (MonadReader env m, HasPersistBackend env backend, MonadIO m) => ReaderT backend IO a -> m a

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 withfromPersistValueJSON:

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 withtoPersistValueJSON:

instance PersistField MyData where
  fromPersistValue = fromPersistValueJSON
  toPersistValue = toPersistValueJSON