Yesod.Session.Persist.Storage

Documentation

persistentStorage :: forall record backend result m. (PersistRecordBackend record backend, PersistStoreWrite backend) => SessionPersistence backend record m -> StorageOperation result -> ReaderT backend IO result

data SessionPersistence backend record m

Mapping between Session and a Persistent entity of your choice

Constructors

(PersistRecordBackend record backend, PersistStoreWrite backend, SafeToInsert record) => SessionPersistence

Fields

• databaseKey :: SessionKey -> Key record
• toDatabase :: Session -> record
• fromDatabase :: record -> Session
• runDB :: forall a. ReaderT backend IO a -> m a

Persistent reëxports

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

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, tabulateEntityA, persistUniqueKeys, persistUniqueToFieldNames, persistUniqueToValues, fieldLens

type family PersistEntityBackend record

Persistent allows multiple different backends (databases).

class SafeToInsert a

A type class which is used to witness that a type is safe to insert into the database without providing a primary key.

The TemplateHaskell function mkPersist will generate instances of this class for any entity that it works on. If the entity has a default primary key, then it provides a regular instance. If the entity has a Primary natural key, then this works fine. But if the entity has an Id column with no default=, then this does a TypeError and forces the user to use insertKey.

Since: persistent-2.14.0.0

Instances

(TypeError (EntityErrorMessage a) :: Constraint) => SafeToInsert (Entity a)

Defined in Database.Persist.Class.PersistEntity

(TypeError (FunctionErrorMessage a b) :: Constraint) => SafeToInsert (a -> b)

Defined in Database.Persist.Class.PersistEntity

type ConnectionPool = Pool SqlBackend