Database.Persist.TH

This module provides utilities for creating backends. Regular users do not need to use this module.

Parse entity defs

persistWith :: PersistSettings -> QuasiQuoter

Converts a quasi-quoted syntax into a list of entity definitions, to be used as input to the template haskell generation code (mkPersist).

persistUpperCase :: QuasiQuoter

Apply persistWith to upperCaseSettings.

persistLowerCase :: QuasiQuoter

Apply persistWith to lowerCaseSettings.

persistFileWith :: PersistSettings -> FilePath -> Q Exp

Same as persistWith, but uses an external file instead of a quasiquotation.

Deprecated synonyms

persist :: QuasiQuoter

Deprecated: Please use persistUpperCase instead.

Deprecate synonym for persistUpperCase.

persistFile :: FilePath -> Q Exp

Deprecated function. Equivalent to persistFileWith upperCaseSettings.

Turn EntityDefs into types

mkPersist :: MkPersistSettings -> [EntityDef] -> Q [Dec]

Create data types and appropriate PersistEntity instances for the given EntityDefs. Works well with the persist quasi-quoter.

data MkPersistSettings

Settings to be passed to the mkPersist function.

Constructors

MkPersistSettings

Fields

mpsBackend :: Type

Which database backend we're using.

When generating data types, each type is given a generic version- which works with any backend- and a type synonym for the commonly used backend. This is where you specify that commonly used backend.

sqlSettings :: MkPersistSettings

Use the SqlPersist backend.

Various other TH functions

mkMigrate :: String -> [EntityDef] -> Q [Dec]

Creates a single function to perform all migrations for the entities defined here. One thing to be aware of is dependencies: if you have entities with foreign references, make sure to place those definitions after the entities they reference.

mkSave :: String -> [EntityDef] -> Q [Dec]

Save the EntityDefs passed in under the given name.

mkDeleteCascade :: [EntityDef] -> Q [Dec]

Generate a DeleteCascade instance for the given EntityDefs.

share :: [[EntityDef] -> Q [Dec]] -> [EntityDef] -> Q [Dec]

Apply the given list of functions to the same EntityDefs.

This function is useful for cases such as:

>>> share [mkSave "myDefs", mkPersist sqlSettings] [persistLowerCase|...|]

derivePersistField :: String -> Q [Dec]

Automatically creates a valid PersistField instance for any datatype that has valid Show and Read instances. Can be very convenient for Enum types.

persistFieldFromEntity :: EntityDef -> Q [Dec]

produce code similar to the following:

instance PersistEntity e => PersistField e where toPersistValue = PersistMap $ zip columNames (map toPersistValue . toPersistFields) fromPersistValue (PersistMap o) = fromPersistValues $ map ((_,v) -> casefromPersistValue v of Left e -> error e Right r -> r) o fromPersistValue x = Left $ Expected PersistMap, received: ++ show x sqlType _ = SqlString

Deprecated

share2 :: ([EntityDef] -> Q [Dec]) -> ([EntityDef] -> Q [Dec]) -> [EntityDef] -> Q [Dec]

Deprecated: Use share instead

Deprecated, restricted version of share.