Database.Groundhog

This module exports the most commonly used functions and datatypes.

See http://github.com/lykahb/groundhog/blob/master/examples/.

Core datatypes and functions

class (Monad m, DbDescriptor (PhantomDb m)) => PersistBackend m where

Associated Types

type PhantomDb m

A token which defines the DB type. For example, different monads working with Sqlite, return may Sqlite type.

Methods

insert :: PersistEntity v => v -> m (AutoKey v)

Insert a new record to a database and return its autogenerated key or ()

insert_ :: PersistEntity v => v -> m ()

Insert a new record to a database. For some backends it may be faster than insert.

insertBy :: (PersistEntity v, IsUniqueKey (Key v (Unique u))) => u (UniqueMarker v) -> v -> m (Either (AutoKey v) (AutoKey v))

Try to insert a record and return Right newkey. If there is a constraint violation for the given constraint, Left oldkey is returned , where oldkey is an identifier of the record with the matching values.

insertByAll :: PersistEntity v => v -> m (Either (AutoKey v) (AutoKey v))

Try to insert a record and return Right newkey. If there is a constraint violation for any constraint, Left oldkey is returned , where oldkey is an identifier of the record with the matching values. Note that if several constraints are violated, a key of an arbitrary matching record is returned.

replace :: (PersistEntity v, PrimitivePersistField (Key v BackendSpecific)) => Key v BackendSpecific -> v -> m ()

Replace a record with the given autogenerated key. Result is undefined if the record does not exist.

replaceBy :: (PersistEntity v, IsUniqueKey (Key v (Unique u))) => u (UniqueMarker v) -> v -> m ()

Replace a record. The unique key marker defines what unique key of the entity is used.

select :: (PersistEntity v, EntityConstr v c, HasSelectOptions opts (PhantomDb m) (RestrictionHolder v c)) => opts -> m [v]

Return a list of the records satisfying the condition. Example: select $ (FirstField ==. "abc" &&. SecondField >. "def") `orderBy` [Asc ThirdField] `limitTo` 100

selectAll :: PersistEntity v => m [(AutoKey v, v)]

Return a list of all records. Order is undefined. It can be useful for datatypes with multiple constructors.

get :: (PersistEntity v, PrimitivePersistField (Key v BackendSpecific)) => Key v BackendSpecific -> m (Maybe v)

Fetch an entity from a database

getBy :: (PersistEntity v, IsUniqueKey (Key v (Unique u))) => Key v (Unique u) -> m (Maybe v)

Fetch an entity from a database by its unique key

update :: (PersistEntity v, EntityConstr v c) => [Update (PhantomDb m) (RestrictionHolder v c)] -> Cond (PhantomDb m) (RestrictionHolder v c) -> m ()

Update the records satisfying the condition. Example: update [FirstField =. "abc"] $ FirstField ==. "def"

delete :: (PersistEntity v, EntityConstr v c) => Cond (PhantomDb m) (RestrictionHolder v c) -> m ()

Remove the records satisfying the condition

deleteBy :: (PersistEntity v, PrimitivePersistField (Key v BackendSpecific)) => Key v BackendSpecific -> m ()

Remove the record with given key. No-op if the record does not exist

deleteAll :: PersistEntity v => v -> m ()

Remove all records. The entity parameter is used only for type inference.

count :: (PersistEntity v, EntityConstr v c) => Cond (PhantomDb m) (RestrictionHolder v c) -> m Int

Count total number of records satisfying the condition

countAll :: PersistEntity v => v -> m Int

Count total number of records with all constructors. The entity parameter is used only for type inference

project :: (PersistEntity v, EntityConstr v c, Projection' p (PhantomDb m) (RestrictionHolder v c) a, HasSelectOptions opts (PhantomDb m) (RestrictionHolder v c)) => p -> opts -> m [a]

Fetch projection of some fields. Example: project (SecondField, ThirdField) $ (FirstField ==. "abc" &&. SecondField >. "def") `orderBy` [Asc ThirdField] `offsetBy` 100

migrate :: PersistEntity v => v -> Migration m

Check database schema and create migrations for the entity and the entities it contains

executeRaw

Arguments

:: Bool

keep in cache

-> String

query

-> [PersistValue]

positional parameters

-> m ()

Execute raw query

queryRaw

Arguments

:: Bool

keep in cache

-> String

query

-> [PersistValue]

positional parameters

-> (RowPopper m -> m a)

results processing function

-> m a

Execute raw query with results

insertList :: PersistField a => [a] -> m Int64

getList :: PersistField a => Int64 -> m [a]

newtype DbPersist conn m a

Constructors

DbPersist

Fields

unDbPersist :: ReaderT conn m a

Instances

MonadBaseControl IO m => MonadBaseControl IO (DbPersist conn m)

MonadBase IO m => MonadBase IO (DbPersist conn m)

MonadError e m => MonadError e (DbPersist conn m)

Monad m => MonadReader conn (DbPersist conn m)

MonadState s m => MonadState s (DbPersist conn m)

MonadWriter w m => MonadWriter w (DbPersist conn m)

MonadTrans (DbPersist conn)

MonadTransControl (DbPersist conn)

Monad m => Monad (DbPersist conn m)

Functor m => Functor (DbPersist conn m)

Applicative m => Applicative (DbPersist conn m)

MonadLogger m => MonadLogger (DbPersist conn m)

MonadIO m => MonadIO (DbPersist conn m)

MonadCont m => MonadCont (DbPersist conn m)

type StT (DbPersist conn) a = StT (ReaderT conn) a

type StM (DbPersist conn m) a = ComposeSt (DbPersist conn) m a

data Unique u

A holder for Unique constraints

data UniqueMarker v a

A phantom datatype to make instance head different u (UniqueMarker v)

Instances

(PersistEntity v, DbDescriptor db, IsUniqueKey k, (~) * k (Key v (Unique u)), (~) * (RestrictionHolder v c) r') => Expression db r' (u (UniqueMarker v))

(PersistEntity v, IsUniqueKey k, (~) * k (Key v (Unique u))) => FieldLike (u (UniqueMarker v)) k

(PersistEntity v, IsUniqueKey k, (~) * k (Key v (Unique u))) => Assignable (u (UniqueMarker v)) k

(PersistEntity v, IsUniqueKey k, (~) * k (Key v (Unique u))) => Projection (u (UniqueMarker v)) k

type ProjectionDb (u (UniqueMarker v)) db = ()

type ProjectionRestriction (u (UniqueMarker v)) (RestrictionHolder v' c) = (~) * v v'

data BackendSpecific

Key marked with this type can have value for any backend

extractUnique :: (IsUniqueKey uKey, uKey ~ Key v u) => v -> uKey

Creates value of unique key using the data extracted from the passed value

data Cond db r

Represents condition for a query.

Constructors

And (Cond db r) (Cond db r)

Or (Cond db r) (Cond db r)

Not (Cond db r)

Compare ExprRelation (UntypedExpr db r) (UntypedExpr db r)

CondRaw (QueryRaw db r)

CondEmpty

Instances

((~) * db' db, (~) * r' r) => Expression db' r' (Cond db r)

(~) * a Bool => Projection (Cond db r) a

(~) * db' db => HasSelectOptions (Cond db r) db' r

type HasLimit (Cond db r) = HFalse

type HasOffset (Cond db r) = HFalse

type HasOrder (Cond db r) = HFalse

type HasDistinct (Cond db r) = HFalse

type ProjectionDb (Cond db r) db' = (~) * db db'

type ProjectionRestriction (Cond db r) r' = (~) * r r'

data Order db r

Defines sort order of a result-set

Constructors

forall a f . Projection' f db r a => Asc f

forall a f . Projection' f db r a => Desc f

data AutoKeyField v c where

It can be used in expressions like a regular field. For example, delete (AutoKeyField ==. k) or delete (AutoKeyField ==. k ||. SomeField ==. "DUPLICATE")

Constructors

AutoKeyField :: AutoKeyField v c

Instances

(EntityConstr v c, DbDescriptor db, (~) * (RestrictionHolder v c) r') => Expression db r' (AutoKeyField v c)

(EntityConstr v c, (~) * a (AutoKey v)) => FieldLike (AutoKeyField v c) a

(EntityConstr v c, (~) * a (AutoKey v)) => Assignable (AutoKeyField v c) a

(EntityConstr v c, (~) * a (AutoKey v)) => Projection (AutoKeyField v c) a

type ProjectionDb (AutoKeyField v c) db = ()

type ProjectionRestriction (AutoKeyField v c) r = (~) * r (RestrictionHolder v c)

(~>) :: (EntityConstr v c, FieldLike f a, DbDescriptor db, Projection' f db (RestrictionHolder v c) a, Embedded a) => f -> Selector a a' -> SubField db v c a' infixl 5

Accesses fields of the embedded datatypes. For example, SomeField ==. ("abc", "def") ||. SomeField ~> Tuple2_0Selector ==. "def"

limitTo :: (HasSelectOptions a db r, HasLimit a ~ HFalse) => a -> Int -> SelectOptions db r HTrue (HasOffset a) (HasOrder a) (HasDistinct a)

offsetBy :: (HasSelectOptions a db r, HasOffset a ~ HFalse) => a -> Int -> SelectOptions db r (HasLimit a) HTrue (HasOrder a) (HasDistinct a)

orderBy :: (HasSelectOptions a db r, HasOrder a ~ HFalse) => a -> [Order db r] -> SelectOptions db r (HasLimit a) (HasOffset a) HTrue (HasDistinct a)

deleteByKey :: (PersistBackend m, PersistEntity v, PrimitivePersistField (Key v BackendSpecific)) => Key v BackendSpecific -> m ()

Deprecated: Use deleteBy instead

Expressions

(=.) :: (Assignable f a', ProjectionDb f db, ProjectionRestriction f r, Expression db r b, Unifiable f b) => f -> b -> Update db r infixr 3

Update field

(&&.) :: Cond db r -> Cond db r -> Cond db r infixr 3

Boolean "and" operator.

(||.) :: Cond db r -> Cond db r -> Cond db r infixr 2

Boolean "or" operator.

(==.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r infix 4

(/=.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r infix 4

(<.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r infix 4

(<=.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r infix 4

(>.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r infix 4

(>=.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r infix 4

isFieldNothing :: (Expression db r f, Projection f (Maybe a), PrimitivePersistField (Maybe a), Unifiable f (Maybe a)) => f -> Cond db r

This function more limited than (==.), but has better type inference. If you want to compare your value to Nothing with (==.) operator, you have to write the types explicitly myExpr ==. (Nothing :: Maybe Int). TODO: restrict db r

liftExpr :: ExpressionOf db r a a' => a -> Expr db r a'

Converts value to Expr. It can help to pass values of different types into functions which expect arguments of the same type, like (+).

toArith :: ExpressionOf db r a a' => a -> Expr db r a'

Deprecated: Please use liftExpr instead

It is kept for compatibility with older Groundhog versions and can be replaced with "liftExpr".

Migration

createMigration :: Monad m => Migration m -> m NamedMigrations

Produce the migrations but not execute them. Fails when an unsafe migration occurs.

executeMigration :: (PersistBackend m, MonadIO m) => NamedMigrations -> m ()

Execute the migrations with printing to stderr. Fails when an unsafe migration occurs.

executeMigrationUnsafe :: (PersistBackend m, MonadIO m) => NamedMigrations -> m ()

Execute migrations. Executes the unsafe migrations without warnings and prints them to stderr

runMigration :: (PersistBackend m, MonadIO m) => Migration m -> m ()

Creates migrations and executes them with printing to stderr. Fails when an unsafe migration occurs. > runMigration m = createMigration m >>= executeMigration

runMigrationUnsafe :: (PersistBackend m, MonadIO m) => Migration m -> m ()

Creates migrations and executes them with printing to stderr. Executes the unsafe migrations without warnings > runMigrationUnsafe m = createMigration m >>= executeMigrationUnsafe

printMigration :: MonadIO m => NamedMigrations -> m ()

Pretty print the migrations