Database.Persist.Sql.Lifted.Expression.Type

Documentation

data SqlExpr a

An expression on the SQL backend.

Raw expression: Contains a SqlExprMeta and a function for building the expr. It recieves a parameter telling it whether it is in a parenthesized context, and takes information about the SQL connection (mainly for escaping names) and returns both an string (Builder) and a list of values to be interpolated by the SQL backend.

Instances

(TypeError SqlExprFunctorMessage :: Constraint) => Functor SqlExpr

Folks often want the ability to promote a Haskell function into the SqlExpr expression language - and naturally reach for fmap. Unfortunately, this is impossible. We cannot send *functions* to the database, which is what we would need to do in order for this to make sense. Let's consider the type of fmap for SqlExpr:

fmap :: (a -> b) -> SqlExpr a -> SqlExpr b

This type signature is making a pretty strong claim: "Give me a Haskell function from a -> b. I will then transform a SQL expression representing a Haskell value of type a and turn it into a SQL expression representing a Haskell value of type b."

Let's suppose we *could* do this - fmap (+1) would have to somehow inspect the function expression means "add one", and then translate that to the appropriate SQL.

This is why esqueleto defines a bunch of operators: x +. (val 1) can be used instead of fmap (+1) x.

If you do have a SQL function, then you can provide a safe type and introduce it with unsafeSqlFunction or unsafeSqlBinOp.

Since: esqueleto-3.5.8.2

Defined in Database.Esqueleto.Internal.Internal

Methods

fmap :: (a -> b) -> SqlExpr a -> SqlExpr b

(<$) :: a -> SqlExpr b -> SqlExpr a

(PersistEntity rec, PersistField typ, SymbolToField sym rec typ) => HasField (sym :: Symbol) (SqlExpr (Entity rec)) (SqlExpr (Value typ))

This instance allows you to use record.field notation with GHC 9.2's OverloadedRecordDot extension.

Example:

-- persistent model:
BlogPost
    authorId     PersonId
    title        Text

-- query:
select $ do
    bp <- from $ table @BlogPost
    pure $ bp.title

This is exactly equivalent to the following:

blogPost :: SqlExpr (Entity BlogPost)

blogPost ^. BlogPostTitle
blogPost ^. #title
blogPost.title

There's another instance defined on SqlExpr (Entity (Maybe rec)), which allows you to project from a LEFT JOINed entity.

Since: esqueleto-3.5.4.0

Defined in Database.Esqueleto.Internal.Internal

Methods

getField :: SqlExpr (Entity rec) -> SqlExpr (Value typ)

(PersistEntity rec, PersistField typ, PersistField typ', SymbolToField sym rec typ, NullableFieldProjection typ typ', HasField sym (SqlExpr (Maybe (Entity rec))) (SqlExpr (Value (Maybe typ')))) => HasField (sym :: Symbol) (SqlExpr (Maybe (Entity rec))) (SqlExpr (Value (Maybe typ')))

This instance allows you to use record.field notation with GC 9.2's OverloadedRecordDot extension.

Example:

-- persistent model:
Person
    name         Text

BlogPost
    title        Text
    authorId     PersonId

-- query:

select $ do
    (p :& bp) <- from $
        table Person
        leftJoin table BlogPost
        on do
            \(p :& bp) ->
                just p.id ==. bp.authorId
    pure (p.name, bp.title)

The following forms are all equivalent:

blogPost :: SqlExpr (Maybe (Entity BlogPost))

blogPost ?. BlogPostTitle
blogPost ?. #title
blogPost.title

Since: esqueleto-3.5.4.0

Defined in Database.Esqueleto.Internal.Internal

Methods

getField :: SqlExpr (Maybe (Entity rec)) -> SqlExpr (Value (Maybe typ'))

(ToFrom a a', SqlSelect b r, ToAlias b, ToAliasReference b, d ~ (a' :& b)) => DoInnerJoin Lateral a (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) d

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doInnerJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) -> From d

(ToFrom a a', ToMaybe b, d ~ (a' :& ToMaybeT b), SqlSelect b r, ToAlias b, ToAliasReference b) => DoLeftJoin Lateral a (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) d

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doLeftJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) -> From d

ToAlias (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToAlias

Methods

toAlias :: SqlExpr (Value a) -> SqlQuery (SqlExpr (Value a))

ToAlias (SqlExpr (Entity a))

Defined in Database.Esqueleto.Experimental.ToAlias

Methods

toAlias :: SqlExpr (Entity a) -> SqlQuery (SqlExpr (Entity a))

ToAlias (SqlExpr (Maybe (Entity a)))

Defined in Database.Esqueleto.Experimental.ToAlias

Methods

toAlias :: SqlExpr (Maybe (Entity a)) -> SqlQuery (SqlExpr (Maybe (Entity a)))

ToAliasReference (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToAliasReference

Methods

toAliasReference :: Ident -> SqlExpr (Value a) -> SqlQuery (SqlExpr (Value a))

ToAliasReference (SqlExpr (Entity a))

Defined in Database.Esqueleto.Experimental.ToAliasReference

Methods

toAliasReference :: Ident -> SqlExpr (Entity a) -> SqlQuery (SqlExpr (Entity a))

ToAliasReference (SqlExpr (Maybe (Entity a)))

Defined in Database.Esqueleto.Experimental.ToAliasReference

Methods

toAliasReference :: Ident -> SqlExpr (Maybe (Entity a)) -> SqlQuery (SqlExpr (Maybe (Entity a)))

ToMaybe (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToMaybe

Associated Types

type ToMaybeT (SqlExpr (Value a))

Methods

toMaybe :: SqlExpr (Value a) -> ToMaybeT (SqlExpr (Value a))

ToMaybe (SqlExpr (Entity a))

Defined in Database.Esqueleto.Experimental.ToMaybe

Associated Types

type ToMaybeT (SqlExpr (Entity a))

Methods

toMaybe :: SqlExpr (Entity a) -> ToMaybeT (SqlExpr (Entity a))

ToMaybe (SqlExpr (Maybe a))

Defined in Database.Esqueleto.Experimental.ToMaybe

Associated Types

type ToMaybeT (SqlExpr (Maybe a))

Methods

toMaybe :: SqlExpr (Maybe a) -> ToMaybeT (SqlExpr (Maybe a))

FromPreprocess (SqlExpr (Entity val)) => From (SqlExpr (Entity val))

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (SqlExpr (Entity val))

FromPreprocess (SqlExpr (Maybe (Entity val))) => From (SqlExpr (Maybe (Entity val)))

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (SqlExpr (Maybe (Entity val)))

(PersistEntity val, BackendCompatible SqlBackend (PersistEntityBackend val)) => FromPreprocess (SqlExpr (Entity val))

Defined in Database.Esqueleto.Internal.Internal

Methods

fromPreprocess :: SqlQuery (PreprocessedFrom (SqlExpr (Entity val)))

(PersistEntity val, BackendCompatible SqlBackend (PersistEntityBackend val)) => FromPreprocess (SqlExpr (Maybe (Entity val)))

Defined in Database.Esqueleto.Internal.Internal

Methods

fromPreprocess :: SqlQuery (PreprocessedFrom (SqlExpr (Maybe (Entity val))))

PersistEntity val => LockableEntity (SqlExpr (Entity val))

Defined in Database.Esqueleto.Internal.Internal

Methods

flattenLockableEntity :: SqlExpr (Entity val) -> NonEmpty LockableSqlExpr

ToSomeValues (SqlExpr (Value a))

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: SqlExpr (Value a) -> [SomeValue]

a ~ Value b => UnsafeSqlFunctionArgument (SqlExpr a)

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: SqlExpr a -> [SqlExpr (Value ())]

PersistEntity ent => ToFrom (Table ent) (SqlExpr (Entity ent))

Defined in Database.Esqueleto.Experimental.From

Methods

toFrom :: Table ent -> From (SqlExpr (Entity ent))

PersistEntity e => SqlSelect (SqlExpr (Insertion e)) (Insertion e)

INSERT INTO hack.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Insertion e) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Insertion e)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Insertion e)

sqlInsertInto :: IdentInfo -> SqlExpr (Insertion e) -> (Builder, [PersistValue])

PersistField a => SqlSelect (SqlExpr (Value a)) (Value a)

You may return any single value (i.e. a single column) from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Value a)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Value a)

sqlInsertInto :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

PersistEntity a => SqlSelect (SqlExpr (Entity a)) (Entity a)

You may return an Entity from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Entity a) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Entity a)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Entity a)

sqlInsertInto :: IdentInfo -> SqlExpr (Entity a) -> (Builder, [PersistValue])

PersistEntity a => SqlSelect (SqlExpr (Maybe (Entity a))) (Maybe (Entity a))

You may return a possibly-NULL Entity from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Maybe (Entity a)) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Maybe (Entity a))) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Maybe (Entity a))

sqlInsertInto :: IdentInfo -> SqlExpr (Maybe (Entity a)) -> (Builder, [PersistValue])

type ToMaybeT (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToMaybe

type ToMaybeT (SqlExpr (Value a)) = SqlExpr (Value (Maybe (Nullable a)))

type ToMaybeT (SqlExpr (Entity a))

Defined in Database.Esqueleto.Experimental.ToMaybe

type ToMaybeT (SqlExpr (Entity a)) = SqlExpr (Maybe (Entity a))

type ToMaybeT (SqlExpr (Maybe a))

Defined in Database.Esqueleto.Experimental.ToMaybe

type ToMaybeT (SqlExpr (Maybe a)) = SqlExpr (Maybe a)