esqueleto-2.4.1: Type-safe EDSL for SQL queries on persistent backends.

Safe Haskell | None
Language | Haskell98

Database.Esqueleto.Internal.Language

Contents

- The pretty face
- The guts

Description

This is an internal module, anything exported by this module may change without a major version bump. Please use only Database.Esqueleto if possible.

Synopsis

- class (Functor query, Applicative query, Monad query) => Esqueleto query expr backend | query -> expr backend, expr -> query backend where
  - fromStart :: (PersistEntity a, PersistEntityBackend a ~ backend) => query (expr (PreprocessedFrom (expr (Entity a))))
  - fromStartMaybe :: (PersistEntity a, PersistEntityBackend a ~ backend) => query (expr (PreprocessedFrom (expr (Maybe (Entity a)))))
  - fromJoin :: IsJoinKind join => expr (PreprocessedFrom a) -> expr (PreprocessedFrom b) -> query (expr (PreprocessedFrom (join a b)))
  - fromFinish :: expr (PreprocessedFrom a) -> query a
  - where_ :: expr (Value Bool) -> query ()
  - on :: expr (Value Bool) -> query ()
  - groupBy :: ToSomeValues expr a => a -> query ()
  - orderBy :: [expr OrderBy] -> query ()
  - asc :: PersistField a => expr (Value a) -> expr OrderBy
  - desc :: PersistField a => expr (Value a) -> expr OrderBy
  - limit :: Int64 -> query ()
  - offset :: Int64 -> query ()
  - distinct :: query a -> query a
  - distinctOn :: [expr DistinctOn] -> query a -> query a
  - don :: expr (Value a) -> expr DistinctOn
  - distinctOnOrderBy :: [expr OrderBy] -> query a -> query a
  - rand :: expr OrderBy
  - having :: expr (Value Bool) -> query ()
  - locking :: LockingKind -> query ()
  - sub_select :: PersistField a => query (expr (Value a)) -> expr (Value a)
  - sub_selectDistinct :: PersistField a => query (expr (Value a)) -> expr (Value a)
  - (^.) :: (PersistEntity val, PersistField typ) => expr (Entity val) -> EntityField val typ -> expr (Value typ)
  - (?.) :: (PersistEntity val, PersistField typ) => expr (Maybe (Entity val)) -> EntityField val typ -> expr (Value (Maybe typ))
  - val :: PersistField typ => typ -> expr (Value typ)
  - isNothing :: PersistField typ => expr (Value (Maybe typ)) -> expr (Value Bool)
  - just :: expr (Value typ) -> expr (Value (Maybe typ))
  - nothing :: expr (Value (Maybe typ))
  - joinV :: expr (Value (Maybe (Maybe typ))) -> expr (Value (Maybe typ))
  - countRows :: Num a => expr (Value a)
  - count :: Num a => expr (Value typ) -> expr (Value a)
  - countDistinct :: Num a => expr (Value typ) -> expr (Value a)
  - not_ :: expr (Value Bool) -> expr (Value Bool)
  - (==.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
  - (>=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
  - (>.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
  - (<=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
  - (<.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
  - (!=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
  - (&&.) :: expr (Value Bool) -> expr (Value Bool) -> expr (Value Bool)
  - (||.) :: expr (Value Bool) -> expr (Value Bool) -> expr (Value Bool)
  - (+.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
  - (-.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
  - (/.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
  - (*.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
  - random_ :: (PersistField a, Num a) => expr (Value a)
  - round_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
  - ceiling_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
  - floor_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
  - sum_ :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value (Maybe b))
  - min_ :: PersistField a => expr (Value a) -> expr (Value (Maybe a))
  - max_ :: PersistField a => expr (Value a) -> expr (Value (Maybe a))
  - avg_ :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value (Maybe b))
  - castNum :: (Num a, Num b) => expr (Value a) -> expr (Value b)
  - castNumM :: (Num a, Num b) => expr (Value (Maybe a)) -> expr (Value (Maybe b))
  - coalesce :: PersistField a => [expr (Value (Maybe a))] -> expr (Value (Maybe a))
  - coalesceDefault :: PersistField a => [expr (Value (Maybe a))] -> expr (Value a) -> expr (Value a)
  - lower_ :: SqlString s => expr (Value s) -> expr (Value s)
  - like :: SqlString s => expr (Value s) -> expr (Value s) -> expr (Value Bool)
  - ilike :: SqlString s => expr (Value s) -> expr (Value s) -> expr (Value Bool)
  - (%) :: SqlString s => expr (Value s)
  - concat_ :: SqlString s => [expr (Value s)] -> expr (Value s)
  - (++.) :: SqlString s => expr (Value s) -> expr (Value s) -> expr (Value s)
  - castString :: (SqlString s, SqlString r) => expr (Value s) -> expr (Value r)
  - subList_select :: PersistField a => query (expr (Value a)) -> expr (ValueList a)
  - subList_selectDistinct :: PersistField a => query (expr (Value a)) -> expr (ValueList a)
  - valList :: PersistField typ => [typ] -> expr (ValueList typ)
  - justList :: expr (ValueList typ) -> expr (ValueList (Maybe typ))
  - in_ :: PersistField typ => expr (Value typ) -> expr (ValueList typ) -> expr (Value Bool)
  - notIn :: PersistField typ => expr (Value typ) -> expr (ValueList typ) -> expr (Value Bool)
  - exists :: query () -> expr (Value Bool)
  - notExists :: query () -> expr (Value Bool)
  - set :: PersistEntity val => expr (Entity val) -> [expr (Update val)] -> query ()
  - (=.) :: (PersistEntity val, PersistField typ) => EntityField val typ -> expr (Value typ) -> expr (Update val)
  - (+=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val)
  - (-=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val)
  - (*=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val)
  - (/=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val)
  - (<#) :: (a -> b) -> expr (Value a) -> expr (Insertion b)
  - (<&>) :: expr (Insertion (a -> b)) -> expr (Value a) -> expr (Insertion b)
  - case_ :: PersistField a => [(expr (Value Bool), expr (Value a))] -> expr (Value a) -> expr (Value a)
- from :: From query expr backend a => (a -> query b) -> query b
- data Value a = Value a
- unValue :: Value a -> a
- data ValueList a = ValueList a
- data SomeValue expr where
  - SomeValue :: Esqueleto query expr backend => expr (Value a) -> SomeValue expr
- class ToSomeValues expr a where
  - toSomeValues :: a -> [SomeValue expr]
- data InnerJoin a b = a `InnerJoin` b
- data CrossJoin a b = a `CrossJoin` b
- data LeftOuterJoin a b = a `LeftOuterJoin` b
- data RightOuterJoin a b = a `RightOuterJoin` b
- data FullOuterJoin a b = a `FullOuterJoin` b
- data OnClauseWithoutMatchingJoinException = OnClauseWithoutMatchingJoinException String
- data OrderBy
- data DistinctOn
- data Update typ
- data Insertion a
- data LockingKind
  - = ForUpdate
  - | ForShare
  - | LockInShareMode
- class PersistField a => SqlString a
- data JoinKind
  - = InnerJoinKind
  - | CrossJoinKind
  - | LeftOuterJoinKind
  - | RightOuterJoinKind
  - | FullOuterJoinKind
- class IsJoinKind join where
  - smartJoin :: a -> b -> join a b
  - reifyJoinKind :: join a b -> JoinKind
- data PreprocessedFrom a
- class Esqueleto query expr backend => From query expr backend a
- class Esqueleto query expr backend => FromPreprocess query expr backend a
- when_ :: expr (Value Bool) -> () -> expr a -> (expr (Value Bool), expr a)
- then_ :: ()
- else_ :: expr a -> expr a

# The pretty face

class (Functor query, Applicative query, Monad query) => Esqueleto query expr backend | query -> expr backend, expr -> query backend where Source

Finally tagless representation of `esqueleto`'s EDSL.

Methods

fromStart :: (PersistEntity a, PersistEntityBackend a ~ backend) => query (expr (PreprocessedFrom (expr (Entity a)))) Source

(Internal) Start a `from` query with an entity. `from` does two kinds of magic using `fromStart`, `fromJoin` and `fromFinish`:

1. The simple but tedious magic of allowing tuples to be used.
2. The more advanced magic of creating `JOIN`s. The `JOIN` is processed from right to left. The rightmost entity of the `JOIN` is created with `fromStart`. Each `JOIN` step is then translated into a call to `fromJoin`. In the end, `fromFinish` is called to materialize the `JOIN`.

fromStartMaybe :: (PersistEntity a, PersistEntityBackend a ~ backend) => query (expr (PreprocessedFrom (expr (Maybe (Entity a))))) Source

(Internal) Same as `fromStart`, but entity may be missing.

fromJoin :: IsJoinKind join => expr (PreprocessedFrom a) -> expr (PreprocessedFrom b) -> query (expr (PreprocessedFrom (join a b))) Source

(Internal) Do a `JOIN`.

fromFinish :: expr (PreprocessedFrom a) -> query a Source

(Internal) Finish a `JOIN`.

where_ :: expr (Value Bool) -> query () Source

`WHERE` clause: restrict the query's result.

on :: expr (Value Bool) -> query () Source

`ON` clause: restrict the a `JOIN`'s result. The `ON` clause will be applied to the last `JOIN` that does not have an `ON` clause yet. If there are no `JOIN`s without `ON` clauses (either because you didn't do any `JOIN`, or because all `JOIN`s already have their own `ON` clauses), a runtime exception `OnClauseWithoutMatchingJoinException` is thrown. `ON` clauses are optional when doing `JOIN`s.

On the simple case of doing just one `JOIN`, for example

    select $
    from $ \(foo `InnerJoin` bar) -> do
      on (foo ^. FooId ==. bar ^. BarFooId)
      ...

there's no ambiguity and the rules above just mean that you're allowed to call `on` only once (as in SQL). If you have many joins, then the `on`s are applied on the reverse order that the `JOIN`s appear. For example:

    select $
    from $ \(foo `InnerJoin` bar `InnerJoin` baz) -> do
      on (baz ^. BazId ==. bar ^. BarBazId)
      on (foo ^. FooId ==. bar ^. BarFooId)
      ...

The order is reversed in order to improve composability. For example, consider `query1` and `query2` below:

    let query1 =
          from $ \(foo `InnerJoin` bar) -> do
            on (foo ^. FooId ==. bar ^. BarFooId)
        query2 =
          from $ \(mbaz `LeftOuterJoin` quux) -> do
            return (mbaz ?. BazName, quux)
        test1 =      (,) <$> query1 <*> query2
        test2 = flip (,) <$> query2 <*> query1

If the order was not reversed, then `test2` would be broken: `query1`'s `on` would refer to `query2`'s `LeftOuterJoin`.

groupBy :: ToSomeValues expr a => a -> query () Source

`GROUP BY` clause. You can enclose multiple columns in a tuple.

    select $ from \(foo `InnerJoin` bar) -> do
      on (foo ^. FooBarId ==. bar ^. BarId)
      groupBy (bar ^. BarId, bar ^. BarName)
      return (bar ^. BarId, bar ^. BarName, countRows)

With groupBy you can sort by aggregate functions, like so (we used `let` to restrict the more general `countRows` to `SqlExpr (Value Int)` to avoid ambiguity---the second use of `countRows` has its type restricted by the `:: Int` below):

    r <- select $ from \(foo `InnerJoin` bar) -> do
      on (foo ^. FooBarId ==. bar ^. BarId)
      groupBy $ bar ^. BarName
      let countRows' = countRows
      orderBy [asc countRows']
      return (bar ^. BarName, countRows')
    forM_ r $ \(Value name, Value count) -> do
      print name
      print (count :: Int)

orderBy :: [expr OrderBy] -> query () Source

`ORDER BY` clause. See also `asc` and `desc`.

Multiple calls to `orderBy` get concatenated on the final query, including `distinctOnOrderBy`.

asc :: PersistField a => expr (Value a) -> expr OrderBy Source

Ascending order of this field or expression.

desc :: PersistField a => expr (Value a) -> expr OrderBy Source

Descending order of this field or expression.

limit :: Int64 -> query () Source

`LIMIT`. Limit the number of returned rows.

offset :: Int64 -> query () Source

`OFFSET`. Usually used with `limit`.

distinct :: query a -> query a Source

`DISTINCT`. Change the current `SELECT` into `SELECT DISTINCT`. For example:

    select $ distinct $
      from \foo -> do
      ...

Note that this also has the same effect:

    select $
      from \foo -> do
      distinct (return ())
      ...

Since: 2.2.4

distinctOn :: [expr DistinctOn] -> query a -> query a Source

`DISTINCT ON`. Change the current `SELECT` into `SELECT DISTINCT ON (expressions)`. For example:

    select $
      from \foo ->
      distinctOn [don (foo ^. FooName), don (foo ^. FooState)] $ do
      ...

You can also chain different calls to `distinctOn`. The above is equivalent to:

    select $
      from \foo ->
      distinctOn [don (foo ^. FooName)] $
      distinctOn [don (foo ^. FooState)] $ do
      ...

Each call to `distinctOn` adds more expressions. Calls to `distinctOn` override any calls to `distinct`.

Note that PostgreSQL requires the expressions on `DISTINCT ON` to be the first ones to appear on a `ORDER BY`. This is not managed automatically by esqueleto, keeping its spirit of trying to be close to raw SQL.

Supported by PostgreSQL only.

Since: 2.2.4

don :: expr (Value a) -> expr DistinctOn Source

Erase an expression's type so that it's suitable to be used by `distinctOn`.

Since: 2.2.4

distinctOnOrderBy :: [expr OrderBy] -> query a -> query a Source

A convenience function that calls both `distinctOn` and `orderBy`. In other words,

    distinctOnOrderBy [asc foo, desc bar, desc quux] $ do
      ...

is the same as:

    distinctOn [don foo, don  bar, don  quux] $ do
      orderBy  [asc foo, desc bar, desc quux]
      ...

Since: 2.2.4

rand :: expr OrderBy Source

`ORDER BY random()` clause.

Since: 1.3.10

having :: expr (Value Bool) -> query () Source

`HAVING`.

Since: 1.2.2

locking :: LockingKind -> query () Source

Add a locking clause to the query. Please read `LockingKind` documentation and your RDBMS manual.

If multiple calls to `locking` are made on the same query, the last one is used.

Since: 2.2.7

sub_select :: PersistField a => query (expr (Value a)) -> expr (Value a) Source

Execute a subquery `SELECT` in an expression. Returns a simple value so should be used only when the `SELECT` query is guaranteed to return just one row.

sub_selectDistinct :: PersistField a => query (expr (Value a)) -> expr (Value a) Source

Deprecated: Since 2.2.4: use `sub_select` and `distinct`.

Same as `sub_select` but using `SELECT DISTINCT`.

(^.) :: (PersistEntity val, PersistField typ) => expr (Entity val) -> EntityField val typ -> expr (Value typ) infixl 9 Source

Project a field of an entity.

(?.) :: (PersistEntity val, PersistField typ) => expr (Maybe (Entity val)) -> EntityField val typ -> expr (Value (Maybe typ)) Source

Project a field of an entity that may be null.

val :: PersistField typ => typ -> expr (Value typ) Source

Lift a constant value from Haskell-land to the query.

isNothing :: PersistField typ => expr (Value (Maybe typ)) -> expr (Value Bool) Source

`IS NULL` comparison.

just :: expr (Value typ) -> expr (Value (Maybe typ)) Source

Analogous to `Just`, promotes a value of type `typ` into one of type `Maybe typ`. It should hold that ``val` . Just === just . `val``.

nothing :: expr (Value (Maybe typ)) Source

`NULL` value.

joinV :: expr (Value (Maybe (Maybe typ))) -> expr (Value (Maybe typ)) Source

Join nested `Maybe`s in a `Value` into one. This is useful when calling aggregate functions on nullable fields.

countRows :: Num a => expr (Value a) Source

`COUNT(*)` value.

count :: Num a => expr (Value typ) -> expr (Value a) Source

`COUNT`.

countDistinct :: Num a => expr (Value typ) -> expr (Value a) Source

`COUNT(DISTINCT x)`.

Since: 2.4.1

not_ :: expr (Value Bool) -> expr (Value Bool) Source

(==.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool) infix 4 Source

(>=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool) infix 4 Source

(>.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool) infix 4 Source

(<=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool) infix 4 Source

(<.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool) infix 4 Source

(!=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool) infix 4 Source

(&&.) :: expr (Value Bool) -> expr (Value Bool) -> expr (Value Bool) infixr 3 Source

(||.) :: expr (Value Bool) -> expr (Value Bool) -> expr (Value Bool) infixr 2 Source

(+.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a) infixl 6 Source

(-.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a) infixl 6 Source

(/.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a) infixl 7 Source

(*.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a) infixl 7 Source

random_ :: (PersistField a, Num a) => expr (Value a) Source

round_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b) Source

ceiling_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b) Source

floor_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b) Source

sum_ :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value (Maybe b)) Source

min_ :: PersistField a => expr (Value a) -> expr (Value (Maybe a)) Source

max_ :: PersistField a => expr (Value a) -> expr (Value (Maybe a)) Source

avg_ :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value (Maybe b)) Source

castNum :: (Num a, Num b) => expr (Value a) -> expr (Value b) Source

Allow a number of one type to be used as one of another type via an implicit cast. An explicit cast is not made, this function changes only the types on the Haskell side.

Caveat: Trying to use `castNum` from `Double` to `Int` will not result in an integer, the original fractional number will still be used! Use `round_`, `ceiling_` or `floor_` instead.

Safety: This operation is mostly safe due to the `Num` constraint between the types and the fact that RDBMSs usually allow numbers of different types to be used interchangeably. However, there may still be issues with the query not being accepted by the RDBMS or `persistent` not being able to parse it.

Since: 2.2.9

castNumM :: (Num a, Num b) => expr (Value (Maybe a)) -> expr (Value (Maybe b)) Source

Same as `castNum`, but for nullable values.

Since: 2.2.9

coalesce :: PersistField a => [expr (Value (Maybe a))] -> expr (Value (Maybe a)) Source

`COALESCE` function. Evaluates the arguments in order and returns the value of the first non-NULL expression, or NULL (Nothing) otherwise. Some RDBMSs (such as SQLite) require at least two arguments; please refer to the appropriate documentation.

Since: 1.4.3

coalesceDefault :: PersistField a => [expr (Value (Maybe a))] -> expr (Value a) -> expr (Value a) Source

Like `coalesce`, but takes a non-nullable expression placed at the end of the expression list, which guarantees a non-NULL result.

Since: 1.4.3

lower_ :: SqlString s => expr (Value s) -> expr (Value s) Source

`LOWER` function.

like :: SqlString s => expr (Value s) -> expr (Value s) -> expr (Value Bool) infixr 2 Source

`LIKE` operator.

ilike :: SqlString s => expr (Value s) -> expr (Value s) -> expr (Value Bool) infixr 2 Source

`ILIKE` operator (case-insensitive `LIKE`).

Supported by PostgreSQL only.

Since: 2.2.3

(%) :: SqlString s => expr (Value s) Source

The string ``%``. May be useful while using `like` and concatenation (`concat_` or `++.`, depending on your database). Note that you always to type the parenthesis, for example:

    name `like` (%) ++. val "John" ++. (%)

concat_ :: SqlString s => [expr (Value s)] -> expr (Value s) Source

The `CONCAT` function with a variable number of parameters. Supported by MySQL and PostgreSQL.

(++.) :: SqlString s => expr (Value s) -> expr (Value s) -> expr (Value s) infixr 5 Source

The `||` string concatenation operator (named after Haskell's `++` in order to avoid naming clash with `||.`). Supported by SQLite and PostgreSQL.

castString :: (SqlString s, SqlString r) => expr (Value s) -> expr (Value r) Source

Cast a string type into `Text`. This function is very useful if you want to use `newtype`s, or if you want to apply functions such as `like` to strings of different types.

Safety: This is a slightly unsafe function, especially if you have defined your own instances of `SqlString`. Also, since `Maybe` is an instance of `SqlString`, it's possible to turn a nullable value into a non-nullable one. Avoid using this function if possible.

subList_select :: PersistField a => query (expr (Value a)) -> expr (ValueList a) Source

Execute a subquery `SELECT` in an expression. Returns a list of values.

subList_selectDistinct :: PersistField a => query (expr (Value a)) -> expr (ValueList a) Source

Deprecated: Since 2.2.4: use `subList_select` and `distinct`.

Same as `sublist_select` but using `SELECT DISTINCT`.

valList :: PersistField typ => [typ] -> expr (ValueList typ) Source

Lift a list of constant value from Haskell-land to the query.

justList :: expr (ValueList typ) -> expr (ValueList (Maybe typ)) Source

Same as `just` but for `ValueList`. Most of the time you won't need it, though, because you can use `just` from inside `subList_select` or `Just` from inside `valList`.

Since: 2.2.12

in_ :: PersistField typ => expr (Value typ) -> expr (ValueList typ) -> expr (Value Bool) Source

`IN` operator.

notIn :: PersistField typ => expr (Value typ) -> expr (ValueList typ) -> expr (Value Bool) Source

`NOT IN` operator.

exists :: query () -> expr (Value Bool) Source

`EXISTS` operator. For example:

    select $
    from $ \person -> do
    where_ $ exists $
             from $ \post -> do
             where_ (post ^. BlogPostAuthorId ==. person ^. PersonId)
    return person

notExists :: query () -> expr (Value Bool) Source

`NOT EXISTS` operator.

set :: PersistEntity val => expr (Entity val) -> [expr (Update val)] -> query () Source

`SET` clause used on `UPDATE`s. Note that while it's not a type error to use this function on a `SELECT`, it will most certainly result in a runtime error.

(=.) :: (PersistEntity val, PersistField typ) => EntityField val typ -> expr (Value typ) -> expr (Update val) infixr 3 Source

(+=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val) infixr 3 Source

(-=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val) infixr 3 Source

(*=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val) infixr 3 Source

(/=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val) infixr 3 Source

(<#) :: (a -> b) -> expr (Value a) -> expr (Insertion b) Source

Apply a `PersistField` constructor to `expr Value` arguments.

(<&>) :: expr (Insertion (a -> b)) -> expr (Value a) -> expr (Insertion b) Source

Apply extra `expr Value` arguments to a `PersistField` constructor

case_ :: PersistField a => [(expr (Value Bool), expr (Value a))] -> expr (Value a) -> expr (Value a) Source

`CASE` statement. For example:

    select $
    return $
    case_
       [ when_
           (exists $
           from $ \p -> do
           where_ (p ^. PersonName ==. val "Mike"))
         then_
           (sub_select $
           from $ \v -> do
           let sub =
                   from $ \c -> do
                   where_ (c ^. PersonName ==. val "Mike")
                   return (c ^. PersonFavNum)
           where_ (v ^. PersonFavNum >. sub_select sub)
           return $ count (v ^. PersonName) +. val (1 :: Int)) ]
       (else_ $ val (-1))

This query is a bit complicated, but basically it checks if a person named `"Mike"` exists, and if that person does, run the subquery to find out how many people have a ranking (by Fav Num) higher than `"Mike"`.

NOTE: There are a few things to be aware about this statement.

- This only implements the full CASE statement, it does not implement the "simple" CASE statement.
- At least one `when_` and `then_` is mandatory otherwise it will emit an error.
- The `else_` is also mandatory, unlike the SQL statement in which if the `ELSE` is omitted it will return a `NULL`. You can reproduce this via `nothing`.

Since: 2.1.2

Instances

Esqueleto SqlQuery SqlExpr SqlBackend Source |

from :: From query expr backend a => (a -> query b) -> query b Source

`FROM` clause: bring entities into scope.

This function internally uses two type classes in order to provide some flexibility of how you may call it. Internally we refer to these type classes as the two different magics.

The innermost magic allows you to use `from` with the following types:

- `expr (Entity val)`, which brings a single entity into scope.
- `expr (Maybe (Entity val))`, which brings a single entity that may be `NULL` into scope. Used for `OUTER JOIN`s.
- A `JOIN` of any other two types allowed by the innermost magic, where a `JOIN` may be an `InnerJoin`, a `CrossJoin`, a `LeftOuterJoin`, a `RightOuterJoin`, or a `FullOuterJoin`. The `JOINs` have left fixity.

The outermost magic allows you to use `from` on any tuples of types supported by innermost magic (and also tuples of tuples, and so on), up to 8-tuples.

Note that using `from` for the same entity twice does work and corresponds to a self-join. You don't even need to use two different calls to `from`, you may use a `JOIN` or a tuple.

The following are valid examples of uses of `from` (the types of the arguments of the lambda are inside square brackets):

    from $ \person -> ...
    from $ \(person, blogPost) -> ...
    from $ \(p `LeftOuterJoin` mb) -> ...
    from $ \(p1 `InnerJoin` f `InnerJoin` p2) -> ...
    from $ \((p1 `InnerJoin` f) `InnerJoin` p2) -> ...

The types of the arguments to the lambdas above are, respectively:

    person
      :: ( Esqueleto query expr backend
         , PersistEntity Person
         , PersistEntityBackend Person ~ backend
         ) => expr (Entity Person)
    (person, blogPost)
      :: (...) => (expr (Entity Person), expr (Entity BlogPost))
    (p `LeftOuterJoin` mb)
      :: (...) => InnerJoin (expr (Entity Person)) (expr (Maybe (Entity BlogPost)))
    (p1 `InnerJoin` f `InnerJoin` p2)
      :: (...) => InnerJoin
                    (InnerJoin (expr (Entity Person))
                               (expr (Entity Follow)))
                    (expr (Entity Person))
    (p1 `InnerJoin` (f `InnerJoin` p2)) ::
      :: (...) => InnerJoin
                    (expr (Entity Person))
                    (InnerJoin (expr (Entity Follow))
                               (expr (Entity Person)))

Note that some backends may not support all kinds of `JOIN`s.

data Value a Source

A single value (as opposed to a whole entity). You may use `(`^.`)` or `(`?.`)` to get a `Value` from an `Entity`.

Constructors

Value a |

Instances

Functor Value Source | Since: 1.4.4
ToSomeValues SqlExpr (SqlExpr (Value a)) Source |
Eq a => Eq (Value a) Source |
Ord a => Ord (Value a) Source |
Show a => Show (Value a) Source |
PersistField a => SqlSelect (SqlExpr (Value a)) (Value a) Source | You may return any single value (i.e. a single column) from a `select` query.

unValue :: Value a -> a Source

Unwrap a `Value`.

Since: 1.4.1

data ValueList a Source

A list of single values. There's a limited set of functions able to work with this data type (such as `subList_select`, `valList`, `in_` and `exists`).

Constructors

ValueList a |

Instances

Eq a => Eq (ValueList a) Source |
Ord a => Ord (ValueList a) Source |
Show a => Show (ValueList a) Source |

data SomeValue expr where Source

A wrapper type for for any `expr (Value a)` for all a.

Constructors

SomeValue :: Esqueleto query expr backend => expr (Value a) -> SomeValue expr |

class ToSomeValues expr a where Source

A class of things that can be converted into a list of SomeValue. It has instances for tuples and is the reason why `groupBy` can take tuples, like ``groupBy` (foo `^.` FooId, foo `^.` FooName, foo `^.` FooType)`.

Methods

toSomeValues :: a -> [SomeValue expr] Source

Instances

ToSomeValues SqlExpr (SqlExpr (Value a)) Source |
(ToSomeValues expr a, ToSomeValues expr b) => ToSomeValues expr (a, b) Source |
(ToSomeValues expr a, ToSomeValues expr b, ToSomeValues expr c) => ToSomeValues expr (a, b, c) Source |
(ToSomeValues expr a, ToSomeValues expr b, ToSomeValues expr c, ToSomeValues expr d) => ToSomeValues expr (a, b, c, d) Source |
(ToSomeValues expr a, ToSomeValues expr b, ToSomeValues expr c, ToSomeValues expr d, ToSomeValues expr e) => ToSomeValues expr (a, b, c, d, e) Source |
(ToSomeValues expr a, ToSomeValues expr b, ToSomeValues expr c, ToSomeValues expr d, ToSomeValues expr e, ToSomeValues expr f) => ToSomeValues expr (a, b, c, d, e, f) Source |
(ToSomeValues expr a, ToSomeValues expr b, ToSomeValues expr c, ToSomeValues expr d, ToSomeValues expr e, ToSomeValues expr f, ToSomeValues expr g) => ToSomeValues expr (a, b, c, d, e, f, g) Source |
(ToSomeValues expr a, ToSomeValues expr b, ToSomeValues expr c, ToSomeValues expr d, ToSomeValues expr e, ToSomeValues expr f, ToSomeValues expr g, ToSomeValues expr h) => ToSomeValues expr (a, b, c, d, e, f, g, h) Source |

data InnerJoin a b infixl 2 Source

Data type that represents an `INNER JOIN` (see `LeftOuterJoin` for an example).

Constructors

a `InnerJoin` b infixl 2 |

Instances

IsJoinKind InnerJoin Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (InnerJoin a b)) => From query expr backend (InnerJoin a b) Source |

data CrossJoin a b infixl 2 Source

Data type that represents a `CROSS JOIN` (see `LeftOuterJoin` for an example).

Constructors

a `CrossJoin` b infixl 2 |

Instances

IsJoinKind CrossJoin Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (CrossJoin a b)) => From query expr backend (CrossJoin a b) Source |

data LeftOuterJoin a b infixl 2 Source

Data type that represents a `LEFT OUTER JOIN`. For example,

    select $
    from $ \(person `LeftOuterJoin` pet) ->
      ...

is translated into

    SELECT ...
    FROM Person LEFT OUTER JOIN Pet
    ...

See also: `from`.

Constructors

a `LeftOuterJoin` b infixl 2 |

Instances

IsJoinKind LeftOuterJoin Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (LeftOuterJoin a b)) => From query expr backend (LeftOuterJoin a b) Source |

data RightOuterJoin a b infixl 2 Source

Data type that represents a `RIGHT OUTER JOIN` (see `LeftOuterJoin` for an example).

Constructors

a `RightOuterJoin` b infixl 2 |

Instances

IsJoinKind RightOuterJoin Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (RightOuterJoin a b)) => From query expr backend (RightOuterJoin a b) Source |

data FullOuterJoin a b infixl 2 Source

Data type that represents a `FULL OUTER JOIN` (see `LeftOuterJoin` for an example).

Constructors

a `FullOuterJoin` b infixl 2 |

Instances

IsJoinKind FullOuterJoin Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (FullOuterJoin a b)) => From query expr backend (FullOuterJoin a b) Source |

data OnClauseWithoutMatchingJoinException Source

Exception thrown whenever `on` is used to create an `ON` clause but no matching `JOIN` is found.

Constructors

OnClauseWithoutMatchingJoinException String |

Instances

Eq OnClauseWithoutMatchingJoinException Source |
Ord OnClauseWithoutMatchingJoinException Source |
Show OnClauseWithoutMatchingJoinException Source |
Exception OnClauseWithoutMatchingJoinException Source |

data OrderBy Source

Phantom type used by `orderBy`, `asc` and `desc`.

data DistinctOn Source

Phantom type used by `distinctOn` and `don`.

data Update typ Source

Phantom type for a `SET` operation on an entity of the given type (see `set` and '(=.)').

data Insertion a Source

Phantom type used by `insertSelect`.

data LockingKind Source

Different kinds of locking clauses supported by `locking`.

Note that each RDBMS has different locking support. The constructors of this datatype specify only the syntax of the locking mechanism, not its semantics. For example, even though both MySQL and PostgreSQL support `ForUpdate`, there are no guarantees that they will behave the same.

Since: 2.2.7

Constructors

ForUpdate | `FOR UPDATE` syntax. Supported by MySQL, Oracle and PostgreSQL. Since: 2.2.7
ForShare | `FOR SHARE` syntax. Supported by PostgreSQL. Since: 2.2.7
LockInShareMode | `LOCK IN SHARE MODE` syntax. Supported by MySQL. Since: 2.2.7

class PersistField a => SqlString a Source

Phantom class of data types that are treated as strings by the RDBMS. It has no methods because it's only used to avoid type errors such as trying to concatenate integers.

If you have a custom data type or `newtype`, feel free to make it an instance of this class.

Since: 2.4.0

Instances

SqlString ByteString Source | Since: 2.3.0
SqlString Html Source | Since: 2.3.0
SqlString Text Source | Since: 2.3.0
SqlString Text Source | Since: 2.3.0
(~) * a Char => SqlString [a] Source | Since: 2.3.0
SqlString a => SqlString (Maybe a) Source | Since: 2.4.0

# The guts

data JoinKind Source

(Internal) A kind of `JOIN`.

Constructors

InnerJoinKind

    INNER JOIN

CrossJoinKind

    CROSS JOIN

LeftOuterJoinKind

    LEFT OUTER JOIN

RightOuterJoinKind

    RIGHT OUTER JOIN

FullOuterJoinKind

    FULL OUTER JOIN

Instances

Eq JoinKind Source |

class IsJoinKind join where Source

(Internal) Functions that operate on types (that should be) of kind `JoinKind`.

Methods

smartJoin :: a -> b -> join a b Source

(Internal) `smartJoin a b` is a `JOIN` of the correct kind.

reifyJoinKind :: join a b -> JoinKind Source

(Internal) Reify a `JoinKind` from a `JOIN`. This function is non-strict.

Instances

IsJoinKind FullOuterJoin Source |
IsJoinKind RightOuterJoin Source |
IsJoinKind LeftOuterJoin Source |
IsJoinKind CrossJoin Source |
IsJoinKind InnerJoin Source |

data PreprocessedFrom a Source

(Internal) Phantom type used to process `from` (see `fromStart`).

class Esqueleto query expr backend => From query expr backend a Source

(Internal) Class that implements the tuple `from` magic (see `fromStart`).

Minimal complete definition

from_

Instances

(Esqueleto query expr backend, FromPreprocess query expr backend (expr (Maybe (Entity val)))) => From query expr backend (expr (Maybe (Entity val))) Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (expr (Entity val))) => From query expr backend (expr (Entity val)) Source |
(From query expr backend a, From query expr backend b) => From query expr backend (a, b) Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (FullOuterJoin a b)) => From query expr backend (FullOuterJoin a b) Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (RightOuterJoin a b)) => From query expr backend (RightOuterJoin a b) Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (LeftOuterJoin a b)) => From query expr backend (LeftOuterJoin a b) Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (CrossJoin a b)) => From query expr backend (CrossJoin a b) Source |
(Esqueleto query expr backend, FromPreprocess query expr backend (InnerJoin a b)) => From query expr backend (InnerJoin a b) Source |
(From query expr backend a, From query expr backend b, From query expr backend c) => From query expr backend (a, b, c) Source |
(From query expr backend a, From query expr backend b, From query expr backend c, From query expr backend d) => From query expr backend (a, b, c, d) Source |
(From query expr backend a, From query expr backend b, From query expr backend c, From query expr backend d, From query expr backend e) => From query expr backend (a, b, c, d, e) Source |
(From query expr backend a, From query expr backend b, From query expr backend c, From query expr backend d, From query expr backend e, From query expr backend f) => From query expr backend (a, b, c, d, e, f) Source |
(From query expr backend a, From query expr backend b, From query expr backend c, From query expr backend d, From query expr backend e, From query expr backend f, From query expr backend g) => From query expr backend (a, b, c, d, e, f, g) Source |
(From query expr backend a, From query expr backend b, From query expr backend c, From query expr backend d, From query expr backend e, From query expr backend f, From query expr backend g, From query expr backend h) => From query expr backend (a, b, c, d, e, f, g, h) Source |

class Esqueleto query expr backend => FromPreprocess query expr backend a Source

(Internal) Class that implements the `JOIN` `from` magic (see `fromStart`).

Minimal complete definition

fromPreprocess

Instances

(Esqueleto query expr backend, PersistEntity val, (~) * (PersistEntityBackend val) backend) => FromPreprocess query expr backend (expr (Maybe (Entity val))) Source |
(Esqueleto query expr backend, PersistEntity val, (~) * (PersistEntityBackend val) backend) => FromPreprocess query expr backend (expr (Entity val)) Source |
(Esqueleto query expr backend, FromPreprocess query expr backend a, FromPreprocess query expr backend b, IsJoinKind join) => FromPreprocess query expr backend (join a b) Source |

when_ :: expr (Value Bool) -> () -> expr a -> (expr (Value Bool), expr a) Source

Syntax sugar for `case_`.

Since: 2.1.2

then_ :: () Source

Syntax sugar for `case_`.

Since: 2.1.2

else_ :: expr a -> expr a Source

Syntax sugar for `case_`.

Since: 2.1.2