Database.Esqueleto.Internal.Sql

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

The pretty face

data SqlQuery a

SQL backend for esqueleto using SqlPersist.

Instances

Monad SqlQuery

Functor SqlQuery

Applicative SqlQuery

Esqueleto SqlQuery SqlExpr SqlPersist

data SqlExpr a

An expression on the SQL backend.

Instances

Esqueleto SqlQuery SqlExpr SqlPersist

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

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

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

You may return an Entity from a select query.

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

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

select :: (SqlSelect a r, MonadLogger m, MonadResourceBase m) => SqlQuery a -> SqlPersist m [r]

Execute an esqueleto SELECT query inside persistent's SqlPersist monad and return a list of rows.

We've seen that from has some magic about which kinds of things you may bring into scope. This select function also has some magic for which kinds of things you may bring back to Haskell-land by using SqlQuery's return:

• You may return a SqlExpr (Entity v) for an entity v (i.e., like the * in SQL), which is then returned to Haskell-land as just Entity v.
• You may return a SqlExpr (Maybe (Entity v)) for an entity v that may be NULL, which is then returned to Haskell-land as Maybe (Entity v). Used for OUTER JOINs.
• You may return a SqlExpr (Value t) for a value t (i.e., a single column), where t is any instance of PersistField, which is then returned to Haskell-land as Value t. You may use Value to return projections of an Entity (see (^.) and (?.)) or to return any other value calculated on the query (e.g., countRows or sub_select).

The SqlSelect a r class has functional dependencies that allow type information to flow both from a to r and vice-versa. This means that you'll almost never have to give any type signatures for esqueleto queries. For example, the query select $ from $ \p -> return p alone is ambiguous, but in the context of

 do ps <- select $
          from $ \p ->
          return p
    liftIO $ mapM_ (putStrLn . personName . entityVal) ps

we are able to infer from that single personName . entityVal function composition that the p inside the query is of type SqlExpr (Entity Person).

selectSource :: (SqlSelect a r, MonadLogger m, MonadResourceBase m) => SqlQuery a -> SqlPersist m (Source (ResourceT (SqlPersist m)) r)

Execute an esqueleto SELECT query inside persistent's SqlPersist monad and return a Source of rows.

selectDistinct :: (SqlSelect a r, MonadLogger m, MonadResourceBase m) => SqlQuery a -> SqlPersist m [r]

Execute an esqueleto SELECT DISTINCT query inside persistent's SqlPersist monad and return a list of rows.

selectDistinctSource :: (SqlSelect a r, MonadLogger m, MonadResourceBase m) => SqlQuery a -> SqlPersist m (Source (ResourceT (SqlPersist m)) r)

Execute an esqueleto SELECT DISTINCT query inside persistent's SqlPersist monad and return a Source of rows.

delete :: (MonadLogger m, MonadResourceBase m) => SqlQuery () -> SqlPersist m ()

Execute an esqueleto DELETE query inside persistent's SqlPersist monad. Note that currently there are no type checks for statements that should not appear on a DELETE query.

Example of usage:

 delete $
 from $ \appointment ->
 where_ (appointment ^. AppointmentDate <. val now)

Unlike select, there is a useful way of using delete that will lead to type ambiguities. If you want to delete all rows (i.e., no where_ clause), you'll have to use a type signature:

 delete $
 from $ \(appointment :: SqlExpr (Entity Appointment)) ->
 return ()

update :: (MonadLogger m, MonadResourceBase m, PersistEntity val, PersistEntityBackend val ~ SqlPersist) => (SqlExpr (Entity val) -> SqlQuery ()) -> SqlPersist m ()

Execute an esqueleto UPDATE query inside persistent's SqlPersist monad. Note that currently there are no type checks for statements that should not appear on a UPDATE query.

Example of usage:

 update $ p -> do
 set p [ PersonAge =. just (val thisYear) -. p ^. PersonBorn ]
 where_ $ isNull (p ^. PersonAge)

The guts

rawSelectSource :: (SqlSelect a r, MonadLogger m, MonadResourceBase m) => Mode -> SqlQuery a -> SqlPersist m (Source (ResourceT (SqlPersist m)) r)

(Internal) Execute an esqueleto SELECT SqlQuery inside persistent's SqlPersist monad.

runSource :: MonadResourceBase m => Source (ResourceT (SqlPersist m)) r -> SqlPersist m [r]

(Internal) Run a Source of rows.

rawExecute :: (MonadLogger m, MonadResourceBase m) => Mode -> SqlQuery () -> SqlPersist m ()

(Internal) Execute an esqueleto statement inside persistent's SqlPersist monad.

toRawSql :: SqlSelect a r => Mode -> Escape -> SqlQuery a -> (Builder, [PersistValue])

(Internal) Pretty prints a SqlQuery into a SQL query.

Note: if you're curious about the SQL query being generated by esqueleto, instead of manually using this function (which is possible but tedious), you may just turn on query logging of persistent.

data Mode

(Internal) Mode of query being converted by toRawSql.

Constructors

SELECT

SELECT_DISTINCT

DELETE

UPDATE

type Escape = DBName -> Builder

(Internal) Backend-specific function that escapes a DBName.

class SqlSelect a r | a -> r, r -> a

(Internal) Class for mapping results coming from SqlQuery into actual results.

This looks very similar to RawSql, and it is! However, there are some crucial differences and ultimately they're different classes.

Instances

SqlSelect () ()

Not useful for select, but used for update and delete.

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

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

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

You may return an Entity from a select query.

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

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

(SqlSelect a ra, SqlSelect b rb) => SqlSelect (a, b) (ra, rb)

You may return tuples (up to 8-tuples) and tuples of tuples from a select query.

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc) => SqlSelect (a, b, c) (ra, rb, rc)

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd) => SqlSelect (a, b, c, d) (ra, rb, rc, rd)

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re) => SqlSelect (a, b, c, d, e) (ra, rb, rc, rd, re)

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf) => SqlSelect (a, b, c, d, e, f) (ra, rb, rc, rd, re, rf)

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg) => SqlSelect (a, b, c, d, e, f, g) (ra, rb, rc, rd, re, rf, rg)

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh) => SqlSelect (a, b, c, d, e, f, g, h) (ra, rb, rc, rd, re, rf, rg, rh)