Opaleye.RunSelect

Documentation

runSelect

Arguments

:: Default FromFields fields haskells

=> Connection

-> Select fields

-> IO [haskells]

runSelect's use of the Default typeclass means that the compiler will have trouble inferring types. It is strongly recommended that you provide full type signatures when using runSelect.

Example type specialization:

runSelect :: Select (Field SqlInt4, Field SqlText) -> IO [(Int, String)]

Assuming the makeAdaptorAndInstance splice has been run for the product type Foo:

runSelect :: Select (Foo (Field SqlInt4) (Field SqlText) (Field SqlBool)
          -> IO [Foo Int String Bool]

runSelectTF

Arguments

:: Default FromFields (rec O) (rec H)

=> Connection

-> Select (rec O)

-> IO [rec H]

runSelectTF has better type inference than runSelect but only works with "higher-kinded data" types.

runSelectFold

Arguments

:: Default FromFields fields haskells

=> Connection

-> Select fields

-> b

-> (b -> haskells -> IO b)

-> IO b

runSelectFold streams the results of a query incrementally and consumes the results with a left fold.

This fold is not strict. The stream consumer is responsible for forcing the evaluation of its result to avoid space leaks.

declareCursor

Arguments

:: Default FromFields fields haskells

=> Connection

-> Select fields

-> IO (Cursor haskells)

Declare a temporary cursor. The cursor is given a unique name for the given connection.

Returns Nothing when the query returns zero rows.

closeCursor :: Cursor fields -> IO ()

Close the given cursor.

foldForward

Arguments

:: Cursor haskells

-> Int

-> (a -> haskells -> IO a)

-> a

-> IO (Either a a)

Fold over a chunk of rows, calling the supplied fold-like function on each row as it is received. In case the cursor is exhausted, a Left value is returned, otherwise a Right value is returned.

unsafeFromField :: (b -> b') -> FromField sqlType b -> FromField sqlType' b'

Use unsafeFromField to make an instance to allow you to run queries on your own datatypes. For example:

newtype Foo = Foo Int

instance QueryRunnerColumnDefault Foo Foo where
   defaultFromField = unsafeFromField Foo defaultFromField

It is "unsafe" because it does not check that the sqlType correctly corresponds to the Haskell type.

runSelectExplicit :: FromFields fields haskells -> Connection -> Select fields -> IO [haskells]

runSelectFoldExplicit :: FromFields fields haskells -> Connection -> Select fields -> b -> (b -> haskells -> IO b) -> IO b

declareCursorExplicit :: FromFields fields haskells -> Connection -> Select fields -> IO (Cursor haskells)

Datatypes

data Cursor haskells

Cursor within a transaction.

type FromFields = QueryRunner

type FromField = QueryRunnerColumn