Safe Haskell	None
Language	Haskell2010

Database.Beam.Backend

Synopsis

module Database.Beam.Backend.Types
class (BeamBackend be, Monad m, MonadIO m, Sql92SanityCheck syntax) => MonadBeam syntax be handle m | m -> syntax be handle where

Documentation

module Database.Beam.Backend.Types

class (BeamBackend be, Monad m, MonadIO m, Sql92SanityCheck syntax) => MonadBeam syntax be handle m | m -> syntax be handle where Source #

A class that ties together a Sql syntax, backend, handle, and monad type.

Intuitively, this allows you to write code that performs database commands without having to know the underlying API. As long as you have an appropriate handle from a database library that Beam can use, you can use the MonadBeam methods to execute the query.

Provided here is a low-level interface. Most often, you'll only need the withDatabase and withDatabaseDebug function. The 'run*' functions are wrapped by the appropriate functions in Database.Beam.Query.

This interface is very high-level and isn't meant to expose the full power of the underlying database. Namely, it only supports simple data retrieval strategies. More complicated strategies (for example, Postgres's COPY) are supported in individual backends. See the documentation of those backends for more details.

Minimal complete definition

withDatabaseDebug, runReturningMany

Methods

withDatabaseDebug Source #

Arguments

:: (String -> IO ())	Database statement logging function
-> handle	The database connection handle against which to execute the action
-> m a	The database action
-> IO a

Run a database action, and log debugging information about statements executed using the specified IO action.

withDatabase :: handle -> m a -> IO a Source #

runReturningMany Source #

Arguments

:: FromBackendRow be x
=> syntax	The query to run
-> (m (Maybe x) -> m a)	Reader action that will be called with a function to fetch the next row
-> m a

Run a query determined by the given syntax, providing an action that will be called to consume the results from the database (if any). The action will get a reader action that can be used to fetch the next row. When this reader action returns Nothing, there are no rows left to consume. When the reader action returns, the database result is freed.

runNoReturn :: syntax -> m () Source #

Run the given command and don't consume any results. Useful for DML statements like INSERT, UPDATE, and DELETE, or DDL statements.

runReturningOne :: FromBackendRow be x => syntax -> m (Maybe x) Source #

Run the given command and fetch the unique result. The result is Nothing if either no results are returned or more than one result is returned.

runReturningList :: FromBackendRow be x => syntax -> m [x] Source #

Run the given command, collect all the results, and return them as a list. May be more convenient than runReturningMany, but reads the entire result set into memory.