| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Database.Beam.Backend
- module Database.Beam.Backend.Types
- class (BeamBackend be, Monad m, MonadIO m, Sql92SanityCheck syntax) => MonadBeam syntax be handle m | m -> syntax be handle, be -> m, handle -> m 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, be -> m, handle -> m where Source #
A class that ties together a Sql syntax, backend, handle, and monad type.
Functional dependencies mean that only the backend type or the handle need to be specified.
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 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
Methods
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 #
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.