Snap Extension for HDBC

This package provides an HDBC connection that can be used as part of the state in a Snap application.

This API is currently a work in progress, and should not be considered stable.

In order to use an HDBC connection, you may want to use one of the following packages which simply export the appropriate initializers:

• snap-extension-hdbc-odbc
• snap-extension-hdbc-postgresql
• snap-extension-hdbc-sqlite3

Example

If you want to use this as part of your Snap application, you should change your ApplicationState to contain the HDBCState, the following will be typically placed in the Application.hs file:

type Application = SnapExtend ApplicationState


data ApplicationState = ApplicationState
    { hdbcState     :: HDBCState
    }

In addition, you should provide an instance of HasHDBCState for your application:

instance HasHDBCState ApplicationState where
  getHDBCState     = hdbcState
  setHDBCState s a = a { hdbcState = s }

Finally, you should tell Snap how to initialize your state. This part is specific to the backend implementation you are using, where the type of hdbcInitializer depends on the package you have imported. For example, if you have imported Snap.Extension.HDBC.Sqlite3 then you could set things up with the following code:

applicationInitializer :: Initializer ApplicationState
applicationInitializer = do
    hdbc <- hdbcInitializer "resources/test1.db"
    return $ ApplicationState hdbc

The following code shows how you can access a connection to your database using the connWrapper function that is exported from this package:

type Application = SnapExtend ApplicationState

indexR :: Application ()
indexR = ifTop $ do
  conn <- connWrapper
  as <- liftIO $ liftM (map fst) $ describeTable conn "users"
  ts <- liftIO $ liftM (map (map fromSql)) $ quickQuery' conn "SELECT * FROM users" []
  ...