{- | Module : Database.HDBC.Types Copyright : Copyright (C) 2005-2011 John Goerzen License : BSD3 Maintainer : John Goerzen <jgoerzen@complete.org> Stability : provisional Portability: portable Types for HDBC. Please note: this module is intended for authors of database driver libraries only. Authors of applications using HDBC should use 'Database.HDBC' exclusively. Written by John Goerzen, jgoerzen\@complete.org -} module Database.HDBC.Types (IConnection(..), Statement(..), SqlError(..), nToSql, iToSql, posixToSql, fromSql, safeFromSql, toSql, SqlValue(..), ConnWrapper(..), withWConn ) where import Database.HDBC.Statement import Database.HDBC.ColTypes import Control.Exception ( finally ) {- | Main database handle object. An 'IConnection' object is created by specific functions in the module for an individual database. That is, the connect function -- which creates this object -- is not standardized through the HDBC interface. A connection is closed by a call to 'disconnect'. A call to 'commit' is required to make sure that your changes get committed to the database. In other words, HDBC has /no support for autocommit/, which we consider an outdated notion. -} class IConnection conn where {- | Disconnect from the remote database. You do not need to explicitly close an IConnection object, but you may do so if you so desire. If you don't, the object will disconnect from the database in a sane way when it is garbage-collected. However, a disconnection may raise an error, so you are encouraged to explicitly call 'disconnect'. Also, garbage collection may not run when the program terminates, and some databases really like an explicit disconnect. So, bottom line is, you're best off calling 'disconnect' directly, but the world won't end if you forget. This function discards any data not committed already. Database driver implementators should explicitly call 'rollback' if their databases don't do this automatically on disconnect. Bad Things (TM) could happen if you call this while you have 'Statement's active. In more precise language, the results in such situations are undefined and vary by database. So don't do it. -} disconnect :: conn -> IO () {- | Commit any pending data to the database. Required to make any changes take effect. -} commit :: conn -> IO () {- | Roll back to the state the database was in prior to the last 'commit' or 'rollback'. -} rollback :: conn -> IO () {- | Execute an SQL string, which may contain multiple queries. This is intended for situations where you need to run DML or DDL queries and aren't interested in results. -} runRaw :: conn -> String -> IO () runRaw conn sql = do sth <- prepare conn sql _ <- execute sth [] `finally` finish sth return () {- | Execute a single SQL query. Returns the number of rows modified (see 'execute' for details). The second parameter is a list of replacement values, if any. -} run :: conn -> String -> [SqlValue] -> IO Integer {- | Prepares a statement for execution. Question marks in the statement will be replaced by positional parameters in a later call to 'execute'. Please note that, depending on the database and the driver, errors in your SQL may be raised either here or by 'execute'. Make sure you handle exceptions both places if necessary. -} prepare :: conn -> String -> IO Statement {- | Create a new 'Connection' object, pointed at the same server as this object is. This will generally establish a separate physical connection. When you wish to establish multiple connections to a single server, the correct way to do so is to establish the first connection with the driver-specific connection function, and then clone it for each additional connection. This can be important when a database doesn't provide much thread support itself, and the HDBC driver module must serialize access to a particular database. This can also be a handy utility function whenever you need a separate connection to whatever database you are connected to already. -} clone :: conn -> IO conn {- | The name of the HDBC driver module for this connection. Ideally would be the same as the database name portion of the Cabal package name. For instance, \"sqlite3\" or \"odbc\". This is the layer that is bound most tightly to HDBC. -} hdbcDriverName :: conn -> String {- | The version of the C (or whatever) client library that the HDBC driver module is bound to. The meaning of this is driver-specific. For an ODBC or similar proxying driver, this should be the version of the ODBC library, not the eventual DB client driver. -} hdbcClientVer :: conn -> String {- | In the case of a system such as ODBC, the name of the database client\/server in use, if available. For others, identical to 'hdbcDriverName'. -} proxiedClientName :: conn -> String {- | In the case of a system such as ODBC, the version of the database client in use, if available. For others, identical to 'hdbcClientVer'. This is the next layer out past the HDBC driver. -} proxiedClientVer :: conn -> String {- | The version of the database server, if available. -} dbServerVer :: conn -> String {- | Whether or not the current database supports transactions. If False, then 'commit' and 'rollback' should be expected to raise errors. MySQL is the only commonly-used database that is known to not support transactions entirely. Please see the MySQL notes in the ODBC driver for more information. -} dbTransactionSupport :: conn -> Bool {- | The names of all tables accessible by the current connection, excluding special meta-tables (system tables). You should expect this to be returned in the same manner as a result from 'Database.HDBC.fetchAllRows''. All results should be converted to lowercase for you before you see them. -} getTables :: conn -> IO [String] {- | Obtain information about the columns in a specific table. The String in the result set is the column name. You should expect this to be returned in the same manner as a result from 'Database.HDBC.fetchAllRows''. All results should be converted to lowercase for you before you see them. -} describeTable :: conn -> String -> IO [(String, SqlColDesc)] {- | Sometimes, it is annoying to use typeclasses with Haskell's type system. In those situations, you can use a ConnWrapper. You can create one with: >let wrapped = ConnWrapper iconn You can then use this directly, since a ConnWrapper is also an 'IConnection'. However, you will not be able to use private database functions on it. Or, you can use 'withWConn'. -} data ConnWrapper = forall conn. IConnection conn => ConnWrapper conn {- | Unwrap a 'ConnWrapper' and pass the embedded 'IConnection' to a function. Example: >withWConn wrapped run $ "SELECT * from foo where bar = 1" [] -} withWConn :: forall b. ConnWrapper -> (forall conn. IConnection conn => conn -> b) -> b withWConn conn f = case conn of ConnWrapper x -> f x instance IConnection ConnWrapper where disconnect w = withWConn w disconnect commit w = withWConn w commit rollback w = withWConn w rollback run w = withWConn w run prepare w = withWConn w prepare clone w = withWConn w (\dbh -> clone dbh >>= return . ConnWrapper) hdbcDriverName w = withWConn w hdbcDriverName hdbcClientVer w = withWConn w hdbcClientVer proxiedClientName w = withWConn w proxiedClientName proxiedClientVer w = withWConn w proxiedClientVer dbServerVer w = withWConn w dbServerVer dbTransactionSupport w = withWConn w dbTransactionSupport getTables w = withWConn w getTables describeTable w = withWConn w describeTable