Copyright | Copyright (c) 2009-2010 Chris Waterson |
---|---|
License | LGPL |
Maintainer | bos@serpentine.com |
Stability | experimental |
Portability | GHC |
Safe Haskell | None |
Language | Haskell2010 |
This module provides a MySQL driver for the HDBC database interface.
To use it, invoke the connectMySQL
method to create an
Database.HDBC.IConnection
that you can use to interact with a MySQL
database. Use the defaultMySQLConnectInfo
, overriding the default
values as necessary.
import Control.Monad import Database.HDBC import Database.HDBC.MySQL main = do rows <-withRTSSignalsBlocked
$ do conn <-connectMySQL
defaultMySQLConnectInfo
{mysqlHost
= "db1.example.com",mysqlUser
= "scott",mysqlPassword
= "tiger" }quickQuery'
conn "SELECT 1 + 1" [] forM_ rows $ \row -> putStrLn $ show row
There are some important caveats to note about this driver.
- RTS signals. If you are writing an application that links against GHC's
threaded runtime (as most server-side applications do), you must use
withRTSSignalsBlocked
to defend themysqlclient
library against the signals the RTS uses, or you may experience crashes. - Transaction support. The MySQL server supports a variety of backend "engines", only some of which support transactional access (e.g., InnoDB). This driver will report that the database supports transactions. Should you decide to make use of the transactional support in the HDBC API, it is up to you to make sure that you use a MySQL engine that supports transactions.
- Dates and times. MySQL does not store time zone
information in
DATETIME
orTIMESTAMP
columns: instead, it assumes that all dates are stored in the "server's time zone". At some point in the future, this driver may query for the server's time zone and apply appropriate time zone conversion to these datatypes. For now, it simply treats all times as UTC; i.e., it assumes the server's time zone is UTC.
- data MySQLConnectInfo = MySQLConnectInfo {}
- data Connection
- connectMySQL :: MySQLConnectInfo -> IO Connection
- defaultMySQLConnectInfo :: MySQLConnectInfo
- withRTSSignalsBlocked :: IO a -> IO a
Documentation
data MySQLConnectInfo Source #
Connection information to use with connectMySQL.
You must either supply a host and port, or the full path to a Unix socket.
MySQLConnectInfo | |
|
connectMySQL :: MySQLConnectInfo -> IO Connection Source #
Connects to a MySQL database using the specified connection information.
defaultMySQLConnectInfo :: MySQLConnectInfo Source #
Typical connection information, meant to be overridden partially, for example:
connectMySQL defaultMySQLConnectInfo { mysqlHost = "db1" }
In particular, the default values are "127.0.0.1"
as the
host, 3306
as the port, "root"
as the user, no password,
and "test"
as the default database.
withRTSSignalsBlocked :: IO a -> IO a Source #
Execute an IO
action with signals used by GHC's runtime signals
blocked. The mysqlclient
C library does not correctly restart
system calls if they are interrupted by signals, so many MySQL API
calls can unexpectedly fail when called from a Haskell application.
This is most likely to occur if you are linking against GHC's
threaded runtime (using the -threaded
option).
This function blocks SIGALRM
and SIGVTALRM
, runs your action,
then unblocks those signals. If you have a series of HDBC calls
that may block for a period of time, it may be wise to wrap them in
this action. Blocking and unblocking signals is cheap, but not
free.
Here is an example of an exception that could be avoided by temporarily blocking GHC's runtime signals:
SqlError { seState = "", seNativeError = 2003, seErrorMsg = "Can't connect to MySQL server on 'localhost' (4)" }