1PHP Data Objects 2================ 3 4Concept: Data Access Abstraction 5 6Goals: 7 81/ Be light-weight 92/ Provide common API for common database operations 103/ Be performant 114/ Keep majority of PHP specific stuff in the PDO core (such as persistent 12 resource management); drivers should only have to worry about getting the 13 data and not about PHP internals. 14 15 16Transactions and autocommit 17=========================== 18 19When you create a database handle, you *should* specify the autocommit 20behaviour that you require. PDO will default to autocommit on. 21 22$dbh = new PDO("...", $user, $pass, array(PDO_ATTR_AUTOCOMMIT => true)); 23 24When auto-commit is on, the driver will implicitly commit each query as it is 25executed. This works fine for most simple tasks but can be significantly 26slower when you are making a large number of udpates. 27 28$dbh = new PDO("...", $user, $pass, array(PDO_ATTR_AUTOCOMMIT => false)); 29 30When auto-commit is off, you must then use $dbh->beginTransaction() to 31initiate a transaction. When your work is done, you then call $dbh->commit() 32or $dbh->rollBack() to persist or abort your changes respectively. Not all 33databases support transactions. 34 35You can change the auto-commit mode at run-time: 36 37$dbh->setAttribute(PDO_ATTR_AUTOCOMMIT, false); 38 39Regardless of the error handling mode set on the database handle, if the 40autocommit mode cannot be changed, an exception will be thrown. 41 42Some drivers will allow you to temporarily disable autocommit if you call 43$dbh->beginTransaction(). When you commit() or rollBack() such a transaction, 44the handle will switch back to autocommit mode again. If the mode could not 45be changed, an exception will be raised, as noted above. 46 47When the database handle is closed or destroyed (or at request end for 48persistent handles), the driver will implicitly rollBack(). It is your 49responsibility to call commit() when you are done making changes and 50autocommit is turned off. 51 52vim:tw=78:et 53
