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55 lines
1.9 KiB
Plaintext
Executable File
55 lines
1.9 KiB
Plaintext
Executable File
PHP Data Objects
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Concept: Data Access Abstraction
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Goals:
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1/ Be light-weight
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2/ Provide common API for common database operations
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3/ Be performant
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4/ Keep majority of PHP specific stuff in the PDO core (such as persistent
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resource management); drivers should only have to worry about getting the
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data and not about PHP internals.
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Transactions and autocommit
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===========================
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When you create a database handle, you *should* specify the autocommit
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behaviour that you require. PDO will default to autocommit on.
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$dbh = new PDO("...", $user, $pass, array(PDO_ATTR_AUTOCOMMIT => true));
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When auto-commit is on, the driver will implicitly commit each query as it is
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executed. This works fine for most simple tasks but can be significantly
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slower when you are making a large number of udpates.
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$dbh = new PDO("...", $user, $pass, array(PDO_ATTR_AUTOCOMMIT => false));
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When auto-commit is off, you must then use $dbh->beginTransaction() to
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initiate a transaction. When your work is done, you then call $dbh->commit()
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or $dbh->rollBack() to persist or abort your changes respectively. Not all
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databases support transactions.
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You can change the auto-commit mode at run-time:
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$dbh->setAttribute(PDO_ATTR_AUTOCOMMIT, false);
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Regardless of the error handling mode set on the database handle, if the
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autocommit mode cannot be changed, an exception will be thrown.
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Some drivers will allow you to temporarily disable autocommit if you call
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$dbh->beginTransaction(). When you commit() or rollBack() such a transaction,
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the handle will switch back to autocommit mode again. If the mode could not
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be changed, an exception will be raised, as noted above.
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When the database handle is closed or destroyed (or at request end for
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persistent handles), the driver will implicitly rollBack(). It is your
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responsibility to call commit() when you are done making changes and
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autocommit is turned off.
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vim:tw=78:et
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