user_guide_src/source/database/transactions.rst
############ Transactions ############
CodeIgniter's database abstraction allows you to use transactions with databases that support transaction-safe table types. In MySQL, you'll need to be running InnoDB or BDB table types rather than the more common MyISAM. Most other database platforms support transactions natively.
If you are not familiar with transactions we recommend you find a good online resource to learn about them for your particular database. The information below assumes you have a basic understanding of transactions.
.. contents:: :local: :depth: 3
CodeIgniter utilizes an approach to transactions that is very similar to the process used by the popular database class ADODB. We've chosen that approach because it greatly simplifies the process of running transactions. In most cases, all that is required is two lines of code.
Traditionally, transactions have required a fair amount of work to implement since they demand that you keep track of your queries and determine whether to commit or rollback based on the success or failure of your queries. This is particularly cumbersome with nested queries. In contrast, we've implemented a smart transaction system that does all this for you automatically (you can also manage your transactions manually if you choose to, but there's really no benefit).
.. note::
Since v4.3.0, during transactions, exceptions are not thrown by default
even if DBDebug is true.
To run your queries using transactions you will use the
$this->db->transStart() and $this->db->transComplete() methods as
follows:
.. literalinclude:: transactions/001.php
You can run as many queries as you want between the transStart()/transComplete()
methods and they will all be committed or rolled back based on the success
or failure of any given query.
By default, CodeIgniter runs all transactions in Strict Mode.
When strict mode is enabled, if you are running multiple groups of transactions, if one group fails all subsequent groups will be rolled back.
If strict mode is disabled, each group is treated independently, meaning a failure of one group will not affect any others.
Strict Mode can be disabled as follows:
.. literalinclude:: transactions/002.php
.. _transactions-resetting-transaction-status:
.. versionadded:: 4.6.0
When strict mode is enabled, if one transaction fails, all subsequent transactions will be rolled back.
If you wan to restart transactions after a failure, you can reset the transaction status:
.. literalinclude:: transactions/009.php
.. _transactions-managing-errors:
.. note::
Since v4.3.0, during transactions, exceptions are not thrown by default
even if DBDebug is true.
You can manage your own errors like this:
.. literalinclude:: transactions/003.php
.. _transactions-throwing-exceptions:
.. versionadded:: 4.3.0
.. note::
Since v4.3.0, during transactions, exceptions are not thrown by default
even if DBDebug is true.
If you want an exception to be thrown when a query error occurs, you can use
$this->db->transException(true):
.. literalinclude:: transactions/008.php
If a query error occurs, all the queries will be rolled backed, and a
DatabaseException will be thrown.
Transactions are enabled by default. If you would like to disable transactions you
can do so using $this->db->transOff():
.. literalinclude:: transactions/004.php
When transactions are disabled, your queries will be auto-committed, just as they are when running queries without transactions.
You can optionally put the transaction system into "test mode", which
will cause your queries to be rolled back -- even if the queries produce
a valid result. To use test mode simply set the first parameter in the
$this->db->transStart() method to true:
.. literalinclude:: transactions/005.php
.. _transactions-manual-transactions:
When you have DBDebug false in your app/Config/Database.php file, and
if you would like to run transactions manually you can do so as follows:
.. literalinclude:: transactions/006.php
.. note:: Make sure to use $this->db->transBegin() when running manual
transactions, NOT $this->db->transStart().
In CodeIgniter, transactions can be nested in a way such that only the
outmost or top-level transaction commands are executed. You can include as
many pairs of transStart()/transComplete() or transBegin()/transCommit()/transRollback()
as you want inside a transaction block and so on. CodeIgniter will keep
track of the transaction "depth" and only take action at the outermost layer
(zero depth).
.. literalinclude:: transactions/007.php
.. note:: In case the structure is far more complex, it's your responsibility to ensure that the inner transactions can reach the outermost layer again in order to be fully executed by the database, thus prevents unintended commits/rollbacks.