事务
CodeIgniter的数据库抽象允许你在支持事务安全的数据库表中使用事务在MySQL中，你需要用InnoDB或BDB表而不是更常用的MyISAM。Most other database platforms support transactions natively.
如果你对事务不熟悉，我们建议您上网寻找相关资源学习。以下信息假设你已经明白事务的相关概念。
CodeIgniter's Approach to Transactions
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 are two lines of code.
Traditionally, transactions have required a fair amount of work to implement since they demand that you to 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).
Running Transactions
To run your queries using transactions you will use the $this->db->trans_start() and $this->db->trans_complete() functions as follows:
$this->db->trans_start();
$this->db->query('AN SQL QUERY...');
$this->db->query('ANOTHER QUERY...');
$this->db->query('AND YET ANOTHER QUERY...');
$this->db->trans_complete();
You can run as many queries as you want between the start/complete functions and they will all be committed or rolled back based on success or failure of any given query.
Strict Mode
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 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:
$this->db->trans_strict(FALSE);
Managing Errors
If you have error reporting enabled in your config/database.php file you'll see a standard error message if the commit was unsuccessful. If debugging is turned off, you can manage your own errors like this:
$this->db->trans_start();
$this->db->query('AN SQL QUERY...');
$this->db->query('ANOTHER QUERY...');
$this->db->trans_complete();
if ($this->db->trans_status() === FALSE)
{
// generate an error... or use the log_message() function to log your error
}
Enabling Transactions
Transactions are enabled automatically the moment you use $this->db->trans_start(). If you would like to disable transactions you can do so using $this->db->trans_off():
$this->db->trans_off()
$this->db->trans_start();
$this->db->query('AN SQL QUERY...');
$this->db->trans_complete();
When transactions are disabled, your queries will be auto-commited, just as they are when running queries without transactions.
Test Mode
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->trans_start() function to TRUE:
$this->db->trans_start(TRUE); // Query will be rolled back
$this->db->query('AN SQL QUERY...');
$this->db->trans_complete();
Running Transactions Manually
If you would like to run transactions manually you can do so as follows:
$this->db->trans_begin();
$this->db->query('AN SQL QUERY...');
$this->db->query('ANOTHER QUERY...');
$this->db->query('AND YET ANOTHER QUERY...');
if ($this->db->trans_status() === FALSE)
{
$this->db->trans_rollback();
}
else
{
$this->db->trans_commit();
}
Note: Make sure to use $this->db->trans_begin() when running manual transactions, NOT $this->db->trans_start().
