db\Transaction begin()

The isolation level to use for this transaction. This can be one of READ_UNCOMMITTED, READ_COMMITTED, REPEATABLE_READ and SERIALIZABLE but also a string containing DBMS specific syntax to be used after SET TRANSACTION ISOLATION LEVEL. If not specified (null) the isolation level will not be set explicitly and the DBMS default will be used.

Note: This setting does not work for PostgreSQL, where setting the isolation level before the transaction has no effect. You have to call setIsolationLevel() in this case after the transaction has started.

Note: Some DBMS allow setting of the isolation level only for the whole connection so subsequent transactions may get the same isolation level even if you did not specify any. When using this feature you may need to set the isolation level for all transactions explicitly to avoid conflicting settings. At the time of this writing affected DBMS are MSSQL and SQLite.

if $db is null.