This optional parameter specifies a Hook that is run every time this clause connects or reconnects to the SQL database. This is most useful for executing func() to configure the database connection in customised ways. The hook is called with 2 arguments. The first is a reference to the clause object that is making the connection. The second argument is the DBH handle to the newly connected database.

In the following example, the hook calls DBI func() to configure an Interbase database connection for custom requirements:

ConnectionHook sub {$_[1]->func(-access_mode => 'read_write',\
      -isolation_level => 'read_committed',\
      -lock_resolution => 'wait',\
      'ib_set_tx_param')}