@Martin-P i think string should be already fine, see here: https://github.com/zendframework/zf2/blob/master/library/Zend/Log/Logger.php#L236-L250

But i think you have to use the FQN: Zend\Log\Writer\Db

Does that work?

But i think you have to use the FQN: Zend\Log\Writer\Db

Thanks for your reply, but the location of the writer is not the problem. The writer is found and the exception (see opening post) is thrown by the correct writer. If the writer itself could not be found, it would not be able to throw an exception.

The problem is the database adapter. Zend\Log\Writer\Db says the adapter is not valid, because it only accepts an instance of Zend\Db\Adapter\Adapter.

Because you want to be able to cache your config, it should be possible to get a database adapter by providing a string. The constructor of Zend\Log\Writer\Db should detect that the db parameter is a string and try to get an instance of the adapter via the service manager.

Ah sorry 😄 ....the same problem, but one "array level" deeper =)

The problem is that the LoggerAbstractServiceFactory simply passes the configuration on to the Logger's constructor -- and the Logger class does not have access to the service manager.

The solution would be to pre-analyze the configuration to see if it contains any DB writers, and, if so, pull the associated adapter and replace the configuration value with that adapter. I'll see if I can work something up.

This fix introduces a new problem. It is now impossible to extend the Zend\Log\Writer\Db and use my own writer in the config like this:

'log' => array(
    'Application\Log' => array(
        'writers' => array(
            array(
                'name'     => 'MyLog\Writer\DbWriter',
                'priority' => 1,
                'options'  => array(
                    'separator' => '_',
                    'column'    => array(),
                    'table'     => 'applicationlog',
                    'db'        => 'Zend\Db\Adapter\Adapter',
                ),
            ),
        ),
    ),
),

I need my own writer to compensate for a bug #2589 that still exist in Zend\Log\Writer\Db. The check on line 99 of Zend/Log/LoggerAbstractServiceFactory is the cause of this problem:

|| strtolower($writerConfig['name']) != 'db'

That check is not needed at all and makes it impossible to use my own writer. The checks on the following lines already check if $writerConfig['options']['db'] exist and that is enough. If for some reason there is an invalid writer provided in the config, Zend\Log\WriterPluginManager throws an exception and therefore all possible scenarios are already covered by the existing code.

Edit:
Nevermind this post, I thought fixing this bug would make Zend\Logger usable via config, but it still has too many issues.

@Martin-P I was testing on the writer name, but really I only need to test for a "db" option. I'll create a PR for that in the next day or two.

A bit late, but thanks, #5588 fixed the issue with the custom writer.