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Logging in Yii is really flexible. Basics are easy but sometimes it takes time to configure everything to get what you want. There are some ready to use solutions collected below. Hopefully you'll find what you're looking for.

Write 404 to file and send the rest via email

404 not found happens too often to email about it. Still, having 404s logged to a file could be useful. Let's implement it.

'components' => [
    'log' => [
        'targets' => [
            'file' => [
                'class' => 'yii\log\FileTarget',
                'categories' => ['yii\web\HttpException:404'],
                'levels' => ['error', 'warning'],
                'logFile' => '@runtime/logs/404.log',
            ],
            'email' => [
                'class' => 'yii\log\EmailTarget',
                'except' => ['yii\web\HttpException:404'],
                'levels' => ['error', 'warning'],
                'message' => ['from' => 'robot@example.com', 'to' => 'admin@example.com'],
            ],
        ],
    ],
],

When there's unhandled exception in the application Yii logs it additionally to displaying it to end user or showing customized error page. Exception message is what actually to be written and the fully qualified exception class name is the category we can use to filter messages when configuring targets. 404 can be triggered by throwing yii\web\NotFoundHttpException or automatically. In both cases exception class is the same and is inherited from \yii\web\HttpException which is a bit special in regards to logging. The speciality is the fact that HTTP status code prepended by : is appended to the end of the log message category. In the above we're using categories to include and except to exclude 404 log messages.

Immediate logging

By default Yii accumulates logs till the script is finished or till the number of logs accumulated is enough which is 1000 messages by default for both logger itself and log target. It could be that you want to log messages immediately. For example, when running an import job and checking logs to see the progress. In this case you need to change settings via application config file:

'components' => [
    'log' => [
        'flushInterval' => 1, // <-- here
        'targets' => [
            'file' => [
                'class' => 'yii\log\FileTarget',
                'levels' => ['error', 'warning'],
                'exportInterval' => 1, // <-- and here
            ],
        ],
    ]
]

Write different logs to different files

Usually a program has a lot of functions. Sometimes it is necessary to control these functions by logging. If everything is logged in one file this file becomes too big and too difficult to maintain. Good solution is to write different functions logs to different files.

For example you have two functions: catalog and basket. Let's write logs to catalog.log and basket.log respectively. In this case you need to establish categories for your log messages. Make a connection between them and log targets by changing application config file:

'components' => [
    'log' => [
        'targets' => [
                [
                    'class' => 'yii\log\FileTarget',
                    'categories' => ['catalog'],
                    'logFile' => '@app/runtime/logs/catalog.log',
                ],
                [
                    'class' => 'yii\log\FileTarget',
                    'categories' => ['basket'],
                    'logFile' => '@app/runtime/logs/basket.log',
                ],
        ],
    ]
]

After this you are able to write logs to separate files adding category name to log function as second parameter. Examples: 

\Yii::info('catalog info', 'catalog');
\Yii::error('basket error', 'basket');
\Yii::beginProfile('add to basket', 'basket');
\Yii::endProfile('add to basket', 'basket');

Disable logging of your own actions

Problem

You want to receive an email when a new user signs up, but you don't want to trace your own sign-up tests.

Solution

At first mark logging target inside config.php by key:

'log' => [
    // ...
    'targets' => [
            // email is a key for our target
            'email' => [  
                'class' => 'yii\log\EmailTarget',
                'levels' => ['info'],
                'message' => ['from' => 'robot@example.com', 'to' => 'admin@example.com'],
            ],
    // ...

Then, for example, inside Controller beforeAction you can create a condition:

    public function beforeAction($action)
    {
        // '127.0.0.1' - replace by your IP address
        if (in_array(@$_SERVER['REMOTE_ADDR'], ['127.0.0.1'])) {
            Yii::$app->log->targets['email']->enabled = false; // Here we disable our log target
        }
        return parent::beforeAction($action);
    }

Log everything but display different error messages

Problem

You want to log concrete server error but display only broad error explanation to the end user.

Solution

If you catch an error appropriate log target doesn't work. Let's say you have such log target configuration: 

'components' => [
    'log' => [
        'targets' => [
            'file' => [
                'class' => 'yii\log\FileTarget',
                'levels' => ['error', 'warning'],
                'logFile' => '@runtime/logs/error.log',
            ],
        ],
    ],
],

As an example let's add such code line inside actionIndex:

    public function actionIndex()
    {
        throw new ServerErrorHttpException('Hey! Coding problems!');
        // ...

Go to index page and you will see this message in the browser and in the error.log file.

Let's modify our actionIndex:

    public function actionIndex()
    {
        try {
            throw new ServerErrorHttpException('Hey! Coding problems!'); // here is our code line now
        }
        catch(ServerErrorHttpException $ex) {
            Yii::error($ex->getMessage()); // concrete message for us
            throw new ServerErrorHttpException('Server problem, sorry.'); // broad message for the end user
        }
    // ..

As the result in the browser you will see Server problem, sorry.. But in the error.log you will see both error messages. In our case second message is not necessary to log.

Let's add category for our log target and for logging command.

For config:

'file' => [
    'class' => 'yii\log\FileTarget',
    'levels' => ['error', 'warning'],
    'categories' => ['serverError'], // category is added
    'logFile' => '@runtime/logs/error.log',
],

For actionIndex:

catch(ServerErrorHttpException $ex) {
    Yii::error($ex->getMessage(), 'serverError'); // category is added
    throw new ServerErrorHttpException('Server problem, sorry.');
}

As the result in the error.log you will see only the error related to Hey! Coding problems!.

Even more

If there is an bad request (user side) error you may want to display error message 'as is'. You can easily do it because our catch block works only for ServerErrorHttpException error types. So you are able to throw something like this:

throw new BadRequestHttpException('Email address you provide is invalid');

As the result end user will see the message 'as is' in his browser.

See also