Month: February 2022

Why transactions are a good thing.

Let’s say that in your application all users have to belong to a team. And in your createUser action, you create a user and then you assign this user a team.

$user = User::create(['email'=> '[email protected]');

$user->teams()->attach($team->id); //Throws an exception

If you get an Exception while attaching the Team to the User, your application ends with a wrong state where you have a User which hasn’t a Team assigned.

This is simple to fix in this case, but it can be more complex in other cases and by using database transactions will yourself these state fixes. Because, when using database transactions, if the team assignment throws an exception, your application will also prevent the user creation.

How to implement write transactions in Laravel

Database transactions are good practice for all write actions. Therefore we create a global middleware for this, using the following command.

$ php artisan make:middleware DatabaseTransaction

and we change the handle method like below:

//app/Http/Middleware/DatabaseTransaction.php

public function handle($request, \Closure $next)
{
		if (!in_array($request->method(),['POST','PUT','PATCH','DELETE'])) {
			return $next($request);
		}

		DB::beginTransaction();

    try {
        $response = $next($request);
    } catch (\Exception $e) {

        DB::rollBack();

        throw $e;
    }
	
    if ($response->getStatusCode() > 399) {
        DB::rollBack();
    } else {
        DB::commit();
    }

    return $response;
}

This code will check if we make a write operation by checking if the request method of the request is a write one, and start a transaction. If within the write request something goes wrong it will roll back the transaction.

The only thing left to do is to register the middleware to our web middleware group in the app/Http/Kernel.php.

//app/Http/Kernel.php

protected $middlewareGroups = [
    'web' => [
			// ...
			\App\Http\Middleware\DatabaseTransaction::class
    ],
];

Now your application will use this DatabaseTransaction middleware on every request.

What to keep in mind

Once you have fully integrated database transactions in your applications, there is this one thing that you need to watch out for when dispatching jobs. If you dispatch a job and later your application rolls back, your job will still be processed by your queue.

For that reason, Laravel has the afterCommit method which you can chain after the dispatch. This way you are safe that the dispatch will only run if the response was successful.

So if you also are sending an email after the user creation, your code should look like this:

$user = User::create(['email'=> '[email protected]');

$user->teams()->attach($team->id);

dispatch(new SendWelcomeEmail($user))->afterCommit();

Final words

The accuracy, completeness, and reliability of your database data are viable things for your application. Using database transactions in Laravel is easy for us to take advantage of them.