About 2 years ago I created a package that combines the power of two famous Symfony components: the Form component and the Console component. In short: this package allows you to interactively fill in a form by typing in the answers at the CLI. When I started working on it, this seemed like a pretty far-fetched idea. However, it made a lot of sense to me in terms of a ports & adapters architecture that I was looking for back then (and still always am, by the way). We could (and often should) write the code in our application layer in such a way that it doesn’t make a big difference whether we call applications services from a web controller or from a CLI “controller”.

The Symfony Form Component has an architecture that keeps inspiring me. It supports horizontal and vertical inheritance and it has a solid event system on a very fine-grained level. In this post I would like to explain how you can expand the event system with your own events. As an example., I will create a new event type used for indicating that the bound form is valid.

Using event listeners and event subscribers with forms

As you can read in a Symfony Cookbook article you can already hook into special form events, defined in Symfony\Component\Form\FormEvents:

In my previous post I wrote about uploading files to GridFS. Therefor I created a MongoDB Document with a $file property annotated with @MongoDB\File. Because I am using ORM entities more often then ODM documents, I was looking for a seamless way to access a Document from an Entity.

Because it isn’t possible to define a direct relationship between an Entity and a Document I thought it would be a solid solution to create a custom field type. By defining a custom field type I can control the way the reference to the Document will be stored and at the same time I will be able to restore the reference when retrieving the field. The steps needed to create a custom field type for ORM entities are very similar to the post of Matthias on how to create custom field types for ODM documents.

With Symfony2, many things are managed through dependency injection. Except for forms. Oh, wait, forms can be services too of course! Remember? Any class instance can be a service… Now, as in many other cases, Symfony2’s FrameworkBundle adds some magic to the Form component by creating services that link several parts of the Form component together. For example, depending on the value of the framework.csrf_protection parameter in config.yml file a hidden field “_token” will be added to all forms, site-wide. To create this kind of very general “form extension” in your own project, you need to do just a few things (I am going to use the example of a “Captcha” form extension, but I don’t give a full implementation of this idea).