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« 2. Installation

3. Make your Symfony2 bundle extendable

Note

This post is not part of the Symfony2 documentation; it is just a state about how things work now (end of 2010) between Doctrine2 and Symfony2. It is not a complaint about the architecture, it just exposes how I solve a recurrent problem I have.

3.1. Let’s have a quick Symfony2 and Doctrine tour

A quick Doctrine tour:

  • Doctrine2 entities are plain PHP objects; there is no database layer information. An Comment::post_id property is part of the database layer and not part of the domain layer. So a comment entity will have a post property and not a post_id property.
  • Doctrine2 entities are mapped through mapping information: yaml, xml, annotation or php code. There is one mapping per class, so if Blog extends SuperBlog, which extends SuperEntity, you will have 3 classes and so 3 information mappings and you will be able to use 3 different tables to save these entities,
  • A mapped entity is final (from Doctrine2 point of view), it cannot be extended unless you create a new mapping definition for the new child class,
  • Each entity is linked to a ClassMetadata information which contains all the mapping information and the final class name,
  • An entity can extend a SuperClass. A SuperClass is just a mapping definition, a SuperClass cannot be persisted.

A quick Symfony2 bundle tour:

  • There are two types of bundles:

    • Application Bundle (AB),
    • Vendor Bundle (VB), that should not be modified inside a project.
  • The AB directory is where developers implement the project requirements,

  • An AB can overwrite almost everything from a VB, example: you can redefine a VB template at the AB level.

A namespace tour:

  • “a namespace is an abstract container providing context for the items” (Source),
  • An entity is defined by a namespace,
  • A bundle is defined by a namespace,
  • A VB and AB are defined with two different namespaces.

3.2. Let’s start to mix these points together

  • If an AB bundle A wants to use an entity from a VB bundle B, the fully qualify namespace must be used,
  • If a developer wants to add a new property into a VB entity, the developer needs to create a new child entity with a custom mapping.

At this point, you have 2 entities with 2 different namespaces. The VB bundle’s code refers to its own namespace to instantiate the model, BUT … how … you just create a new entity. Your VB will be unable to use this new model … too bad.

3.3. Can this problem be solved with the Alternate syntax?

There is actually a start of a solution, the DoctrineBundle allows us to use an alternate syntax, ie (BlogBundle:Blog instead of Bundle\BlogBundle\Entity\Blog). As you can guess this syntax only works for string, inside a query for instance.

So if you want to instantiate a new model, you need first to get the ClassMetadata instance, retrieve the class name and create the model. It’s not really nice and creates a dependency to the class metadata.

Last issue, the entity’s mapping association required fully qualifies namespace: no alternate syntax. (I suppose, this last point can be fixed).

At this point, we are stuck with no solution to fully extend a bundle. (Don’t take this for granted; this might change in a near future, as Symfony2 is not complete yet)

3.4. A pragmatic way to solve this issue

The easiest way to solve this problem is to use global namespace inside your VB, the global namespace is the only namespace allowed Application\YourBundle\Entity.

So, inside your mapping definition or inside your VB code, you will use one final namespace: problem solved. How to achieve this:

  • Declare only SuperClass inside a VB, don’t use final entity,
  • Call your entity BaseXXXX and make it abstract, change the properties from private to protected,
  • The same goes for a repository,
  • Always use Application\YourBundle\Entity\XXXX inside your code.

Of course, you need to create for each VB bundle:

  • a valid structure inside the Application directory,
  • a valid entity mapping definition,
  • a model inside the entity folder.

The last part is quite inefficient without an efficient tool to generate for you this structure: EasyExtendsBundle to the rescue.

3.5. How to make your bundle easy extendable?

Mainly all you need is to follow instructions in previous paragraph:

  • Declare you entity/repository as described above,
  • Use your entity/repository as described above,
  • Before generation you also need “skeleton” file that will describe AB entity. Skeleton file can either xml or yml. For fully working example see SonataMediaBundle.

At last you can run:

bin/console sonata:easy-extends:generate YourVBBundleName

3.6. Command Options

There are few options that you can add when executing command:

  • the --dest option allows you to choose the target directory, such as src. The default destination is the directory of your Kernel.
  • the --namespace option allows you to choose the base namespace, such as Application\Sonata. The default destination is Application\:vendor.
  • the --namespace_prefix option allows to provide a prefix for your namespace, this option is added because of the new directory structure that symfony-flex brings us. There is no Default value so if you are using flex you should use this option with the App value.

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