All about the Bundle Extension Config System

We're not passing any arguments to the service... but this class does have two very important arguments: whether or not unicorns are real and the minimum times the word sunshine should appear in each paragraph. But what if a user of our bundle wants more sunshine or - gasp - they don't believe in unicorns? Right now, there's no way for them to control these arguments.

So if the bundle is responsible for registering the services & passing its arguments, how can the user of that bundle control those arguments? The answer lives in the config/packages directory.

Some important notes: first, our app automatically loads & processes all .yaml files it finds in this directory. Second, the names of these files are not important: you could rename them to anything else, .yaml. And third, the entire purpose of these files is to control the services that are provided by different bundles. When Symfony sees the framework key, it passes this configuration to the FrameworkBundle, which uses it to modify the services it provides.

The same for monolog: this config is passed to MonologBundle and it uses that when registering its services.

Creating a New Config File

Create a new file: knpu_lorem_ipsum.yaml - but, we could call this anything. And just to see what will happen, add some fake config: foo:, then bar: true.

Find your browser and refresh! Error! Check out the language carefully. It says that there is no extension able to load the configuration for "foo". We know that word extension: we just created our own extension: KnpULoremIpsumExtension.

Then, since foo is apparently invalid, it lists a bunch of valid keys, like framework, web_server, twig, etc. Here's the deal: when Symfony sees a root key like framework, it looks at all of the bundles, well, really, the extension class for each bundle, to see if there is one called FrameworkExtension. If there is, it passes the config to it. If there is not, it throws this big, hairy, ugly exception.

Passing Config to our Extension

But check this out: go back to the list of valid keys. Thanks to our KnpULoremIpsumExtension class, there's one called knp_u_lorem_ipsum! Change the root key to use that instead.

Next, open our extension class, var_dump($configs) and die.

Try it out! No error! And cool! That bar: true value is passed to the load method! We're one step closer to using that config to tweak our service.

But, there are two weird things. First, the root key is... uh... not perfect. The knp_u_ is.. weird - I want it be knpu_... but apparently Symfony disagrees: our extra capital "U" is confusing things. We'll fix this in a bit.

The second weird thing is that the $configs value that's passed to load() is not just a simple array with bar=true. Nope, it's an array of arrays. Inception. Why? Well, it's possible that the user could add configuration for our bundle in multiple files. Like, we could have a dev environment-specific YAML file. When that happens, instead of merging that config together, it would pass us the configuration from both files. For example, if knp_u_lorem_ipsum existed in three different files, this array would have three different arrays inside. And, yep! It will be our job to merge them together. But, that's actually going to be really cool.

But before we do that, let's fix our alias to be knpu_lorem_ipsum. It's not something you often need to worry about, but the fix is super interesting.