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Config

When Symfony loads, it needs to figure out all of the services that should be in the container.

Look at config/services.yaml:

services:
    # default configuration for services in *this* file
    _defaults:
        autowire: true      # Automatically injects dependencies in your services.
        autoconfigure: true # Automatically registers your services as commands, event subscribers, etc.
        public: false
        
    App\Service\MarkdownService:
        autowire: false

This is a special key _defaults sets default config values that should be applied to all services that are registered in this file.

We could set autowiring to false on just one service to override these defaults.

Service auto-registration

Look at config/services.yaml:

services:
    # makes classes in src/ available to be used as services
    # this creates a service per class whose id is the fully-qualified class name
    App\:
        resource: '../src/*'
        exclude: '../src/{Entity,Migrations,Tests}'

This makes all classes inside src/ available as services in the container.

Remember: each class in the src/ directory is automatically registered as a service

But wait! Does that mean that all of our classes are instantiated on every single request? No: this line simply tells the container to be aware of these classes. But services are never instantiated until - and unless - someone asks for them. So, if we didn't ask for our MarkdownService, it would never be instantiated on that request.

Important: each service in the container is instantiated a maximum of once per request. If multiple parts of our code ask for the MarkdownHelper, it will be created just once, and the same instance will be passed each time. That's awesome for performance: we don't need multiple markdown helpers... even if we need to call parse() multiple times.

Bind service to variable name

Edit config/services.yaml:

services:
    # default configuration for services in *this* file
    _defaults:
        bind:
            $markdownLogger: '@monolog.logger.markdown'

This config tells: if you find any argument named $markdownLogger, pass this service to it. And because we added it to _defaults, it applies to all our services. Instead of configuring our services one-by-one, we're creating project-wide conventions. Next time you need this logger? Yep, just name it $markdownLogger and keep coding.

Bind class name to service

Edit config/services.yaml:

services:
    Nexy\Slack\Client: '@nexy_slack.client'

It allows us to autowire class Nexy\Slack\Client.

By putting this config directly under services, we're creating a new service in the container with the id Nexy\Slack\Client. But this is not a real service, it's just an "alias" - a "shortcut" - to fetch the existing nexy_slack.client service.

Important: when an argument to a service hasn't been configured under bind or arguments, how does the autowiring figure out which service to pass? The answer is super simple: it just looks for a service whose id exactly matches the type-hint. Yep, now that there is a service whose id is Nexy\Slack\Client, we can use that class as a type-hint. That's also why our classes - like MarkdownHelper can be autowired: each class in src/ is auto-registered as a service and given an id that matches the class name.

Parameters

Edit common config file config/services.yaml:

parameters:
    cache_adapter: cache.adapter.apcu

For development environment we create config/services_dev.yaml:

parameters:
    cache_adapter: cache.adapter.filesystem

After that we can use this cache_adapter param in config/packages/framework.yaml:

framework:
    cache:
        app: '%cache_adapter%'

Remember: anything surrounded by percent signs is a parameter (eg. cache_adapter%)

kerner.secret

If you ever need a cryptographic secret, Symfony has a parameter called kernel.secret. We can use %kernel.secret% to get it in yaml config files.

Envirinment variables

Set variable

Edit .env:

### CUSTOM VARS
SLACK_WEBHOOK_ENDPOINT=https://hooks.slack.com/services/26/B91D3PPH/BX20IHE2
### END CUSTOM VARS

To save the name of this variable to version control edit .env.dist:

### CUSTOM VARS
SLACK_WEBHOOK_ENDPOINT=https://hooks.slack.com/services/...
### END CUSTOM VARS

Important: Using .env isn't recommended for production is mostly because the logic to parse this file isn't optimized. So, you'll lose a small amount of performance - probably just a couple of milliseconds.

Read variable

Edit config/packages/nexy_slack.yaml:

nexy_slack:
    endpoint: '%env(SLACK_WEBHOOK_ENDPOINT)%'

Note: Use this syntax to get environment var in yaml config: %env(APP_SECRET)%

Cast variables

You can cast values by prefixing the name with, for example, string:, bool:, float::

nexy_slack:
    endpoint: '%env(string:SLACK_WEBHOOK_ENDPOINT)%'
    is_verbose: '%env(bool:SLACK_IS_VERBOSE)%'

Chain prefixes

We can open a file, and then decode its JSON:

app.secrets: '%env(json:file:SECRETS_FILE)%'

Bundle config

Each file in config/packages/ configures a some bundle. Any configuration under knp_markdown is passed to the KnpMarkdownBundle. Any config under framework configures FrameworkBundle, which is Symfony's one, "core" bundle.

Show default bundle config

./bin/console config:dump TwigBundle

Also we can use alias:

./bin/console config:dump knp_markdown