Service Container

Service Container

Introduction

The Service Container is an extremely powerful feature of Masonite and should be used to the fullest extent possible. It's important to understand the concepts of the Service Container. It's a simple concept but is a bit magical if you don't understand what's going on under the hood.

Getting Started

The Service Container is just a container where classes are loaded into it by key-value pairs, and then can be retrieved by either the key or value. That's it.

The container is contained inside the App class which is instantiated throughout in the beginning of the framework and passed through various parts of the project such as controllers, middleware and drivers.

We can create easily create service providers using a craft command:

$ craft provider DashboardProvider This will create a new service provider in app/providers/DashboardServiceProvider.py. Inside our new service provider we will have a register method and a boot method. It's important to know what each one does. We'll discuss both in a little bit.

Configuration

Once you create your service provider, you'll have to add it to your PROVIDERS list inside your config/application.py file. This should be a string to the location of the class:

PROVIDERS = [
    'app.providers.UserModelProvider.UserModelProvider'
    'app.providers.DashboardProvider.DashboardProvider'
]

Register

The register methods on all service providers are executed first, then all the boot methods are executed after. Because of this, the register method should only be used to load things into the container.

Boot

The boot method is executed on all service providers after the register methods on all service providers have been called. Because of this, the boot method will have access to everything inside the container and is resolved by Masonite's container.

Binding

In order to bind classes into the container, we will just need to use a simple bind method on our app container. In a service provider, that will look like:

from masonite.provider import ServiceProvider
from app.User import User
from masonite.request import Request

class UserModelProvider(ServiceProvider):

    def register(self):
        self.app.bind('User', User)

    def boot(self):
        pass

This will load the key value pair in the providers dictionary in the container. The dictionary after this call will look like:

>>> app.providers
{'User': User}

The service container is injected into the Request object and can be retrieved by:

def show(self, Request):
    Request.app() # will return the service container

Using the container

The container can be used in two ways: making and resolving.

Making

In order to retrieve a class from the service container, we can simply use the make method.

>>> from app.User import User
>>> app.bind('User', User)
>>> app.make('User')
<class app.User.User>

That's it! This is useful as an IOC container which you can load a single class into the container and use that class everywhere throughout your project.

Resolving

This is the most useful part of the container. It is possible to retrieve objects from the container by simply passing them into the parameters. Certain aspects of Masonite are resolved such as controller methods, middleware and drivers.

For example, we can hint that we want to get the Request class and put it into our controller. All controller methods are resolved by the container.

def show(self, Request)
    Request.user()

In this example, Masonite will look inside the container for a key called Request and return that value from the container. Request is already loaded into the container for you out of the box.

Another way to resolve classes is by using Python 3 annotations:

from masonite.request import Request

def show(self, request: Request)
    request.user()

Masonite will know that you are trying to get the Request class and will actually retrieve that class from the container. Masonite will search the container for a Request class regardless of what the key is in the container, retrieve it, and inject it into the controller method. Effectively creating an IOC container with dependency injection.

Pretty powerful stuff, eh?

Resolving your own code

The service container can also be used outside of the flow of Masonite. Masonite takes in a function or class method, and resolves it's dependencies by finding them in the service container and injecting them.

Because of this, you can resolve any of your own classes or functions.

from masonite.request import Request

def randomFunction(User):
    print(User)

def show(self, Request):
    Request.app().resolve(randomFunction) # Will print the User object

Remember not to call it and only reference the function. The Service Container needs to inject dependencies into the object so it requires a reference and not a callable.

This will fetch all of the parameters of randomFunction and retrieve them from the service container. There probably won't be many times you'll have to resolve your own code but the option is there.