Dependency Container and Injection
In this document, you’ll learn what the dependency container is and how you can use it in Medusa with dependency injection.
Introduction
What is Dependency Injection
Dependency Injection is the act of delivering the required resources to a class. These resources are the class’s dependencies. This is usually done by passing (or injecting) the dependencies in the constructor of the class.
Generally, all resources are registered in a container. Then, whenever a class depends on one of these resources, the system retrieves the resources from the container and injects them into the class’s constructor.
Medusa’s Dependency Container
Medusa uses a dependency container to register essential resources of the backend. You can then access these resources in classes and API Routes using the dependency container.
For example, if you create a custom service, you can access any other service registered in Medusa in your service’s constructor. That includes Medusa’s core services, services defined in plugins, or other services that you create on your backend.
You can load more than services in your Medusa backend. You can load the Entity Manager, logger instance, and much more.
MedusaContainer
To manage dependency injections, Medusa uses Awilix. Awilix is an NPM package that implements dependency injection in Node.js projects.
When you run the Medusa backend, a container of the type MedusaContainer
is created. This type extends the AwilixContainer object.
The backend then registers all important resources in the container, which makes them accessible in classes and API Routes.
Registered Resources
The Medusa backend scans the core Medusa package, plugins, and your files in the dist
directory and registers the following resources:
The Lifetime column indicates the lifetime of a service. Other resources that aren't services don't have a lifetime, which is indicated with the -
in the column. You can learn about what a lifetime is in the Create a Service documentation.
Resource | Description | Registration Name | Lifetime |
---|---|---|---|
Configurations | The configurations that are exported from |
| - |
Services | Services that extend the | Each service is registered under its camel-case name. For example, the | Core services by default have the |
Entity Manager | An instance of Typeorm’s Entity Manager. |
| - |
Logger | An instance of Medusa CLI’s logger. You can use it to log messages to the terminal. |
| - |
Single Payment Processor | An instance of every payment processor that extends the | Every payment processor is registered under two names:
| By default, it's |
All Payment Processors | An array of all payment processor that extend the |
|
|
Single Fulfillment Provider | An instance of every fulfillment provider that extends the | Every fulfillment provider is registered under two names:
| By default, it's |
All Fulfillment Providers | An array of all fulfillment providers that extend the |
|
|
Single Notification Provider | An instance of every notification provider that extends the | Every notification provider is registered under two names:
| By default, it's |
All Notification Providers | An array of all notification providers that extend the |
|
|
File Service | An instance of the class that extends the | The file service is registered under two names:
| By default, it's |
Search Service | An instance of the class that extends the | The search service is registered under two names:
| By default, it's |
Single Tax Provider | An instance of every tax provider that extends the | The tax provider is registered under two names:
| By default, it's |
All Tax Providers | An array of every tax provider that extends the |
|
|
Oauth Services | An instance of every service that extends the | Each Oauth Service is registered under its camel-case name followed by | By default, it's |
Feature Flag Router | An instance of the |
| - |
Redis | An instance of the Redis client. If Redis is not configured, a fake Redis client is registered. |
| - |
Single Entity | An instance of every entity. | Each entity is registered under its camel-case name followed by Model. For example, the | - |
All Entities | An array of all database entities that is passed to Typeorm when connecting to the database. |
| - |
Repositories | An instance of each repository. | Each repository is registered under its camel-case name. For example, | - |
Single Batch Job Strategy | An instance of every class extending the | Each batch job strategy is registered under three names:
| - |
All Batch Job Strategies | An array of all classes extending the |
| - |
Tax Calculation Strategy | An instance of the class implementing the |
| - |
Cart Completion Strategy | An instance of the class extending the |
| - |
Price Selection Strategy | An instance of the class implementing the |
| - |
Strategies | An instance of strategies that aren’t of the specific types mentioned above and that are under the | Its camel-case name. | - |
Resolve Resources
This section covers how to resolve resources from the dependency container to use them in API Routes and classes in general.
In API Routes
To resolve resources, such as services, in API Routes, use the MedusaRequest
object's scope.resolve
method. The method receives the registration name of the resource as a parameter.
For example:
Please note that in API Routes some resources, such as repositories, aren't available. Refer to the repositories documentation to learn how you can load them.
In Subscribers
To resolve resources, such as services, in subscriber handler functions, use the container
property of the handler function's parameter. The container
has a method resolve
which accepts the registration name of a resource as a parameter.
For example:
import {
ProductService,
type SubscriberConfig,
type SubscriberArgs,
} from "@medusajs/medusa"
export default async function productUpdateHandler({
data, eventName, container, pluginOptions,
}: SubscriberArgs<Record<string, string>>) {
const productService: ProductService = container.resolve(
"productService"
)
// ...
}
// ...
In Classes
In classes such as services or strategies, you can load resources in the constructor function using dependency injection. The constructor receives an object of dependencies as a first parameter. Each dependency in the object should use the registration name of the resource that should be injected to the class.
For example: