A module is a class annotated with a @Module() decorator. The @Module() decorator provides metadata that Danet makes use of to organize the application structure.

Each application has at least one module, a root module. The root module is the starting point Danet uses to build the application graph - the internal data structure Danet uses to resolve module and provider relationships and dependencies. While very small applications may theoretically have just the root module, this is not the typical case. We want to emphasize that modules are strongly recommended as an effective way to organize your components. Thus, for most applications, the resulting architecture will employ multiple modules, each declaring a closely related set of capabilities.

The @Module() decorator takes a single object whose properties describe the module:

The module does not encapsulate injectables. This means that you can inject injectables from any module as long as it has been resolved.

This will change in the future.

Feature modules ​

The TodoController and TodoService belong to the same application domain. As they are closely related, it makes sense to move them into a feature module. A feature module simply organizes code relevant for a specific feature, keeping code organized and establishing clear boundaries. This helps us manage complexity and develop with SOLID principles, especially as the size of the application and/or team grow.

To demonstrate this, we'll create the TodoModule.

import { Module } from 'jsr:@danet/core';
import { TodoController } from './todo.controller';
import { TodoService } from './todo.service';

@Module({
  controllers: [TodoController],
  injectables: [TodoService],
})
export class TodoModule {}

Above, we defined the TodoModule in the todo.module.ts file, and moved everything related to this module into the todo directory. The last thing we need to do is import this module into the root module (the AppModule, defined in the app.module.ts file).

import { Module } from 'jsr:@danet/core';
import { TodoModule } from './todo/todo.module';

@Module({
  imports: [TodoModule],
})
export class AppModule {}

Shared modules ​

In Danet, modules are singletons by default, and thus you can share the same instance of any provider between multiple modules effortlessly.

Every module is automatically a shared module. Once created it can be reused by any module. Let's imagine that we want to share an instance of the TodoService between several other modules. In order to do that, nothing has to be done, any module that imports the TodoModule has access to the TodoService and will share the same instance with all other modules that import it as well.

Global modules ​

Like in Angular injectables are registered in the global scope. Once defined, they're available everywhere.

Dynamic modules ​

The Danet module system includes a powerful feature called dynamic modules. This feature enables you to easily create customizable modules that can register and configure providers dynamically. Dynamic modules are covered extensively here. In this chapter, we'll give a brief overview to complete the introduction to modules.

Following is an example of a dynamic module definition for a DatabaseModule:

import { Module, DynamicModule } from 'jsr:@danet/core';
import { createDatabaseProviders } from './database.providers';
import { Connection } from './connection.provider';

@Module({
  providers: [Connection],
})
export class DatabaseModule {
  static forRoot(entities = [], options?): DynamicModule {
    const providers = createDatabaseProviders(options, entities);
    return {
      module: DatabaseModule,
      providers: providers,
      exports: providers,
    };
  }
}

This module defines the Connection provider by default (in the @Module() decorator metadata), but additionally - depending on the entities and options objects passed into the forRoot() method - exposes a collection of providers, for example, repositories. Note that the properties returned by the dynamic module extend (rather than override) the base module metadata defined in the @Module() decorator. That's how both the statically declared Connection provider and the dynamically generated repository providers are exported from the module.

The DatabaseModule can be imported and configured in the following manner:

import { Module } from 'jsr:@danet/core';
import { DatabaseModule } from './database/database.module';
import { User } from './users/entities/user.entity';

@Module({
  imports: [DatabaseModule.forRoot([User])],
})
export class AppModule {}

If you want to in turn re-export a dynamic module, you can omit the forRoot() method call in the exports array:

The Dynamic modules chapter covers this topic in greater detail.