Dependency Injection

:::info Coming Soon Detailed dependency injection documentation is under development. :::

Zelt uses needle-di under the hood for dependency injection, providing a lightweight and type-safe DI container.

Quick Overview

@Injectable()
export class DatabaseService {
  query(sql: string) {
    // ...
  }
}

@Injectable()
export class UserRepository {
  constructor(private db = inject(DatabaseService)) {}

  findAll() {
    return this.db.query('SELECT * FROM users');
  }
}

See the Services documentation for practical usage patterns.

Decorator Composition

Zelt provides utilities to combine multiple decorators into a single meta-decorator. This is useful for creating reusable custom decorators that bundle related functionality.

composeClassDecorators

Combines multiple class decorators into one.

const GraphqlController = (path: string) =>
  composeClassDecorators(
    Controller(path),
    createClassDecorator({ decorator: 'GraphqlController' })
  );

@GraphqlController('/api')
class UserResolver {}

composeMethodDecorators

Combines multiple method decorators into one.

const Controller = () => createClassDecorator({});
const Route = (method: string, path: string) =>
  createMethodDecorator({ decorator: 'Route', method, path });

const Query = (path: string) =>
  composeMethodDecorators(
    Route('GET', path),
    createMethodDecorator({ decorator: 'Query' })
  );

@Controller()
class TestController {
  @Query('/users')
  getUsers() {}
}

composePropertyDecorators

Combines multiple property decorators into one.

const Entity = () => createClassDecorator({});
const Column = (opts?: { nullable?: boolean }) =>
  createPropertyDecorator({ decorator: 'Column', nullable: opts?.nullable ?? false });
const Searchable = () => createPropertyDecorator({ decorator: 'Searchable' });

const SearchableColumn = (opts?: { nullable?: boolean }) =>
  composePropertyDecorators(Column(opts), Searchable());

@Entity()
class User {
  @SearchableColumn()
  name!: string;
}

How It Works

• Props are merged: Each decorator's props are appended to the metadata in order
• Trace points to usage: The source position trace points to where the composed decorator is applied (the class definition for composeClassDecorators, the method for composeMethodDecorators, or the property for composePropertyDecorators), not where the decorator factory was defined
• Use case: Create custom meta-decorators that bundle multiple decorators for cleaner, more semantic code