Providers এবং Dependency Injection

import { Injectable, NotFoundException } from "@nestjs/common";

export interface User {
  id: number;
  name: string;
  email: string;
}

@Injectable()
export class UsersService {
  private users: User[] = [
    { id: 1, name: "রহিম", email: "rahim@example.com" },
    { id: 2, name: "করিম", email: "karim@example.com" },
  ];

  findAll(): User[] {
    return this.users;
  }

  findOne(id: number): User {
    const user = this.users.find((u) => u.id === id);
    if (!user) throw new NotFoundException("User পাওয়া যায়নি");
    return user;
  }

  create(data: Omit<User, "id">): User {
    const user = { id: Date.now(), ...data };
    this.users.push(user);
    return user;
  }

  update(id: number, data: Partial<User>): User {
    const user = this.findOne(id);
    Object.assign(user, data);
    return user;
  }

  remove(id: number): void {
    this.findOne(id);
    this.users = this.users.filter((u) => u.id !== id);
  }
}

import { Controller } from "@nestjs/common";
import { UsersService } from "./users.service";

@Controller("users")
export class UsersController {
  // DI — constructor-এ inject
  constructor(private readonly usersService: UsersService) {}

  @Get()
  findAll() {
    return this.usersService.findAll();
  }
}

import { Injectable, Scope } from "@nestjs/common";

@Injectable({ scope: Scope.REQUEST })
export class RequestScopedService {
  private requestId = Math.random();
  getRequestId() { return this.requestId; }
}

import { Module } from "@nestjs/common";

@Module({
  providers: [
    {
      provide: "CONFIG",
      useFactory: () => ({
        port: process.env.PORT || 3000,
        env: process.env.NODE_ENV,
      }),
    },
  ],
})
export class AppModule {}

// ব্যবহার
constructor(
  @Inject("CONFIG") private config: { port: string; env: string },
) {}