如何在NestJS普通实体类中注入Repository提供者（非TypeORM）

问题原因 #

你通过new UserAggregateEntity(user)手动创建实例，这类对象不在Nest的DI容器管理范围内，因此@Inject()装饰器不会生效，导致customerRepository为undefined。Nest的依赖注入仅对由DI容器实例化的类（比如标记了@Injectable()的服务）生效。

解决方案 #

方案1：将聚合类转为可注入，使用工厂提供者创建实例

把UserAggregateEntity标记为@Injectable()，通过工厂提供者处理它需要的user参数，同时注入CustomerRepository。

1. 修改聚合类，将依赖通过构造函数注入：

import { Injectable, Inject } from '@nestjs/common';
import { CustomerRepository } from './customer.repository';
import { UserEntity, CustomerEntity } from './entities';

@Injectable()
export class UserAggregateEntity {
  private customer: CustomerEntity;

  constructor(
    private user: UserEntity,
    @Inject(CustomerRepository)
    private readonly customerRepository: CustomerRepository,
  ) {}

  async createCustomer(customer: CustomerEntity): Promise<string> {
    customer.user = this.user.id;
    const savedCustomer = await this.customerRepository.create(customer);
    this.customer = savedCustomer;
    return customer.id;
  }
}

2. 在模块中配置工厂提供者，动态传入user参数：

import { Module, Provider } from '@nestjs/common';
import { UserAggregateEntity } from './user-aggregate.entity';
import { CustomerRepository } from './customer.repository';

export const UserAggregateFactory: Provider = {
  provide: 'UserAggregateFactory',
  useFactory: (customerRepository: CustomerRepository) => {
    return (user: UserEntity) => new UserAggregateEntity(user, customerRepository);
  },
  inject: [CustomerRepository],
};

@Module({
  providers: [CustomerRepository, UserAggregateFactory],
  exports: ['UserAggregateFactory'],
})
export class YourModule {}

3. 在服务中使用工厂创建聚合实例：

import { Inject, Injectable } from '@nestjs/common';
import { UserEntity, CustomerEntity } from './entities';

@Injectable()
export class UserService {
  constructor(
    @Inject('UserAggregateFactory')
    private readonly userAggregateFactory: (user: UserEntity) => UserAggregateEntity,
  ) {}

  async createCustomerForUser(user: UserEntity, customer: CustomerEntity) {
    const userAggregate = this.userAggregateFactory(user);
    return await userAggregate.createCustomer(customer);
  }
}

方案2：将业务逻辑移至服务层（推荐）

领域实体/聚合根应专注于业务规则和状态管理，不直接依赖Repository。把调用Repository的逻辑移到服务层，聚合根只处理核心业务逻辑：

1. 修改聚合类，移除Repository依赖：

export class UserAggregateEntity {
  private customer: CustomerEntity;

  constructor(private user: UserEntity) {}

  prepareCustomerForCreation(customer: CustomerEntity): CustomerEntity {
    customer.user = this.user.id;
    // 这里可添加业务规则校验、状态转换等逻辑
    return customer;
  }

  setCustomer(customer: CustomerEntity) {
    this.customer = customer;
  }
}

2. 在服务层注入Repository并处理持久化：

import { Injectable } from '@nestjs/common';
import { CustomerRepository } from './customer.repository';
import { UserEntity, CustomerEntity } from './entities';
import { UserAggregateEntity } from './user-aggregate.entity';

@Injectable()
export class UserService {
  constructor(private readonly customerRepository: CustomerRepository) {}

  async createCustomer(user: UserEntity, customer: CustomerEntity): Promise<string> {
    const userAggregate = new UserAggregateEntity(user);
    const preparedCustomer = userAggregate.prepareCustomerForCreation(customer);
    const savedCustomer = await this.customerRepository.create(preparedCustomer);
    userAggregate.setCustomer(savedCustomer);
    return savedCustomer.id;
  }
}

这种方式更符合领域驱动设计（DDD）原则，聚合根聚焦领域逻辑，数据持久化由基础设施层和应用服务层处理。

方案3：手动从DI容器获取依赖（不推荐）

如果必须在手动实例化的类中使用依赖，可以通过Nest全局容器获取，但会增加耦合度，不建议生产代码使用：

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { CustomerRepository } from './customer.repository';

// 启动时保存容器实例
let app;
async function bootstrap() {
  app = await NestFactory.create(AppModule);
  await app.listen(3000);
}
bootstrap();

export class UserAggregateEntity {
  private customerRepository: CustomerRepository;
  private customer: CustomerEntity;

  constructor(private user: UserEntity) {
    // 从容器中获取Repository实例
    this.customerRepository = app.get(CustomerRepository);
  }

  async createCustomer(customer: CustomerEntity): Promise<string> {
    customer.user = this.user.id;
    const savedCustomer = await this.customerRepository.create(customer);
    this.customer = savedCustomer;
    return customer.id;
  }
}

内容的提问来源于stack exchange，提问作者monguz