Nest无法解析AuthService依赖，排查后仍未找到原因求助

报错信息 #

Error: Nest can't resolve dependencies of the AuthService (?). Please make sure that the argument dependency at index [0] is available in the AuthModule context.

Potential solutions:

• Is AuthModule a valid NestJS module?
• If dependency is a provider, is it part of the current AuthModule?
• If dependency is exported from a separate @Module, is that module imported within AuthModule?
  @Module({
  imports: [ /* the Module containing dependency */ ]
  })

相关代码 #

AppModule #

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

import { AuthModule } from './auth';

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

AuthModule #

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

import { UserModule } from '@/user';
import { AuthController } from './auth.controller';
import { AuthService } from './auth.service';

@Module({
  controllers: [AuthController],
  providers: [AuthService],
  imports: [UserModule]
})
export class AuthModule {}

AuthService #

import { Inject, Injectable } from '@nestjs/common';

import { UserService } from '@/user';

@Injectable()
export class AuthService {
  constructor(@Inject() private readonly userService: UserService) {}
}

UserModule #

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

import { UserService } from './user.service';

@Module({
  providers: [UserService],
  exports: [UserService]
})
export class UserModule {}

UserService #

import { Injectable } from '@nestjs/common';

@Injectable()
export class UserService {}

问题原因及解决方法 #

问题出在AuthService的构造器参数上——你给UserService添加了不必要的@Inject()装饰器。

对于类类型的提供者，NestJS会自动根据类的类型完成依赖注入，无需手动添加@Inject()。当你使用空的@Inject()时，Nest会尝试寻找无指定标识的依赖，而UserService的默认标识是它自身的类，两者无法匹配，因此触发报错。

只需去掉构造器参数上的@Inject()即可解决问题：

import { Injectable } from '@nestjs/common';

import { UserService } from '@/user';

@Injectable()
export class AuthService {
  constructor(private readonly userService: UserService) {}
}

修改后，Nest就能正确识别UserService作为依赖，从已导入的UserModule中获取对应的实例。

内容的提问来源于stack exchange，提问作者lian