1.8 providers

1. 生成providers

nest g service <name>

2. providers的注入方式

构造函数注入

@Injectable()
export class KeywordService {constructor(private readonly httpService: HttpService,private readonly pro: ProService,) {}
}

@Inject()注入

export class KeywordController {@Inject()private readonly httpService: HttpService;@Inject()private readonly keywordService: KeywordService;
}

3. providers注册

@Module({imports: [HttpModule.register({timeout: 5000,maxRedirects: 5,baseURL: 'http://localhost:3000',}),ProModule,],controllers: [KeywordController],providers: [KeywordService],
})
export class KeywordModule {}

4. 创建providers

a. 使用@Injectable()注解

b. providers完整写法

在module中注册时，一般使用简写，下面是providers的完整写法

providers: [{provide: CatsService,useClass: CatsService,},
];

c. 值提供者/value providers

//mock.ts
export class Mock {getHello(): string {return 'hello world';}
}//pro.module.ts
@Module({providers: [{provide: ProService,useValue: new Mock(),},],exports: [ProService],
})//Mock类要和ProService类拥有同样的方法，即Mock和ProService都有一个getHello()方法，则nest在解析时，会用Mock的getHello()方法替换掉ProService的getHello()方法

d. 非类提供者/Non-class-based provider tokens

//pro.module.ts
import { Mock } from './mock';
@Module({providers: [{provide: 'connect',useValue: new Mock(),},],exports: ['connect'],
})
export class ProModule {}
//mock.ts
export class Mock {getHello(): string {return 'hello world';}
}//注入
import { Mock } from '../pro/mock';
@Controller('keyword')
export class KeywordController {
@Inject('connect')private readonly mock: Mock;
}

e. 类提供者/useClass

import { ProService } from './pro.service';
@Module({providers: [{provide: 'ProService',useClass: ProService,},],exports: ['ProService'],
})
export class ProModule {}

或者用三元操作符来判断，返回特定的提供者

import { Module } from '@nestjs/common';
import { ProService } from './pro.service';
import { FactoryService } from './factory.service';let a;@Module({providers: [{provide: 'CONNECTION',useClass: a ? ProService : FactoryService,},],exports: ['CONNECTION'],
})
export class ProModule {}

f. 工厂提供者/factory providers

import { Module } from '@nestjs/common';
import { FactoryService } from './factory.service';@Module({providers: [FactoryService, //必须引入，或者直接引入FactoryModule{provide: 'CONNECTION',useFactory: (fac: FactoryService) => {return String(fac.getHello());},inject: [FactoryService],},],exports: ['CONNECTION'],
})
export class ProModule {}

或者

@Module({imports: [FactoryModule],providers: [{provide: 'CONNECTION',useFactory: (fac: FactoryService) => {return String(fac.getHello());},inject: [FactoryService],},],exports: ['CONNECTION'],
})

或者

import { Module } from '@nestjs/common';
import { FactoryService } from './factory.service';
import { FactoryModule } from './factory.module';
const connectionFactory = {provide: 'CONNECTION',useFactory: (optionsProvider: FactoryService) => {const options = optionsProvider.getHello();return String(options);},inject: [FactoryService],
};@Module({imports: [FactoryModule],providers: [connectionFactory, FactoryService],exports: [connectionFactory],
})

或者直接提供值

import { Module } from '@nestjs/common';
import { FactoryService } from './factory.service';
import { FactoryModule } from './factory.module';
const config = {data: {a: 1,b: 2,},
};
const connectionFactory = {provide: 'CONNECTION',useFactory: () => config,
};@Module({imports: [FactoryModule],providers: [connectionFactory, FactoryService],exports: [connectionFactory],
})

g.别名提供者

import { Module } from '@nestjs/common';
import { FactoryService } from './factory.service';
import { FactoryModule } from './factory.module';const TestService = {provide: 'Test',useExisting: FactoryService,
};
//TestService和FactoryService是同一个提供者
@Module({imports: [FactoryModule],providers: [FactoryService, TestService],exports: [TestService, FactoryService],
})

h.导出提供者

//可以导出令牌，也可以导出整个对象
exports: [‘Test', FactoryService]

i. 异步提供者

//在实例化依赖于(注入)这样一个提供程序的任何类之前，Nest将等待承诺的解决
{provide: 'ASYNC_CONNECTION',useFactory: async () => {const connection = await createConnection(options);return connection;},
}