如何在实现相同接口的不同实现之间切换作为嵌套js中服务的依赖项

Question

假设我们有 SomeService 接受 Iprovider 作为它的依赖项，我希望能够根据哪个控制器调用 SomeService 为 Iprovider 使用不同的实现。这在 Nestjs 中是如何实现的？

Answer 1

您可以使用Injection Token

这是一个示例代码：

此示例假定您已经设置了一个 NestJS 项目。这是一个简单的表格。显然，现实世界的实现可能会或可能不会不同

提供者接口

export interface IProvider{
  method();
}

实现

实施 1

import {IProvider} from '<path>';

//This token will be used to inject ProviderOne instance
export const ProviderOneToken = 'provider_one';

export class ProviderOne implements IProvider{
  public method(){
   console.log('ProviderOne');
 }
}

实施 2

import {IProvider} from '<path>';

//This token will be used to inject ProviderTwo instance
export const ProviderTwoToken = 'provider_two';

export class ProviderTwo implements IProvider{
  public method(){
   console.log('ProviderTwo');
 }
}

现在在App module，

//Imports....

@Module({
 providers:[
    {provide:ProviderOneToken, useClass:ProviderOne},
    {provide:ProviderTwoToken, useClass:ProviderTwo},
    // The service we are going to test the token based
    // injection
    ServiceToInject
  ]
})
export class AppModule{
}

ServiceToInject

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

@Injectable()
export class ServiceToInject{
  constructor(@Inject(ProviderOneToken) private readonly provider:IProvider){
 }
 public serviceMethod(){
  //Calls method of ProviderOne instance(service)
 // Logs = 'ProviderOne'
  this.provider.method();
 }
}

现在换掉令牌，

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

@Injectable()
export class ServiceToInject{
  // Changed provider token inside @Inject(<Here>).Rest are same
  constructor(@Inject(ProviderTwoToken) private readonly provider:IProvider){
 }
 public serviceMethod(){
  //Calls method of ProviderTwo instance(service)
  // Logs = 'ProviderTwo'
  this.provider.method();
 }
}

同一服务中的两个令牌：

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

@Injectable()
export class ServiceToInject{
  constructor(@Inject(ProviderTwoToken) private readonly providerTwo:IProvider,
@Inject(ProviderOneToken) private readonly providerOne:IProvider
){
 }
 public serviceMethod(){
  //Calls method of ProviderOne instance(service)
  // Logs = 'ProviderOne'
  this.providerOne.method();
  //Calls method of ProviderTwo instance(service)
  // Logs = 'ProviderTwo'
  this.providerTwo.method();
 }
}

更新：

ServiceToInject 也可以是控制器。

ControllerOne

@Controller('one')
export class ControllerOne{
 constructor(@Inject(ProviderOneToken) private readonly providerOne:IProvider){}
 @Get()
 public getOne(){
 //Logs - 'ProviderOne'
 this.provider.method();
}
 
}

ControllerTwo

@Controller('two')
export class ControllerTwo{
 constructor(@Inject(ProviderTwoToken) private readonly providerOne:IProvider){}
 @Get()
 public getTwo(){
 //Logs - 'ProviderTwo'
 this.provider.method();
}
 
}