Angular/w ngrx - 连续的API调用

Question

我正在Angular 4 app中实现ngrx.redux相关部分的代码结构基于ngrx repo(https://github.com/ngrx/example-app)的示例应用程序.现在我想知道如何实现这样的东西:

1. 我有某种实体的形式.
2. 在提交时,我发送POST请求到API,只有该实体的名称.
3. 作为回应,我获得了新创建的实体的ID.
4. 紧接着,我想发送第二个请求与剩余的表单值和id我刚刚得到.

我应该在哪里以及如何提出第二个请求？

Answer 1

如何实现连续的API调用取决于调用应该有多紧密.
我的意思是,您是将这两个调用视为单个"事务",其中两个请求都必须成功,才能成功更改您的状态.

显然,如果第一个请求失败,则无法启动第二个请求,因为它依赖于第一个请求的数据.但...

当第一个请求成功并且第二个请求失败时会发生什么？

您的应用程序是否可以继续使用id第一个请求而没有第二个请求,或者它是否会以不一致的状态结束？

我将介绍两种情况:

1. 场景1:当任一请求失败时,您将其视为整个"事务"失败,因此不关心哪个请求失败.
2. 场景2:当请求1失败时,将不执行请求2.当请求2失败时,请求1仍将被视为成功.

场景1

由于两个请求都必须成功,因此您可以将两个请求视为仅一个请求.在这种情况下,我建议隐藏服务中的连续调用(这种方法不是特定于ngrx/redux,它只是简单的RxJs):

@Injectable()
export class PostService {
    private API_URL1 = 'http://your.api.com/resource1';
    private API_URL2 = 'http://your.api.com/resource2';

    constructor(private http: Http) { }

    postCombined(formValues: { name: string, age: number }): Observable<any> {      
        return this.http.post(this.API_URL1, { name: formValues.name })
            .map(res => res.json())
            .switchMap(post1result =>
                this.http.post(this.API_URL2, {
                 /* access to post1result and formValues */
                  id: post1result.id,
                  age: formValues.age,
                  timestamp: new Date()
                })
                .map(res => res.json())
                .mergeMap(post2result => Observable.of({
                  /* access to post1result and post2result */
                  id: post1result.id,
                  name: post1result.name,
                  age: post2result.age,
                  timestamp: post2result.timestamp
               })
            );
    }
}

现在,您可以像使用postCombinedngrx-example-app中展示的任何其他服务方法一样使用-method.

• 如果任一请求失败,该服务将抛出一个错误,您可以捕获并处理您的效果.
• 如果两个请求都成功,您将获得内部定义的数据mergeMap.如您所见,可以从两个请求响应中返回合并数据.

情景2

使用这种方法,您可以区分两个请求的结果,如果其中一个请求失败,则会有不同的反应.我建议将两个调用分解为独立操作,以便您可以独立地减少每个案例.

首先,该服务现在有两个独立的方法(这里没什么特别的):

post.service.ts

@Injectable()
export class PostService {
    private API_URL1 = 'http://your.api.com/resource1';
    private API_URL2 = 'http://your.api.com/resource2';

    constructor(private http: Http) { }

    post1(formValues: { name: string }): Observable<{ id: number }> {
        return this.http.post(this.API_URL1, formValues).map(res => res.json());
    }

    post2(receivedId: number, formValues: { age: number }): Observable<any> {
        return this.http.post(this.API_URL2, {
          id: receivedId,
          age: formValues.age,
          timestamp: new Date()
        })
        .map(res => res.json());
  }
}

接下来为两个请求定义请求,成功和失败操作:

post.actions.ts

import { Action } from '@ngrx/store';

export const POST1_REQUEST = 'POST1_REQUEST';
export const POST1_SUCCESS = 'POST1_SUCCESS';
export const POST1_FAILURE = 'POST1_FAILURE';
export const POST2_REQUEST = 'POST2_REQUEST';
export const POST2_SUCCESS = 'POST2_SUCCESS';
export const POST2_FAILURE = 'POST2_FAILURE';

export class Post1RequestAction implements Action {
    readonly type = POST1_REQUEST;
    constructor(public payload: { name: string, age: number }) { }
}

export class Post1SuccessAction implements Action {
    readonly type = POST1_SUCCESS;
    constructor(public payload: { id: number }) { }
}

export class Post1FailureAction implements Action {
    readonly type = POST1_FAILURE;
    constructor(public error: any) { }
}

export class Post2RequestAction implements Action {
    readonly type = POST2_REQUEST;
    constructor(public payload: { id: number, name: string, age: number}) { }
}

export class Post2SuccessAction implements Action {
    readonly type = POST2_SUCCESS;
    constructor(public payload: any) { }
}

export class Post2FailureAction implements Action {
    readonly type = POST2_FAILURE;
    constructor(public error: any) { }
}

export type Actions
    = Post1RequestAction
    | Post1SuccessAction
    | Post1FailureAction
    | Post2RequestAction
    | Post2SuccessAction
    | Post2FailureAction

现在我们可以定义在调度请求操作时将运行的两个效果,然后根据服务调用的结果调度成功或失败操作:

post.effects.ts

import { PostService } from '../services/post.service';
import * as post from '../actions/post';

@Injectable()
export class PostEffects {
    @Effect()
    post1$: Observable<Action> = this.actions$
        .ofType(post.POST1_REQUEST)
        .map(toPayload)
        .switchMap(formValues => this.postService.post1(formValues)
            .mergeMap(post1Result =>
                Observable.from([
                    /*
                     * dispatch an action that signals that
                     * the first request was successful
                     */
                    new post.Post1SuccessAction(post1Result),

                    /*
                     * dispatch an action that triggers the second effect
                     * as payload we deliver the id we received from the first call
                     * and any other values the second request needs
                     */
                    new post.Post2RequestAction({
                        id: post1Result.id,
                        name: formValues.name,
                        age: formValues.age
                    })
                ])
            )
            .catch(err => Observable.of(new post.Post1FailureAction(err)))
        );

    @Effect()
    post2$: Observable<Action> = this.actions$
        /*
         * this effect will only run if the first was successful
         * since it depends on the id being returned from the first request
         */
        .ofType(post.POST2_REQUEST)
        .map(toPayload)
        .switchMap(formValuesAndId =>
            this.postService.post2(
                /* we have access to the id of the first request */
                formValuesAndId.id,
                /* the rest of the form values we need for the second request */
                { age: formValuesAndId.age }
            )
            .map(post2Result => new post.Post2SuccessAction(post2Result))
            .catch(err => Observable.of(new post.Post2FailureAction(err)))
        );

    constructor(private actions$: Actions, private postService: PostService) { }
}

请注意mergeMap与Observable.from([..])第一个效果结合使用.它允许您调度Post1SuccessAction可以减少(通过减速器)以及Post2RequestAction将触发第二个效果运行的.如果第一个请求失败,第二个请求将不会运行,因为Post2RequestAction未调度.

如您所见,以这种方式设置操作和效果允许您独立于其他请求对失败的请求做出反应.

要开始第一个请求,您只需Post1RequestAction在提交表单时发送一个请求即可.类似this.store.dispatch(new post.Post1RequestAction({ name: 'Bob', age: 45 }))的例子.