Ngrx 效果：输出未添加到操作流中

Question

问题可以在this stackblitz中重新解决。

示例很简单：用户选择种族和专业。

我希望在选择种族时重置专长（ed ？）。

为此，我创建了一个效果：

@Effect()
raceChange = this.actions
  .pipe(
    ofType(SET_RACE),
    mapTo(new SetSpecialtyAction(''))
  );

但该操作并未添加到流中。有人可以解释一下为什么吗？ （我是 @ngrx 的新手，所以请彻底！）

PS：我知道我可以使用the solution from my previous question，但我正在尝试学习ngrx 基础知识。

stackblitz 组件代码：

import { Component } from '@angular/core';
import { Store, Action, ActionReducerMap } from '@ngrx/store';

@Component({
  selector: 'my-app',
  template: 
`
<select #race (change)="dispatchRace(race.value)" placeholder="Select a race">
  <option value="Elf">Elf</option>  
  <option value="Orc">Orc</option>  
  <option value="Dwarf">Dwarf</option>
</select>

  <select #spec (change)="dispatchSpecialty(spec.value)" placeholder="Select a specialty">
  <option value="Warrior">Warrior</option>  
  <option value="Berzerkrer">Berzerkrer</option>  
  <option value="Healer">Healer</option>  
</select>

<p>
  Current race: {{ (currentRace | async) || 'None' }}
</p>
<p>
  Current Spec: {{ (currentSpecialty | async) || 'None' }}  
</p>  
`
})
export class AppComponent {

  currentRace = this.raceStore.select('race');
  currentSpecialty = this.specStore.select('specialty');

  constructor(
    public raceStore: Store<RaceState>,
    public specStore: Store<SpecialtyState>,
    ) {
      this.currentRace.subscribe(x => console.log('race : ', x));
      this.currentSpecialty.subscribe(x => console.log('spec : ', x))
    }

  dispatchRace(race) {
    this.raceStore.dispatch(new SetRaceAction(race));
  }

  dispatchSpecialty(spec) {
    this.specStore.dispatch(new SetSpecialtyAction(spec));
  }
}


export const SET_RACE = '[RACE] Set';
export const SET_SPECIALTY = '[CLASS] Set';

export class SetRaceAction implements Action {
  readonly type = SET_RACE;
  constructor(public race: string) { }
}

export class SetSpecialtyAction implements Action {
  readonly type = SET_SPECIALTY;
  constructor(public specialty: string) { }
}

export function raceReducer(state: string = undefined, action: SetRaceAction): string {
  return action.race || state;
}

export function specialtyReducer(state: string = undefined, action: SetSpecialtyAction): string {
  return action.specialty || state;
}

export interface RaceState {
  readonly race: string;
}

export interface SpecialtyState {
  readonly specialty: string;
}

Answer 1

mapTo 将发射映射到字符串，使用 map 将映射到将被调度的动作。

为了使您的示例有效，我更改了两件事：

1- 将效果中的mapTo 替换为map：

@Effect()
raceChange = this.actions
   .pipe(
     ofType(SET_RACE),
     map(() => new SetSpecialtyAction(''))
);

2- 更改忽略空值的减速器：

export function specialtyReducer(state: string = undefined, action: SetSpecialtyAction): string {
  return action.specialty;
}

const value = '' || 'Not Empty';
console.log(value);

Here is a working fork.

您还可以使用 switchMap 映射到多个操作并返回一个数组 fo 操作：

@Effect()
raceChange = this.actions
   .pipe(
     ofType(SET_RACE),
     switchMap(() => [new SetSpecialtyAction(''), ...])
);

Answer 2

不需要效果，可以在专业reducer里面听race action：

export function specialtyReducer(state: string = undefined, action: SetSpecialtyAction | SetRaceAction): string {
  switch(action.type) {
    case SET_RACE:
      return '';
    default:
     return action.specialty || state;
  }
}