Ngrx 效果：输出未添加到动作流中

这个问题可以在这个 stackblitz 中重新解决。

这个例子很简单：用户选择一个种族和一个专业。

我希望在选择比赛时，专业被重置（ed ？）。

为此，我创建了一个效果：

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

但是该操作并未添加到流中。有人可以解释我为什么吗？（我是@ngrx 的新手，所以请仔细！）

PS：我知道我可以使用上一个问题的解决方案，但我正在尝试学习 ngrx 基础知识。

stackblitz 组件的代码：

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;
}