Question

plans是具有两个字段的根集合：date和recipe。 recipe是对另一个名为recipes的根集合的引用。我正在尝试构建一个可观察的链，该链发出计划在指定日期范围内引用的食谱。

lookup(range: MealPlanRange): Observable<Recipe[]> {
    return this.db.collection('plans', ref=>ref
    .where('date', ">=", range.startDate )
    .where('date', "<=", range.endDate )
    ).valueChanges().pipe(
      // at this point, i have the plans i want, 
      //  but i don't know how to get the recipes
      switchMap(ps=>(/*how to get observable of recipes?*/)),
    );
  }

我尝试了this.db.doc(p[0].recipe)，但是没有返回可观察到的结果。我看着创建一个指定多个ID的查询，但这似乎是不可能的。有什么建议吗？

Answer 1

找到了：

lookup(range: MealPlanRange): Observable<Meal[]> {
    return this.db.collection('plans', ref => ref
      .where('date', ">=", range.startDate)
      .where('date', "<=", range.endDate)
    ).valueChanges().pipe(
      switchMap(ps => {
        // return empty array when no plans
        if(ps.length === 0) {
           return of([])
        }
        // for each plan, do a doc lookup and use valueChanges() to get observable of changes
        const recipes = ps.map(p => this.db.doc(p.recipe).valueChanges());
        // use combineLatest to get back into an array of recipes, 
        // any change to any recipe will re-emit
        return combineLatest(...recipes);
      }),
    ) as any;
  }

如何使用angularfire查询参考？

1 个答案: