Angular Firebase-将两个Observable合并为一个 [英] Angular Firebase - merge two Observables into one

问题描述

在这里苦苦挣扎太久了.我在Firebase中有两个表:

Struggling a bit too long here. I have two tables in Firebase:

accounts
  LJHGGKJH
   prop1: 'val'
   prop2: 'val'
  IUYIUTJF
   prop1: 'val'
   prop2: 'val'

locations_per_account
  LJHGGKJH
   0: [1, 5, 6]
  IUYIUTJF
   0: [5, 2, 8]

您会看到 accounts 项的唯一键指向 locations_per_account 项的唯一键-如果它们匹配，则它们属于同一用户.

As you see accounts item's unique key points to locations_per_account item's unique key - if they match they belongs to the same user.

现在，我想在服务中建立一种方法，使我可以观察到每个帐户及其位置，因此可以在模板中使用 async 管道并提取数据.

Now I want to make one method in my service which would provide me observable of every account and its locations, so I could use async pipe in my template and extract the data.

我在这里拥有所有帐户:

Here I get all accounts:

  getAllAccounts() {
    return this.afDb.list('accounts/', {
      query: {
        orderByChild: 'hasAccount',
        equalTo: true
      }
    })      
  }

我在这里获得特定帐户的位置:

Here I get locations of particular account:

  getAccountLocations(optionalUid : string) {
    let uid : any;
    this.authService.authInfo$.subscribe(val => uid = val.$uid); 
    if (typeof optionalUid === 'undefined')
      return this.afDb.object('locations-per-account/' + uid);
    return this.afDb.object('locations-per-account/' + optionalUid);
  } 

因此，我需要将这些流合并为一个，并通过合并来构造返回对象的新形状.

So I need to merge these streams into one and by merging I should construct the new shape of returning object.

(两个表的顺序是对称的(如果那是正确的词)，但是我不确定将来是否会保持不变，所以我想检查两个键是否匹配).

(the order of both tables is symmetric (if thats the right word), but I am not sure if it will stay the same in the future, so i would like to check if both keys match).

还要注意-如您所见，我可以向每个帐户添加locations数组，但是我在单独的表中执行此操作，因为我尝试使Firebase数据库尽可能平坦，以避免出现全表扫描"之类的事情.如果有任何想法，请提出建议-我在建立数据库方面还很陌生.

Also to note - as you see, I could add locations array to every account, but I do it in separate table because I try to make my Firebase database as flat as possible, to avoid things like "Full table scan". Please advice if any thoughts - I am pretty new in building databases.

推荐答案

使用forkJoin等待两个查询，然后将两个集合映射到id上:

Use forkJoin to wait for both queries, then map the two sets together on id:

Rx.Observable.forkJoin([accounts$, locations$]).subscribe(results => {
  const [accounts, locations] = results
  const joined = accounts.map(account => { 
    return {
      id: account.id,
      prop1: account.prop1,
      prop2: account.prop2,
      locations: locations.filter(location => location.id === account.id)[0].loc            };
  })
  console.log(joined);
});

这假定Firebase为每个查询都发出一个值，每个查询都是一个数组(我认为确实是从文档中得出的一个数组).

This presumes that Firebase is emitting a single value for each query, each of which is an array (which I think it does, from the docs).

还假定每个ID都有一个帐户和位置，否则，映射将变得更加复杂.

Also presumes one account and location per id, if not then the mapping would need to get more complicated.

这是一个模拟场景的CodePen. CodePen

Here's a CodePen which simulates the scenario. CodePen

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