javascript - 一对多 firebase 查询

Question

我正在尝试在 firebase 中创建一个一对多的数据结构。我的两个对象看起来像这样

category:
{
    cat1: { 
       name: 'Category 1'
    },
    cat2: {
       name: 'Category 2'
    }
}

products: 
{
   product1: {
     name: 'Product 1',
     categories: {
       cat1: true
     }
   },
   product2: {
     name: 'Product 2',
     categories: {
       cat1: true,
       cat2: true
     }
   }
}

现在，我将如何准确地查询此数据以获取包含所有类别的 product2？我已经尝试过这让我获得了所需的数据，但它似乎效率低下并且与文档似乎建议您这样做的方式不符....

    var ref = new Firebase("https://<my-firebase-url>/products/product2");
    var catRef = new Firebase("https://<my-firebase-url>/category");
    ref.once('value', function(snap) {
      var result = snap.val();
      Object.keys(result.categories).map(key => {
         catRef.child(key).once('value', function(category){
... //add category to array etc
         }
      }
    }

文档建议使用 child_added 事件，但是当我想要整个列表而不仅仅是添加子项时，这有什么意义呢？ ( https://www.firebase.com/docs/web/guide/structuring-data.html ):

    // List the names of all Mary's groups
var ref = new Firebase("https://docs-examples.firebaseio.com/web/org");
// fetch a list of Mary's groups
ref.child("users/mchen/groups").on('child_added', function(snapshot) {
  // for each group, fetch the name and print it
  String groupKey = snapshot.key();
  ref.child("groups/" + groupKey + "/name").once('value', function(snapshot) {
    System.out.println("Mary is a member of this group: " + snapshot.val());
  });
});

Answer 1

要获取属于 product2 的所有类别，您应该使用:

firebase.database().ref('products/product2/categories').on('child_added', snapshot => {
    firebase.database().ref('category/'+snapshot.key).on('value', snap => {
        console.log(snap.val().name + ' belongs to product2'); //Will print Category 1 and Category 2
    });
}):