将项目添加到Firebase数据库的列表中 [英] Add an item to a list in Firebase Database

问题描述

我具有以下Firebase数据库结构. uIds是List<String>的一种.我试图在uIds下添加另一个具有递增索引的uId. setValue()和updateChildren()将要求我检索现有数据，并且push()将添加具有随机生成的字符串作为键而不是递增索引的项.有没有不需要检索现有数据的简单方法?谢谢！

I have the following Firebase database structure. uIds is a type of List<String>. I am trying to add another uId under uIds with an incremented index. setValue() and updateChildren() would require me to retrieve existing data, and push() will add an item with a randomly generated string as a key instead of an incremented index. Is there a simpler way that does not require to retrieve the existing data? Thanks!

  "requests" : {
    "request001" : {
      "interests" : [ "x" ],
      "live" : true,
      "uIds" : [ "user1" ]  // <---- from this
    },
    "request002" : {
      "interests" : [ "y" ],
      "live" : true,
      "uIds" : [ "user2" ]
    }
  }

--------------------------------

抱歉，不确定.让我详细说明一下. 假设我拥有上述数据库，并想将其更新为以下数据库.

Sorry for the unclarity. Let me elaborate to make it clear. Say I have the above database and want to update it to the following.

  "requests" : {
    "-KSVYZwUQPfyosiyRVdr" : {
      "interests" : [ "x" ],
      "live" : true,
      "uIds" : [ "user1", "user2" ]   // <--- to this
    },
    "-KSl1L60g0tW5voyv0VU" : {
      "interests" : [ "y" ],
      "live" : true,
      "uIds" : [ "user2" ]
    }
  }

ishmaelMakitla的建议mDatabase.child("requests").child("request001").setValue(newRequest)将用"newRequest"覆盖"request001".因此，我应该检索"request001"的现有数据并将"user2"添加到列表uIds.会是这样的:

ishmaelMakitla's suggestion, mDatabase.child("requests").child("request001").setValue(newRequest), will overwrite the "request001" with "newRequest". So I should retrieve the existing data of "request001" and add "user2" to the list uIds. It will be something like this:

mDatabase.child("requests").child("request001").addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        Request newRequest = dataSnapshot.getValue(Request.class);
        newRequest.uIds.add("user2");
        mDatabase.child("requests").child("request001").setValue(newRequest);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}

});

但是我想知道是否需要此过程，因为我想做的只是将一个项目添加到列表uIds.

But I am wondering if this process is necessary since what I am trying to do is simply to add one item to the list uIds.

推荐答案

建议您使用其他数据结构:

The Firebase documentation on creating data that scales proposes that you use a different data structure:

"requests" : {
  "-KSVYZwUQPfyosiyRVdr" : {
    "interests" : { "x": true },
    "live" : true,
    "uIds" : { 
      "user1": true, 
      "user2": true 
    }
  },
  "-KSl1L60g0tW5voyv0VU" : {
    "interests" : { "y": true },
    "live" : true,
    "uIds" : { 
      "user2": true 
    }
  }
}

以下是该数据结构更好地工作的一些原因:

Here are a few of the reasons why this data structure works better:

• 每个uid现在只能自动出现一次.实际上，我们已将数据建模为 set 而不是使用数组.
• 添加项目现在与ref.child("uUids").child("user3").setValue(true)
一样容易
• 您现在可以检查安全规则中是否存在uid.

• each uid can now automatically only appear once. We've essentially modeled our data as a set, instead of using an array.
• adding an item is now as easy as ref.child("uUids").child("user3").setValue(true)
• you can now check if a uid exists in your security rules.

我已经开始对自己重复:只要您发现自己在做array.contains("xyz")，就应该使用集合而不是数组.上面的"key": true映射是一种实现.在Firebase上设置.

I have started re-iterating to myself: whenever you find yourself doing array.contains("xyz"), you should probably be using a set instead of an array. The above mapping with "key": true is an implementation of a set on Firebase.

有些人可能认为数组是一种更有效的数据存储方式，但是对于Firebase而言，这是不正确的:

Some people may think arrays are a more efficient way of storing the data, but in the case of Firebase that is not true:

您看到的内容:

"uIds" : [ "user1", "user2" ]

Firebase存储什么:

What Firebase stores:

"uIds" : {
  "0": "user1",
  "1": "user2"
}

因此存储集合几乎相同:

So storing a set is pretty much the same:

"uIds" : { 
  "user1": true, 
  "user2": true 
}

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