使用Angular2/AngularFire2创建或增加值 [英] Create or increment a value with Angular2/AngularFire2

问题描述

我正在使用Angular 2和AngularFire 2与Firebase进行交互.在Firebase中，我有一个标签集合.我想为标签创建或增加编号.我正在使用的代码如下所示:

I'm using Angular 2 and AngularFire 2 to interact with Firebase. In Firebase I have a tags collection. I'd like to either create or increment the number for a tag. The code I'm using looks something like this:

let tagName = "angular";
let tagObs = this.af.database.object(`/tags/${tagName}`);
tagObs.subscribe(function(snapshot) {
    let newValue = (snapshot.$value) ? (snapshot.$value + 1) : 1;
    this.tagObs.set(newValue);
}.bind({ tagObs: tagObs ));

我不清楚为什么会这样，但这是行不通的.它会创建一个无限循环，使标签值不断增加.

It's not clear to me why, but this doesn't work. It creates an infinite loop that just keeps incrementing the tag value.

使用AngularFire 2，我应该如何为节点创建或增加一个值(在这种情况下为标签")?

Using AngularFire 2, how should I go about either creating or incrementing a value for a node (a "tag" in this case)?

这是带有胖箭头"功能的相同代码.存在相同的问题...无限循环.

Here is the same code with a "fat arrow" function. The same problem exists... an infinite loop.

let tagName = "angular";
let tagObs = this.af.database.object(`/tags/${tagName}`);
tagObs.subscribe((snapshot) => {
    let newValue = (snapshot.$value) ? (snapshot.$value + 1) : 1;
    tagObs.set(newValue);
});

更新#2:有效的代码

为了清楚起见，这是我最终使用的实际代码:

Update # 2: the code that worked

Just for the sake of clarity, this is the actual code I ended up using:

let tagObs = this.af.database.object(`/tags/${tagName}`);
tagObs.transaction(function(currentCount) {
  return currentCount + 1;
});

推荐答案

无限循环

您遇到了无限循环，因为每次tagObs引用接收到新值时都会调用subscribe方法，并且subscription函数使用set方法更改tabObs的值.

Infinite loop

You got an infinite loop because the subscribe method is called every time the tagObsreference receives a new value, and the subscribe function changes the value of tabObs with the set method.

Firebase针对这种情况提供了事务方法.这真的很有帮助，因为:

Firebase provides a transaction method for this situation. This is really helpful because:

transaction()用于将现有值修改为新值，以确保与同时写入同一位置的其他客户端没有冲突.

transaction() is used to modify the existing value to a new value, ensuring there are no conflicts with other clients writing to the same location at the same time.

tagObs.$ref.transaction(tagValue => {
  return tagValue ? tagValue + 1 : 1;
});

请务必注意，这是Firebase API(不是Angularfire2)中的一种方法，但是您仍然可以通过在提供的tagObs上调用$ref来访问这些方法，看起来像FirebaseObjectObservable.

It's important to note that this is a method from the Firebase API (not Angularfire2), but you can still access those methods by calling $ref on your provided tagObs which looks like a FirebaseObjectObservable.

这篇关于使用Angular2/AngularFire2创建或增加值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！