NodeJS在检索Firebase实时数据库节点数据时的竞态条件

huangapple
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英文:

NodeJS race condition when retrieving Firebase realtime database node data

问题

以下是您要翻译的内容：

出现以下Node.js竞争条件问题（我认为是这样）。

我正在尝试获取池ID <当前＃> 是 <类型>

以下是我的代码，下面是输出：

  1. for (; currPool &lt;= lastPool;) {
  2.     console.log("Pool ID: " + currPool);
  3.     poolsRef.child(currPool).child("PoolType").once('value', function(snapshot) {
  4.         if (snapshot.exists()) {
  5.             const poolType = snapshot.val();
  6.             console.log("Pool ID:", currPool, "is a:", poolType, " Style PoolType");
  7.         }
  8.     });
  9.     currPool++;
  10. }

输出如下：

  1. Pool ID: 11018 is a: Survivor  Style PoolType
  2. Pool ID: 11019 is a: Pickem  Style PoolType
  3. Pool ID: 11020 is a: Pickem  Style PoolType
  4. Pool ID: 11021 is a: Pickem  Style PoolType
  5. Pool ID: 11022 is a: Pickem  Style PoolType
  6. Pool ID: 11023 is a: Survivor  Style PoolType

如何让它显示：

  1. Pool ID: 11018 is a: Survivor  Style PoolType
  2. Pool ID: 11019 is a: Pickem  Style PoolType
  3. Pool ID: 11020 is a: Pickem  Style PoolType
  4. Pool ID: 11021 is a: Pickem  Style PoolType
  5. Pool ID: 11022 is a: Pickem  Style PoolType
  6. Pool ID: 11023 is a: Survivor  Style PoolType
英文:

Having an issue with the following nodejs race condition (i believe it called).

I am trying to get the Pool ID <current #> is a <type>

Below is my code and below that is the output:

  1. for(;currPool&lt;=lastPool;) {
  3.     console.log(&quot;Current Pool ID: &quot; + currPool);
  5.     poolsRef.child(currPool).child(&quot;PoolType&quot;).once(&#39;value&#39;, function(snapshot) {
  6.         
  7.         if (snapshot.exists()) {
  8.         
  9.             const poolType = snapshot.val();
  10.             //
  11.             console.log(&quot;Pool ID:&quot;, currPool, &quot;is a:&quot;, poolType , &quot; Style PoolType&quot;);
  13.          }
  15.     });
  17.     currPool++;
  19. }

The output is as follows:

  1. Current Pool ID: 11018
  2. Current Pool ID: 11019
  3. Current Pool ID: 11020
  4. Current Pool ID: 11021
  5. Current Pool ID: 11022
  6. Current Pool ID: 11023
  7. Pool ID: 11024 is a: Survivor  Style PoolType
  8. Pool ID: 11024 is a: Pickem  Style PoolType
  9. Pool ID: 11024 is a: Pickem  Style PoolType
  10. Pool ID: 11024 is a: Pickem  Style PoolType
  11. Pool ID: 11024 is a: Pickem  Style PoolType
  12. Pool ID: 11024 is a: Survivor  Style PoolType

How do i get it to display :

  1. Pool ID: 11018 is a: Survivor  Style PoolType
  2. Pool ID: 11019 is a: Pickem  Style PoolType
  3. Pool ID: 11020 is a: Pickem  Style PoolType
  4. Pool ID: 11021 is a: Pickem  Style PoolType
  5. Pool ID: 11022 is a: Pickem  Style PoolType
  6. Pool ID: 11023 is a: Survivor  Style PoolType

答案1

得分: 1

你在循环内部使用了回调函数。这是一个有很多问题的做法，像这里提到的那样。使用for循环来执行任务并不理想。如果想使用for循环，在for语句中加入currPool++。或者使用while循环：

  1. while (currPool <= lastPool) {
  2.     // 代码的其余部分
  3.     currPool++
  4. }

根据文档，.on接受一个回调函数，而.once可以接受回调函数，但也返回一个Promise，这将有助于简化你的代码并解决异步问题：

  1. ;(async () => {
  2.     while (currPool <= lastPool) {
  3.         console.log("当前池ID：", currPool)
  4.         const snapshot = await poolsRef.child(currPool)
  5.             .child("PoolType")
  6.             .once("value")
  7.         if (snapshot.exists()) {
  8.             const poolType = snapshot.val()
  9.             console.log("池ID：", currPool, "是：", poolType, "风格的PoolType")
  10.         }
  11.         currPool++
  12.     }
  13. })
英文:

You've got a callback inside a loop. There are lots of questions around about that issue, like this one, but getting your code to work with a for loop isn't ideal.

You're using a for loop to do the job a while loop. If you want to use a for loop, currPool++ in the for statement. Or use a while loop instead:

  1. while (currPool &lt;= lastPool) {
  2.     // rest of the code
  3.     currPool++
  4. }

And according to the docs, .on takes a callback, while .once can take a callback, but also returns a Promise, which would help flatten your code and fix the async issue:

  1. ;(async () =&gt; {
  2.     while (currPool &lt;= lastPool) {
  3.         console.log(&quot;Current Pool ID: &quot;, currPool)
  4.         const snapshot = await poolsRef.child(currPool)
  5.             .child(&quot;PoolType&quot;)
  6.             .once(&quot;value&quot;)
  7.         if (snapshot.exists()) {
  8.             const poolType = snapshot.val()
  9.             console.log(&quot;Pool ID:&quot;, currPool, &quot;is a:&quot;, poolType , &quot; Style PoolType&quot;)
  10.         }
  11.         currPool++
  12.     }
  13. })

huangapple
  • 本文由 发表于 2023年5月7日 09:38:48
  • 转载请务必保留本文链接：https://go.coder-hub.com/76191878.html
  • firebase
  • firebase-realtime-database
  • node.js
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