为什么Firebase集合似乎以空行开头? [英] Why do firebase collections seem to begin with a null row?

问题描述

我创建了一个简单的firebase数据集来测试一些REST调用(请参见下图).我想知道为什么，当我查询数据库中的集合时，firebase总是先返回空行，然后才返回实际​​行.这是导出数据时得到的信息.注意systems和system_types下的空行:

I've created a simple firebase data set to test some REST calls with (see the image below). I'm wondering why, when I query the collections in the database, firebase always return a null row first and then the actual rows. Here is what I get when I export the data. Notice the null rows under systems and system_types:

{
  "systems" : [ null, {
    "system_type_id" : 2,
    "name" : "Commodore 128",
    "id" : 1
  }, {
    "system_type_id" : 1,
    "name" : "Difference Engine",
    "id" : 2
  }, {
    "system_type_id" : 2,
    "name" : "Osborne",
    "id" : 3
  } ],
  "system_types" : [ null, {
    "name" : "Babbage",
    "id" : 1
  }, {
    "name" : "Von Neumann",
    "id" : 2
  } ]
}

推荐答案

Firebase会自动检测对象何时看起来像"数组，并相应地对其进行转换.由于'systems'和'system_types'的子级分别为1、2和3，因此Firebase会在输出时自动将其转换为数组.但是，由于您没有为索引0指定值，因此Firebase只是插入一个空元素.

Firebase automatically detects when an object 'looks like' an array, and converts it accordingly. Since 'systems' and 'system_types' have children of 1, 2, and 3, Firebase is automatically converting these to arrays at output time. However, since you didn't specify a value for index 0, Firebase is just inserting an empty element.

我建议您使用从零开始的ID，或者以非数字开头您的ID，因此我们知道它不是数组(例如:item1，item2，item3).

I'd suggest either using zero-based ID's, or perhaps starting your id's with something non-numeric so we know it's not an array (ie: item1, item2, item3).

您也可以忽略null元素-在Firebase中，null和不存在是同一件事.

You could also just ignore the null element -- In Firebase null and non-existent are the same thing.

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