MongoDB，Java，按第一个数组条目排序 [英] MongoDB, Java, sort by first array entry

问题描述

我正在尝试通过Java API在MongoDB上执行查找后对值进行排序。结果列表包含以下条目：

I'm trying to sort values after executing a find on my MongoDB by Java API. The result list contains the following entries:

{
"_id": "P17-223",
"property": "P17",
"itemid": 223,
"labels": [
  {
    "language": "en",
    "value": "Greenland"
  },
  {
    "language": "es",
    "value": "Groenlandia"
  },
  {
    "language": "de",
    "value": "Grönland"
  }
]

}

我想按数组标签的第一个条目排序：

I want to sort by the first entry of the array labels:

  DBCursor cursor = getCollection().find(query);
  BasicDBObject orderBy = new BasicDBObject("labels[0].value", 1);
  cursor.sort(orderBy);

此代码不对游标值进行排序。你能帮助我吗？

Cursor values are not sorted by this code. Can you help me?

推荐答案

你试过吗

BasicDBObject orderBy = new BasicDBObject("labels.0.value", 1);

这并不明显，但是MongoDB文档却没有提到它。使用$符号匹配第一个项目，但指定数组元素编号似乎有效。如果有人有更好的文档描述行为，请回复链接。

It's not obvious, but the MongoDB documentation eludes to it. Using the $ sign matches the first item, but specifying the array element number seems to work. If anyone has a better document describing the behavior, please reply with the link.

来自文档

更新数组中的文档

Update Documents in an Array

The positional $ operator facilitates updates to arrays that contain embedded
documents. Use the positional $ operator to access the fields in the embedded
documents with the dot notation on the $ operator.

db.collection.update( { <query selector> }, { <update operator>: { "array.$.field" : value } } )

文档是这里

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