MongoDB按数组元素对文档进行排序

问题描述

我的文档结构如下:

{
    map: 'A',
    points: [
        {
            type: 'type1',
            distanceToSpawn: 110
        },
        {
            type: 'type4',
            distanceToSpawn: 40
        },
        {
           type: 'type6',
           distanceToSpawn: 30
        }
    ]
},
{
    map: 'B',
    points: [
        {
            type: 'type1',
            distanceToSpawn: 100
        },
        {
            type: 'type2',
            distanceToSpawn: 60
        },
        {
            type: 'type3',
            distanceToSpawn: 25
        }
    ]
},
{
    map: 'C',
    points: [
        {
            type: 'type2',
            distanceToSpawn: 90
        },
        {
            type: 'type3',
            distanceToSpawn: 1
        },
        {
            type: 'type6',
            distanceToSpawn: 76
        }
    ]
}

我想获取所有点类型为type1且按distanceToSpawn升序排序的地图.

I want to get all maps having point type type1 sorted by the distanceToSpawn in ascending order.

预期结果:

{
    map: 'B',
    points: [
        {
            type: 'type1',
            distanceToSpawn: 100
        }
    ]
},
{
    map: 'A',
    points: [
        {
            type: 'type1',
            distanceToSpawn: 110
        }
    ]
}

我尝试过类似的事情:

db.maps.find({'points.type': {$eq : 'type1'}}, {map: 1, 'points.$':1}).sort({'points.distanceToSpawn': 1}).limit(10)

但是，这并不是按升序对地图进行排序.

But this thing not sorting maps by ascending order.

谢谢.

推荐答案

您不能使用数组来做到这一点，这里的主要问题是因为您希望"sort"发生在匹配的元素上.如果要对这样的结果进行排序，则需要使用 .要么是:

You cannot do that with arrays, and the main problem here is because you want the "sort" to happen on the matched element. If you want to sort results like this then you need to use .aggregate() instead. Either as:

对于现代MongoDB版本:

For modern MongoDB versions:

db.maps.aggregate([
    { "$match": { "points.type": "type1" }},
    { "$addFields": {
        "order": {
            "$filter": {
              "input": "$points",
              "as": "p",
              "cond": { "$eq": [ "$$p.type", "type1" ] }
            }
        }
    }},
    { "$sort": { "order": 1 } }
])

对于MongoDB 2.6到3.0

For MongoDB 2.6 to 3.0

db.maps.aggregate([
   { $match: { 'points.type': 'type1' } },
    {
     $project: {
       points: {
        $setDifference: [
          {
            $map: {
              input: '$points',
              as: 'p',
              in: {
                $cond: [
                  { $eq: ['$$p.type', 'type1'] },
                  '$$p',
                  false,
                ]
              }
            }
          },
          [false]
        ]
      }
    }
  },
  { $sort: { 'points.distanceToSpawn': 1 } },
]);

在MongoDB 2.6之前的版本中效率较低:

Or less efficiently in versions prior to MongoDB 2.6:

db.maps.aggregate([
    { "$match": { "points.type": "type1" }},
    { "$unwind": "$points" },
    { "$match": { "points.type": "type1" }},
    { "$group": {
        "_id": "$_id",
        "points": { "$push": "$points" }
    }},
    { "$sort": { "points.ditanceToSpawn": 1 } }
])

这是匹配正确元素并在排序"操作中考虑它们的唯一方法.否则，默认的游标排序将考虑数组元素中与您选择的类型"不匹配的字段的值.

That's the only way to match the correct elements and have them considered in a "sort" operation. The default cursor sort will just otherwise consider the values for the field in the array elements that do not match your selected "type" instead.

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