获取列表中带有标签的文档，按匹配总数排序 [英] Get documents with tags in list, ordered by total number of matches

问题描述

鉴于以下 MongoDB 文档集合:

Given the following MongoDB collection of documents :

{
 title : 'shirt one'
 tags : [
  'shirt',
  'cotton',
  't-shirt',
  'black'
 ]
},
{
 title : 'shirt two'
 tags : [
  'shirt',
  'white',
  'button down collar'
 ]
},
{
 title : 'shirt three'
 tags : [
  'shirt',
  'cotton',
  'red'
 ]
},
...

如何检索与标签列表匹配的项目列表，按匹配标签的总数排序?例如，给定这个标签列表作为输入:

How do you retrieve a list of items matching a list of tags, ordered by the total number of matched tags? For example, given this list of tags as input:

['shirt', 'cotton', 'black']

我想检索按匹配标签总数按降序排列的项目:

I'd want to retrieve the items ranked in desc order by total number of matching tags:

item          total matches
--------      --------------
Shirt One     3 (matched shirt + cotton + black)
Shirt Three   2 (matched shirt + cotton)
Shirt Two     1 (matched shirt)

在关系模式中，标签将是一个单独的表，您可以连接该表，计算匹配项并按计数排序.

In a relational schema, tags would be a separate table, and you could join against that table, count the matches, and order by the count.

但是，在 Mongo 中...?

But, in Mongo... ?

看来这种方法可行，

• 将输入标签分成多个IN"语句
• 通过将标签输入或"在一起来查询项目
  • 即where ('shirt' IN items.tags ) OR ('cotton' IN items.tags )
  • 例如，这将返回三个衬衫一号"实例、两个衬衫三号"实例等
  • 地图:发射(this._id, {...});
  • reduce:统计 _id 的总出现次数
  • finalize:按总数排序

  但我不清楚如何将其实现为 Mongo 查询，或者这是否是最有效的方法.

  But I'm not clear on how to implement this as a Mongo query, or if this is even the most efficient approach.

  推荐答案

  正如我在 在 MongoDB 中搜索数组并按匹配数排序

  可以使用聚合框架.

  假设

  • tags 属性是一个集合(没有重复的元素)
  • tags attribute is a set (no repeated elements)

  查询

  这种方法迫使您展开结果并使用展开的结果重新评估匹配谓词，因此它的效率非常低.

  This approach forces you to unwind the results and reevaluate the match predicate with unwinded results, so its really inefficient.

  db.test_col.aggregate(
      {$match: {tags: {$in: ["shirt","cotton","black"]}}}, 
      {$unwind: "$tags"}, 
      {$match: {tags: {$in: ["shirt","cotton","black"]}}},
      {$group: {
          _id:{"_id":1}, 
          matches:{$sum:1}
      }}, 
      {$sort:{matches:-1}}
  );
  

  预期结果

  {
      "result" : [
          {
              "_id" : {
                  "_id" : ObjectId("5051f1786a64bd2c54918b26")
              },
              "matches" : 3
          },
          {
              "_id" : {
                  "_id" : ObjectId("5051f1726a64bd2c54918b24")
              },
              "matches" : 2
          },
          {
              "_id" : {
                  "_id" : ObjectId("5051f1756a64bd2c54918b25")
              },
              "matches" : 1
          }
      ],
      "ok" : 1
  }
  

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