如何在 MongoDB 查询中过滤和映射文档数组? [英] How to filter and map array of documents in MongoDB query?

问题描述

所以我的人员集合中有这些文件:

So I've got these documents in my people collection:

{
        "_id" : ObjectId("595c0630939a8ae59053a9c3"),
        "name" : "John Smith",
        "age" : 37,
        "location" : "San Francisco, CA",
        "hobbies" : [
                {
                        "name" : "Cooking",
                        "type" : "Indoor",
                        "regular" : true
                },
                {
                        "name" : "Baseball",
                        "type" : "Outdoor",
                        "regular" : false
                }
        ]
}
{
        "_id" : ObjectId("595c06b7939a8ae59053a9c4"),
        "name" : "Miranda Thompson",
        "age" : 26,
        "location" : "Modesto, CA",
        "hobbies" : [
                {
                        "name" : "Lego building",
                        "type" : "Indoor",
                        "regular" : false
                },
                {
                        "name" : "Yoga",
                        "type" : "Indoor",
                        "regular" : false
                }
        ]
}
{
        "_id" : ObjectId("595c078e939a8ae59053a9c5"),
        "name" : "Shelly Simon",
        "age" : 26,
        "location" : "Salt Lake City, UT",
        "hobbies" : [
                {
                        "name" : "Hunting",
                        "type" : "Outdoor",
                        "regular" : false
                },
                {
                        "name" : "Soccer",
                        "type" : "Outdoor",
                        "regular" : true
                }
        ]
}

我正在尝试仅将我的爱好"数组过滤为常规爱好并投影字段_id、姓名、年龄和爱好的名称和类型.

I am trying to filter my "hobbies" array only to regular hobbies AND project the fields _id, name, age and hobby's name and type.

我希望我的输出是这样的:

I want my output to be something like this:

{
        "_id" : ObjectId("595c0630939a8ae59053a9c3"),
        "name" : "John Smith",
        "age" : 37,
        "hobbies" : [
                {
                        "name" : "Cooking",
                        "type" : "Indoor"
                }
        ]
}
{
        "_id" : ObjectId("595c06b7939a8ae59053a9c4"),
        "name" : "Miranda Thompson",
        "age" : 26,
        "hobbies" : []
}
{
        "_id" : ObjectId("595c078e939a8ae59053a9c5"),
        "name" : "Shelly Simon",
        "age" : 26,
        "hobbies" : [
                {
                        "name" : "Soccer",
                        "type" : "Outdoor"
                }
        ]
}

嗯...我可以在 mongo shell 中使用这个命令来实现这个输出:

Well... I can achieve this output using this command in mongo shell:

db.people.aggregate([
    { 
        $project: { 
            hobbies: { 
                $filter: { 
                    input: "$hobbies", 
                    as: "hobby", 
                    cond: { $eq: ["$$hobby.regular", true] } 
                }
            },
            name: 1,
            age: 1
        }
    }, 
    { 
        $project: { 
            "hobbies.name": 1, 
            "hobbies.type": 1, 
            name: 1,
            age: 1
        } 
    }
])

如您所见，我不得不依次使用两个 $project 运算符，我觉得这很难闻.

As you can see, I had to use two $project operators in sequence and I think this smells bad.

有没有办法通过另一个不按顺序使用相同运算符两次的查询来实现相同的结果?

Is there a way to achieve the same result with another query that does not use the same operator twice and in sequence?

推荐答案

您可以将 $filter 表达式包装在 $map 中以映射输出值.

You can wrap the $filter expression inside $map to map the output values.

db.people.aggregate([
  {
    "$project": {
      "name": 1,
      "age": 1,
      "hobbies": {
        "$map": {
          "input": {
            "$filter": {
              "input": "$hobbies",
              "as": "hobbyf",
              "cond": "$$hobbyf.regular"
            }
          },
          "as": "hobbym",
          "in": {
            "name": "$$hobbym.name",
            "type": "$$hobbym.type"
          }
        }
      }
    }
  }
])

这篇关于如何在 MongoDB 查询中过滤和映射文档数组?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！