获取具有匹配计数条件的嵌套对象的文档 [英] Get documents with nested objects matching count condition

问题描述

我是mongo noob，正在与mongo集合一起工作，记录如下:

I am a mongo noob and am working with a mongo collection with records that look like so:

{
    "cats" [
        {
            "name": "fluffy",
            "color": "red",           
        }, 
        {
            "name": "snowball",
            "color": "white",           
        }, 
    ]
{

我想执行一个查询，以获取具有超过1只白猫的所有记录. MapReduce看起来很有前途，但似乎有些矫kill过正.感谢您的帮助.

I would like to perform a query that gets all records that have more than 1 white cats. MapReduce looks promising, but seems like overkill. Any help is appreciated.

推荐答案

您可以使用不需要使用 $where 运算符.

You can use the aggregation framework to do this. You don't need to use the $where operator.

db.collection.aggregate([
    { "$match": { "cats.color": "white" }},
    { "$project": { 
        "nwhite": { "$map": { 
            "input": "$cats", 
            "as": "c",
            "in": { "$cond": [
                { "$eq": [ "$$c.color", "white" ] },
                1, 
                0
            ]}
        }}, 
        "cats": 1
     }},
     { "$unwind": "$nwhite" }, 
     { "$group": { 
         "_id": "$_id", 
         "cats": { "$first": "$cats" }, 
         "nwhite": { "$sum": "$nwhite" }
     }},
    { "$match": { "nwhite": { "$gte" :2 } } } 
])

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