如何从 mongoDB 集合中获取数组? [英] How to get array from mongoDB collection?

问题描述

我在 mongoDB 中有这样的模式

i have such schema in mongoDB

{
    "key":"ru",
    "regions":[
        {
            "name":"moskovskaya",
            "cities":[
                {
                    "name":"moskva"
                },
                {
                    "name":"tula"
                }
            ]
        },
        {
            "name":"piterskaya",
            "cities":[
                {
                    "name":"piter"
                },
                {
                    "name":"luga"
                }
            ]
        }
    ]
}

我有一些不同国家的这种模式的文件，如何从该模式的每个文档中获取所有城市的数组?

i have some documents of such schema for different countries, how can i get an array of ALL cities from each document of this schema?

推荐答案

运行以下聚合管道:

db.collection.aggregate([
    { "$unwind": "$regions" },
    { "$unwind": "$regions.cities" },
    {
        "$group": {
            "_id": null,
            "cities": { "$push": "$regions.cities.name" }
        }
    }
])

样本输出

{
    "result" : [ 
        {
            "_id" : null,
            "cities" : [ 
                "moskva", 
                "tula", 
                "piter", 
                "luga"
            ]
        }
    ],
    "ok" : 1
}

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