MongoDB查询带有嵌入式文档的数组（3个级别）

Question

I had this data on my MongoDB database and I would like to get only the second array about blades.

{
"_id" : ObjectId("..."),
"name" : "Westereems",
"country" : "Netherlands",
"turbines" : [
    {
        "turbine_id" : ObjectId("..."),
        "blades" : [
            {
                "blade_id" : ObjectId("..."),
                "position" : 2,
                "size" : 50,
            }
        ]
    }
]
}

I only want one return with blade_id, position and size. I tried this query and I didn't have the expectable result:

db.collection("windfarms").find({"turbines.blades.blade_id" : ObjectId("...")}, {"turbines.blades.$" : 1, "_id" : 0})

Regards,

Answer 1

You can use this query, it's not an optimal query for large array's items but if you have only above items then you can use it.

you can also go with aggregation to make it more optimal.

db.collection("windfarms").find({"turbines.blades.blade_id" : ObjectId("...")}, {"turbines.blades.blade_id":1,"turbines.blades.position":1,"turbines.blades.size":1,"_id":0})