MongoDB query with embedded document in array (3 levels)

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,

Can you show your expected values in question? I am guessing you want something like this { "turbines" : [ { "blades" : [ { "blade_id" : ObjectId("57d28b433366a070b5934650"), "position" : 2, "size" : 50 } ] } ] } — abdulbari
– abdulbari, Commented Sep 19, 2016 at 14:01

abdulbari · Accepted Answer · 2016-09-19 14:14:17Z

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})

answered Sep 19, 2016 at 14:14

abdulbari

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