How to use $elemMatch on aggregate's projection?

Question

This is my object:

{ \"_id\" : ObjectId(\"53fdcb6796cb9b9aa86f05b9\"), \"list\" : [ \"a\", \"b\" ], \"complist\" : [ { \"a\" : \"a\", \"b\" : \"b\" }, { \"a\         


        

Answer 1

Although the question is old, here is my contribution for November 2017.

I had similar problem and doing two consecutive match operations worked for me. The code below is a subset of my whole code and I changed elements names, so it's not tested. Anyway this should point you in the right direction.

db.collection.aggregate([
    {
        "$match": {
            "_id": "ID1"
        }
    },
    {
        "$unwind": "$sub_collection"
    },
    {
        "$match": {
            "sub_collection.field_I_want_to_match": "value"
        }
    }
])