Retrieve field value from array of sub document

Question

I have some documents like this:

{
  \"hash\": \"14a076f9f6cecfc58339330eeb492e267f63062f6d5f669c7cdbfecf9eb4de32\",
  \"started_services\": [],
  \"deleted_file         


        

Answer 1

db.key.aggregate((
{ "$match": { 
        "datetime_int": { "$gte": 1451952000 }
        }},
{"$unwind":"$software.adobe.licenses"},
{"$project":{"key":"$software.adobe.licenses.key", "hash":1, "_id":0}}
))

outputs the following :

{ "hash" : "14a076f9f6cecfc58339330eeb492e267f63062f6d5f669c7cdbfecf9eb4de32", "key" : [ "2384723", "23888823" ] }

Answer 2

You can do this with the aggregation framework.

db.repository.aggregate([ 
    { "$match": { 
        "datetime_int": { "$gte": 1451952000 }, 
        "software.adobe.licenses.key" : { "$exists" : true } 
    }}, 
    { "$project": { 
        "hash": 1, 
        "key": { 
            "$map": { 
                "input": "$software.adobe.licenses", 
                "as": "soft", 
                "in": "$$soft.key"
            }
        }
    }}
])

Starting From MongoDB 3.2 you can directly project the sub-document array field.

{ "$project": { "hash": 1, "key": "$software.adobe.licenses.key"}}