MongoDB: How to get distinct list of sub-document field values?

Question

Let\'s say I have the following documents in collection:

{
   \"family\": \"Smith\",
   \"children\": [
        {
            \"child_name\": \"John\"
               


        

Answer 1

with the help aggregation framework:

db.collection.aggregate([{$unwind:'$children'}, {$group:{_id:'$children.child_name'}}])

or more interest ;) with frequency of name:

db.collection.aggregate([{$unwind:'$children'}, {$group:{_id:'$children.child_name', freq:{$sum:1}}}])