MongoDB Aggregation: Counting distinct fields

Question

I am trying to write an aggregation to identify accounts that use multiple payment sources. Typical data would be.

{
 account:\"abc\",
 vendor:\"amazon\",
}         


        

Answer 1

I think its better if you execute query like following which will avoid unwind

db.t2.insert({_id:1,account:"abc",vendor:"amazon"});
db.t2.insert({_id:2,account:"abc",vendor:"overstock"});


db.t2.aggregate(
{ $group : { _id : { "account" : "$account", "vendor" : "$vendor" }, number : { $sum : 1 } } },
{ $group : { _id : "$_id.account", number : { $sum : 1 } } }
);

Which will show you following result which is expected.

{ "_id" : "abc", "number" : 2 }