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

You can use sets

db.test.aggregate([
    {$group: { 
      _id: "$account", 
      uniqueVendors: {$addToSet: "$vendor"}
    }},
    {$project: {
      _id: 1, 
      vendorsCount: {$size: "$uniqueVendors"}
    }}
]);