Find duplicate records in MongoDB

Question

How would I find duplicate fields in a mongo collection.

I\'d like to check if any of the \"name\" fields are duplicates.

{
    \"name\" : \"ksqn291\         


        

Answer 1

The answer anhic gave can be very inefficient if you have a large database and the attribute name is present only in some of the documents.

To improve efficiency you can add a $match to the aggregation.

db.collection.aggregate(
    {"$match": {"name" :{ "$ne" : null } } }, 
    {"$group" : {"_id": "$name", "count": { "$sum": 1 } } },
    {"$match": {"count" : {"$gt": 1} } }, 
    {"$project": {"name" : "$_id", "_id" : 0} }
)