How to find and delete duplicate documents in MongoDB

1. Find duplicate documents in MongoDB

db.collection.aggregate([ {$group: { _id: {uniqueField: "$uniqueField"}, uniqueIds: {$addToSet: "$_id"}, count: {$sum: 1} } }, {$match: { count: {"$gt": 1} } } ])

2. Check if index for unique field exists

db.collection.ensureIndex({'uniqueField' : 1}, {unique : true, dropDups : true})

3. Create temp collection with required index

db.temp.createIndex({uniqueField: 1}, {unique: true, dropDups: true})

4. Copy collection with duplicates to temp collection

db.collection.copyTo("temp")

5. Drop collection with duplicates

db.collection.drop()

6. Create new collection with required index and old name

db.collection.createIndex({uniqueField: 1}, {unique: true, dropDups: true})

7. Copy temp collection to new collection with old name

db.temp.copyTo("collection")

8. Drop temp collection =)

db.temp.drop()