Mongodb Duplicate Documents Even After Adding Unique Key

MongoDB Ignoring duplicate documents using unique key in aggregate

You can use $first to get the first element of each group. You can then use $group again to sum by language.

{
  "$group": {
    "_id": {
      "language": "$language",
      "sId": "$sId"
    },
    "count": {
      "$first": {
        "$sum": "$count"
      }
    }
  }
}

https://mongoplayground.net/p/3_RjSt1wtRS

How to remove duplicates based on a key in Mongodb?

This answer is obsolete : the dropDups option was removed in MongoDB 3.0, so a different approach will be required in most cases. For example, you could use aggregation as suggested on: MongoDB duplicate documents even after adding unique key.

If you are certain that the source_references.key identifies duplicate records, you can ensure a unique index with the dropDups:true index creation option in MongoDB 2.6 or older:

db.things.ensureIndex({'source_references.key' : 1}, {unique : true, dropDups : true})

This will keep the first unique document for each source_references.key value, and drop any subsequent documents that would otherwise cause a duplicate key violation.

Important Note: Any documents missing the source_references.key field will be considered as having a null value, so subsequent documents missing the key field will be deleted. You can add the sparse:true index creation option so the index only applies to documents with a source_references.key field.

Obvious caution: Take a backup of your database, and try this in a staging environment first if you are concerned about unintended data loss.

How to stop insertion of Duplicate documents in a mongodb collection

Don't use insert.

Use update with upsert=true. Update will look for the document that matches your query, then it will modify the fields you want and then, you can tell it upsert:True if you want to insert if no document matches your query.

db.collection.update(
   <query>,
   <update>,
  {
    upsert: <boolean>,
     multi: <boolean>,
    writeConcern: <document>
   }
  )

So, for your example, you could use something like this:

db.collection.update(doc, doc, {upsert:true})

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