11000 E11000 duplicate key error index: dbName.users.$_id_ dup key: { : ObjectId('5469eb08370fea375383e2d3')}
Problem
I am trying to save an an array of objects into a db using `db.collection.insert` but I am getting this error: [code block] I've tried dropping the database and reinserting but of no use. Also, no document with such id is present in the collection earlier.
Error Output
error index: dbName.users.$_id_ dup key: { : ObjectId('5469eb08370fea375383e2d3') }Unverified for your environment
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1 Fix
Resolve Duplicate Key Error in MongoDB Insert Operation
The error occurs because you are attempting to insert a document with an `_id` that already exists in the collection. Even if you believe the document does not exist, the ObjectId may have been generated previously and is still being referenced in your insert operation.
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- 1
Check for Existing Document
Before inserting, check if a document with the same `_id` already exists in the collection. This can help identify if the duplicate key error is due to an existing document.
javascriptconst existingDoc = await db.collection('users').findOne({ _id: ObjectId('5469eb08370fea375383e2d3') }); - 2
Modify Insert Operation
If the document exists, either update it or remove the `_id` field from the new document to allow MongoDB to generate a new unique `_id` automatically.
javascriptawait db.collection('users').insertOne({ ...newDoc, _id: new ObjectId() }); - 3
Use Bulk Insert with Upsert
If inserting multiple documents, consider using bulk operations with upsert to avoid duplicates. This will insert new documents or update existing ones based on the `_id`.
javascriptconst bulkOps = newDocs.map(doc => ({ updateOne: { filter: { _id: doc._id }, update: { $set: doc }, upsert: true } })); await db.collection('users').bulkWrite(bulkOps); - 4
Verify Insertions
After performing the insert or update operations, verify that the documents have been inserted or updated correctly without any duplicate key errors.
javascriptconst count = await db.collection('users').countDocuments(); console.log('Total documents:', count);
Validation
To confirm the fix worked, check the collection for the expected number of documents and ensure no duplicate key errors are thrown during subsequent insert operations.
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Environment
Submitted by
Alex Chen
2450 rep