Application and websites generate too much data even in a single transaction.

How can we handle this huge amount of data efficiently?

Thanks to the NoSQL capabilities of MongoDB, it makes websites scalable and offers superior performance.

However, the MongoDB error code 11000 can happen due to duplicate entries or bad syntax.

At Bobcares, we often get requests from our customers to fix MongoDB error code 11000 as part of our Server Migration Services.

Today, let’s see how our Migration Engineers fix MongoDB error code 11000.

How we fixed MongoDB error code 11000

At Bobcares, where we have more than a decade of expertise in managing servers, we see many customers face problems while managing MongoDB database.

Now let’s see the major reasons for MongoDB errors and how our Support Engineers fix the top errors.

1. Wrong syntax

Recently, one of our customers wanted to recover data from a MySQL database and transform it into JSON for integration into the MongoDB database.

When it was a single insertion it worked fine. But while doing 45000 insertion, it did not work and resulted in the error:

(node:31032) UnhandledPromiseRejectionWarning: WriteError({"code":11000,"index":0,"errmsg":"E11000 duplicate key error collection: meteor.depart index: _id_ dup key: { : ObjectId('5b1527ee6161057938e0aef0') }","op":{"jourExpl
oitation":::::,"_id":"5b1527ee6161057938e0aef0"}})

On checking our MongoDB Experts found that the problem happened due to syntax error.

When using insertMany, we should use the forceServerObjectId flag. Therefore, we suggested the customer to use the following code to solve the problem.

manyInsert.insertMany(dataJsonInsert, { forceServerObjectId: true }); 

This fixed the problem.

2. Duplicate record

Similarly, another customer had an  E11000 duplicate key error index in MongoDB mongoose. The error said

Error creating new user: WriteError({"code":11000,"index":0,"errmsg":"insertDocument :: caused by :: 11000 E11000 duplicate key error index

On checking the schema, we found that the customer renamed the field to username, but didn’t remove the old index. By default, MongoDB will set the value of a non-existent field to null in that case.

If a document does not have a value for the indexed field in a unique index, the index for this document will store a null value.

Due to the unique condition, MongoDB will only allow one document lacking the indexed field. Also, If there is more than one document without a value for the indexed field or is missing the indexed field, the index execution will fail and results in a duplicate key error.

So, our Support Engineers removed the index for the renamed name field and solved the error.

[Need assistance to fix MongoDB error code 11000? We’ll help you.]

Conclusion

In short, the MongoDB error code 11000 may happen when a document does not have a value for the indexed field or due to the wrong syntax used. Today, we saw the various reasons for MongoDB errors and how our Support Engineers fix them.