MongoDB Cannot create a namespace in multi-document transaction

Today in this article we shall see how to fix the MongoDB error MongoDB Cannot create a namespace in a multi-document transaction.

Today in this article, we will cover below aspects,

Issue Description

MongoDB gives errors,

MongoDB Cannot create a namespace in multi-document transaction

Resolution

While performing a multi-document operation using MongoDB Driver produces the below error.

This error could be possible using any MongoDb driver like C# MongoDB or node.js or spring boot etc.

I had below sample example where i have defined Transaction scope,

using (var session = await _mongoClient.StartSessionAsync())
            {
                // Begin transaction
                session.StartTransaction();

                //Update the Books Order collection
                var update = Builders<BsonDocument>.Update.Set("OrderId", orderId);
                var updateBuilder = Builders<Library>.Update;
                await orderCollection.UpdateOneAsync(filter, update);

                //Update Books collection for nested array
                await booksCollection.UpdateOneAsync(x => x.userId == inputUserId,
                Builders<Library>.Update.Set("books.$[g].config.$[c].value", inputValue),
                new UpdateOptions
                {
                    ArrayFilters = new List<ArrayFilterDefinition>
                    {
                       new BsonDocumentArrayFilterDefinition<BsonDocument>(new BsonDocument("g.book_name", inputBookName)),
                       new BsonDocumentArrayFilterDefinition<BsonDocument>(new BsonDocument("c.key", key))
                    }
                });

                //All good , let's commit the transaction 
                await session.CommitTransactionAsync();

            }

• After initial trivial, I found one of the collections in was not existing in the MongoDB Database.

• After some research, I found that transaction in mongo currently doesn’t support collection creation within the scope for Mongo Driver version 4.2 and below.

• You need to make sure collections exist before you perform the MongoDB transaction.

• Please verify your collection name is also correct.

After creating the collection and performing the transaction, I was able to resolve the issue.

MongoDB 4.4 and support for collection creation

This is one of the recent features added to MongoDB. With MongoDB version 4.4 and above now support implicit creation of the collection. You can now create an index within the transaction scope.

MongoDB 4.2 and earlier version – No Support for collection creation

For MongoDB 4.2 and earlier versions, creating or dropping a collection or an index, are disallowed for the Transaction operation as they affect the database catalog.

If needed you can perform the collection creation before any transaction.

References:

• MongoDB Distributed Transaction – Guidelines

Did I miss anything else in these resolution steps?

Did the above steps resolve your issue? Please sound off your comments below!

Happy Coding !!

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