Nov 28, 2017

Missing Codecs in MongoDB

When upgrading a project’s Mongo driver from 2.13.0 to 3.4.2, we got the following exception:

org.bson.codecs.configuration.CodecConfigurationException: can't find a codec for class java.math.BigDecimal.

Well it seems that Mongo doesn’t support BigDecimal any longer. There we made our own BigdDecimal Codec. If you search for the “can't find a codec for class” error, you inevitably end up at this StackOverflow entry. However that is about saving nested, custom objects into Mongo. If you search for a while longer you will end up in the Mongo docs that has a simple example with Integer. Seems easy to adopt that for BigDecimal.

But when we did that, we got the same error. it seemed like Mongo was just ignoring our call to the CodecRegistry! The problem was what is described here – we were using a BasicDBObject and not a Document so the Mongo driver wasn’t hitting the CodecRegistry.

I made a Gist overview of how we got it working. The key was adding the Transformer via the static class with this line:  BSON.addEncodingHook(BigDecimal.class, new BigDecimalTransformer()); . We needed both that Transformer and the Codec in the registry for it to work.

I hope that this post can save someone else a few hours/days of head-scratching.

About the Author

Mike Hostetler profile.

Mike Hostetler

Principal Technologist

Mike has almost 20 years of experience in technology. He started in networking and Unix administration, and grew into technical support and QA testing. But he has always done some development on the side and decided a few years ago to pursue it full-time. His history of working with users gives Mike a unique perspective on writing software.

One thought on “Missing Codecs in MongoDB

  1. Joerg says:

    Thanks a lot for this post! Had a similar problem when upgraded Apache Camel to a new version (which also includes upgrade of MongoDB Driver), which broke the software I was working on. Camel community pointed out that this is “wanted-by-design” by the new mongo driver, but that didn’t help getting my code work again.
    Than I Implemented a BigDecimal codec like you suggested in your GIST example, worked like a charm!

    So, indeed, your post saved me a LOT “hours/days of head-scratching” :)!

    1. I’m glad my post helped! The fix is not intuitive.

  2. MarcE says:

    Many thanks! Really good work!

Leave a Reply to Joerg Cancel reply

Your email address will not be published. Required fields are marked *

Related Blog Posts
Google Professional Machine Learning Engineer Exam 2021
Exam Description A Professional Machine Learning Engineer designs, builds, and productionizes ML models to solve business challenges using Google Cloud technologies and knowledge of proven ML models and techniques. The ML Engineer is proficient in all aspects […]
Designing Kubernetes Controllers
There has been some excellent online discussion lately around Kubernetes controllers, highlighted by an excellent Speakerdeck presentation assembled by Tim Hockin. What I’d like to do in this post is explore some of the implications […]
React Server Components
The React Team recently announced new work they are doing on React Server Components, a new way of rendering React components. The goal is to create smaller bundle sizes, speed up render time, and prevent […]
Jolt custom java transform
Jolt is a JSON to JSON transformation library where the transform is defined in JSON. It’s really good at reorganizing the json data and massaging it into the output JSON you need. Sometimes, you just […]