Skip to main content

MongoDB error: An error occurred while deserializing the _id field of class … : Cannot deserialize string from BsonType ObjectId.

The last few weeks I’m having fun learning MongoDB. Having some experience with RavenDB, I hoped to re-use most of knowledge when building a MongoDB backend. However I have to conclude that no two No-SQL solutions are alike, so there is still a high learning curve.

I created a sample application, but when I tried to load some objects from the database, I got the following error:

An error occurred while deserializing the _id field of class Product: Cannot deserialize string from BsonType ObjectId.

Let’s have a look at the object I was using; I have a Product class with 2 properties and an ‘_id’ field. The ‘_id’ field is automatically generated by MongoDB for every object you create.

The problem is that behind the scenes MongoDB is storing all objects as BSON documents in the database. The ‘_id’ field isn’t an ordinary string but an ObjectId, a 12-byte BSON type, constructed using:

  • a 4-byte value representing the seconds since the Unix epoch,
  • a 3-byte machine identifier,
  • a 2-byte process id, and
  • a 3-byte counter, starting with a random value.

To fix our error, we have to update our Product class to use the ObjectId type:

Popular posts from this blog

DevToys–A swiss army knife for developers

As a developer there are a lot of small tasks you need to do as part of your coding, debugging and testing activities.  DevToys is an offline windows app that tries to help you with these tasks. Instead of using different websites you get a fully offline experience offering help for a large list of tasks. Many tools are available. Here is the current list: Converters JSON <> YAML Timestamp Number Base Cron Parser Encoders / Decoders HTML URL Base64 Text & Image GZip JWT Decoder Formatters JSON SQL XML Generators Hash (MD5, SHA1, SHA256, SHA512) UUID 1 and 4 Lorem Ipsum Checksum Text Escape / Unescape Inspector & Case Converter Regex Tester Text Comparer XML Validator Markdown Preview Graphic Color B

Help! I accidently enabled HSTS–on localhost

I ran into an issue after accidently enabling HSTS for a website on localhost. This was not an issue for the original website that was running in IIS and had a certificate configured. But when I tried to run an Angular app a little bit later on http://localhost:4200 the browser redirected me immediately to https://localhost . Whoops! That was not what I wanted in this case. To fix it, you need to go the network settings of your browser, there are available at: chrome://net-internals/#hsts edge://net-internals/#hsts brave://net-internals/#hsts Enter ‘localhost’ in the domain textbox under the Delete domain security policies section and hit Delete . That should do the trick…

Azure DevOps/ GitHub emoji

I’m really bad at remembering emoji’s. So here is cheat sheet with all emoji’s that can be used in tools that support the github emoji markdown markup: All credits go to rcaviers who created this list.