Handling Enum Values in C# with MongoDB: Avoiding Exceptions with Custom Mappers

Learn how to handle C# Enum values stored as strings in MongoDB to prevent exceptions when old values are deleted. Implement a custom deserializer for graceful fallback.
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This video is based on the question https://stackoverflow.com/q/69479487/ asked by the user 'Sugafree' ( https://stackoverflow.com/u/4367493/ ) and on the answer https://stackoverflow.com/a/69495700/ provided by the user 'SJFJ' ( https://stackoverflow.com/u/4172990/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Handling Enum Values in C# with MongoDB: Avoiding Exceptions with Custom Mappers

When working with C# and MongoDB, developers often face common challenges, particularly when storing enums as strings. One significant issue arises when an enum value that was previously used is deleted, leading to exceptions during data retrieval from the database. This post explores a solution to gracefully handle such scenarios by implementing custom mappers.

The Problem

Imagine you have an enum defined as follows:

[[See Video to Reveal this Text or Code Snippet]]

Suppose at some point, you decide to remove the Suv value from this enum. If records in your MongoDB database still reference Suv and you try to retrieve one, this will lead to an exception since the string cannot be mapped back to the current enum definition.

Common Scenario:

You store CarType enum values in MongoDB as strings.

After deleting an enum value (like Suv), fetching a record referencing that value throws an error.

This is where the need for a robust solution comes into play.

The Solution

To resolve this issue, we need to introduce a fallback mechanism that can handle missing enum values gracefully. Here's how we can accomplish this:

1. Define an 'Unknown' Enum Value

First, modify your enum to include an Unknown type that will serve as a fallback:

[[See Video to Reveal this Text or Code Snippet]]

2. Implement a Custom Deserializer

Next, we will create a custom deserializer that will handle the conversion of string values from MongoDB back into the enum. If the value cannot be parsed into a valid enum, it will automatically return CarType.Unknown.

Below is the implementation of the custom deserializer:

[[See Video to Reveal this Text or Code Snippet]]

3. Register the Custom Serializer

Finally, ensure you register this serializer for the property that will be using the enum in your MongoDB document:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following the steps outlined above, you can effectively manage the challenges of using enums with MongoDB. Implementing a custom deserializer not only prevents exceptions when old enum values are deleted but also maintains the integrity of your database operations.

This approach enhances the robustness of your application, ensuring that even if a record refers to a deleted enum, it can still handle it gracefully by falling back to a defined Unknown value.

Make sure to implement and test thoroughly to ensure your application behaves as expected!

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