How Can I Handle Unknown Enum Values When Deserializing JSON?

Deserializing JSON with Unknown Enum Values

When parsing JSON data, it's essential to handle scenarios where the provided enum values don't match those defined in your codebase. This commonly occurs when third-party APIs introduce new enum values over time.

Solution: Custom JsonConverter

To tackle this issue, you can create a custom JsonConverter:

class TolerantEnumConverter : JsonConverter
{
    // ... Implementation ...
}

This converter simplifies the deserialization process with the following logic:

• If the JSON value matches an existing enum value (either as a string or integer), it assigns that value.
• For nullable enums, it returns null if the value is missing.
• If the enum contains an "Unknown" value, it sets that value.
• Otherwise, it uses the first enum value.

Sample Usage:

[JsonConverter(typeof(TolerantEnumConverter))]
enum Status { Ready, Set, Go }

string json = @"{ ""status"": ""SomethingElse"" }";

var status = JsonConvert.DeserializeObject<Status>(json); // Returns "Ready"

Nullable Enums and "Unknown" Values:

To handle nullable enums with unknown values, you can add an "Unknown" value to your enum definition. For example:

[JsonConverter(typeof(TolerantEnumConverter))]
enum Color { Red, Yellow, Green, Unknown = 99 }

string colorJson = @"{ ""color"": ""Purple"" }";

var color = JsonConvert.DeserializeObject<Color?>(colorJson); // Returns null

Conclusion:

By utilizing the custom JsonConverter presented here, you can ensure that JSON deserialization proceeds smoothly even when enum values change over time, preventing errors and maintaining data integrity.

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