How to Customize Enum Values in System.Text.Json?

Customize enumeration values ​​in System.Text.Json

Difficulty: Specifying custom values ​​for enumeration values ​​

In .NET 5 and above, we cannot directly use JsonPropertyName to specify custom values ​​for enumeration values ​​like we can with normal properties. This feature is not available out of the box.

Method 1: Customize JsonConverterFactory (recommended)

To solve this problem, we introduced a JsonConverter factory (JsonEnumMemberStringEnumConverter) that leverages JsonStringEnumConverter and adapted it to use a custom [EnumMember(Value="xxx")] for each enum type annotated with JsonNamingPolicy. For example:

[EnumMember(Value = "Trick-Or-Treat")] // 自定义值
public enum Example { Trick, Treat, TrickOrTreat }

Custom converter registration and usage:

var options = new JsonSerializerOptions
{
    Converters = { new JsonEnumMemberStringEnumConverter() },
    // ...
};
var json = JsonSerializer.Serialize(values, options);

This converter has the following advantages:

• Seamless round trip processing of enums with custom values.
• Preserve custom values ​​when deserializing.
• handles enums with the same value, consistent with JsonStringEnumConverter.
• Supports mutable and immutable enumeration types.

Method 2: Macross.Json.Extensions package

Alternatively, we can use the Macross.Json.Extensions package, which provides a JsonStringEnumMemberConverter that after installation allows us to annotate the enumeration as follows:

[JsonConverter(typeof(System.Text.Json.Serialization.JsonStringEnumMemberConverter))]
public enum Example { Trick, Treat, [EnumMember(Value="Trick-Or-Treat")] TrickOrTreat }

Method Three: Generic Converter Factory with Custom Overrides (Advanced)

If you need finer control, or need to support enums with custom values ​​in versions of .NET earlier than 6.0, you can create a generic converter factory and converter from scratch. This approach is more complex and may require backporting for earlier versions.

Notes

• Enumeration types with [Flags] attributes may require a modified JsonConverter. See the instructions in the response for more details on handling this situation.
• In .NET versions prior to 6.0, JsonStringEnumConverter would ignore its JsonNamingPolicy during deserialization. This issue was fixed in pull request 73348.
• If your enumeration has both [EnumMember] and [JsonPropertyName] attributes, the value of [EnumMember] in the custom converter will take precedence.

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