By default, the System.Text.Json serializer will convert enumeration members to their numeric values. But suppose we’re interacting with an API that expects named values. To do this, we need to tell the serializer how to convert the enum values into strings. This is the purpose of the EnumStringConverter<T> class.
Let’s assume that the API we’re trying to talk with has a MemberType enumeration with the values free-tier, pro, and enterprise.
We can model this in our code with
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enum MemberType
{
Undefined,
FreeTier,
Pro,
Enterprise
}
but as mentioned, this just renders as numbers in the JSON. Let’s add the converter.
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[JsonConverter(typeof(EnumStringConverter<MemberType>))]
enum MemberType
{
Undefined,
FreeTier,
Pro,
Enterprise
}
This will now render the values as they appear in the C# code, in PascalCase. Still not quite what the API needs. So let’s add some DescriptionAttributes from the System.ComponentModel namespace.
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[JsonConverter(typeof(EnumStringConverter<MemberType>))]
enum MemberType
{
Undefined,
[Description("free-tier")]
FreeTier,
[Description("pro")]
Pro,
[Description("enterprise")]
Enterprise
}
Now the converter will use these strings for the corresponding vauues.
Flag Enums
When an enum has the [Flags] attribute, the converter will output the flag values as a comma-delimited list of string values instead of just a single value. This covers the case where multiple values are “selected.”
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[Flags]
[JsonConverter(typeof(EnumStringConverter<SnowConeColors>))]
enum SnowConeColors
{
[Description("none")]
None = 0,
[Description("red")]
Red = 1,
[Description("orange")]
Orange = 2,
[Description("yellow")]
Yellow = 4,
[Description("green")]
Green = 8,
[Description("blue")]
Blue = 16,
[Description("purple")]
Purple = 32
}
In this case, when we want to serialize the enum value Orange | Green, we’ll get "orange,green" in the serialization.