How to handle stringified numeric enum with System.Text.Json

Question

I have been tasked with trying to migrate an existing application to System.Text.Json in .NET 6. One of the challenges is that I receive json from the front end of the application incorrectly, BUT Newtonsoft is able to handle it.

The first problem I am running into, which is blocking me from finding anything else, is regarding enums.

In the below example, I am getting the numeric value for an enum, however it's being presented as a string from the frontend. Because of this System.Text.Json is unable to parse the value.

I have been playing with custom converters, but so far no luck.

 C#:
 public enum OperationType
 {
 Undefined = 0,
 InnerJoin = 1, 
 }
 
 public class ExampleClass
 {
 public OperationType Operation { get; set; }
 }
 
 Invalid, how do I handle this?
 {
 "operation" : "1"
 }
Valid JSON
 {
 "operation" : 1
 }
 
 Valid JSON
 {
 "operation" : "InnerJoin"
 }

Answer 1

You need to apply a JsonSerializerOptions to the Deserialize method as well as a JsonConverter attribute to the enum declaration, like this:

string json = @"{""operation"" : ""1""}";
JsonSerializerOptions jsonSerializerOptions = new()
{ 
 NumberHandling = JsonNumberHandling.AllowReadingFromString,
 PropertyNameCaseInsensitive = true
};
ExampleClass? example = JsonSerializer.Deserialize<ExampleClass>(json, jsonSerializerOptions);
Debug.WriteLine(example?.Operation);
public class ExampleClass
{
 [JsonConverter(typeof(JsonStringEnumConverter))]
 public OperationType Operation
 {
 get; set;
 }
}

Now you should be able read enum values given as quoted numbers.

• Russ: Thanks @Poul, I had tried each of these individually, but not together. I'm a bit sad given how many enums I need to touch in this project, but that's an implementation detail. Thanks again!
• Yevhen Cherkes: You can configure those settings in startup.cs instead of adding the attribute over all enum fields in DTOs stackoverflow.com/questions/72060614/…