System.Text.Json easier config for read/deserialize number as string

[hsenasilva]

Hi, I was testing the System.Text.Json deserialization feature and I faced a scenario where double quoted number like "10.00" is parsed to System.Decimal by default on ASP.NET Core apps, and the opposite is not true. Which means that if we send an serialized decimal like 10.00 the default behavior is not the same, and the Converter will throw an exception. I think that could be useful an string implementation like JsonNumberHandling, where could be possible set an option on JsonSerializerOptions to permit parse automatically a number to string without the need to implement a custom converter.

What are your thoughts about this idea? Any side effects on this more permissive approach?

I could send an implementation proposal if you like the idea. o/

[huoyaoyuan]

where could be possible set an option on JsonSerializerOptions to permit parse automatically a number to string

Isn't it covered by JsonNumberHandling.WriteAsString?

[mariussNG]

@huoyaoyuan It is not. This simple test throws an exception:

public class Test
{
    record class MyRecord(string Id);

    [Test]
    public void TestNumberToString()
    {
        const string json = """{"Id": 123}""";

        var jsonOptions = new JsonSerializerOptions { NumberHandling = JsonNumberHandling.WriteAsString };
        var deserialized = JsonSerializer.Deserialize<MyRecord>(json, jsonOptions);

        Console.WriteLine(deserialized);
    }
}

Exception:

System.Text.Json.JsonException : The JSON value could not be converted to Test+MyRecord. Path: $.Id | LineNumber: 0 | BytePositionInLine: 10.
  ----> System.InvalidOperationException : Cannot get the value of a token type 'Number' as a string.

Every other JSON-library I've used accepts this by default, so it is really surprising that System.Text.Json throws an exception, let alone have no simple option to allow it (without implementing a custom converter).

[huoyaoyuan]

This simple test throws an exception:

This is the opposite case, reading JSON numbers as strings. It's not supported by System.Text.Json yet, as https://learn.microsoft.com/dotnet/standard/serialization/system-text-json/migrate-from-newtonsoft?pivots=dotnet-9-0#non-string-values-for-string-properties .