Question

In researching how to deserialize a TimeSpan using Newtonsoft s JSON.net I came across code in my current project that did not use Json.net. It used System.Text.Json.JsonSerializer and appeared to not fail on the operation of deserializing the TimeSpan property, as per the unit tests I was running.

Great I thought, .Net Core 3.1 has surpassed the historical issue of deserializing a TimeSpan and all is good. So fired up a test case in the latest version of Linqpad 6 (which uses .NET Core) to verify and to my chagrin it failed.

So the question is, can the TimeSpan be serialized/deserialized using either library (and if so how)… or is my test case below flawed in some respect?

Code

public class Project { public TimeSpan AverageScanTime { get; set; } }

Linqpad C# Code

var newP = new Project() { AverageScanTime = TimeSpan.FromHours(1) };

newP.Dump("New one");

var json = System.Text.Json.JsonSerializer.Serialize(newP);

json.Dump("JSON serialized");

System.Text.Json.JsonSerializer.Deserialize<Project>(json)
                               .Dump("JSON Deserialize");

Deserialize Failure

Answer 1

JsonSerializer for TimeSpan seem will added in Future (removed from .NET 6 milestone). You can trace this issue in Future milestone or this issue.

Before the end of 2022, you need implement JsonTimeSpanConverter on your own. Or you can install Macross.Json.Extensions nuget package and follow the instruction to de/serializer.

At this time, with .NET 6, you can use the build-in Serialize method to serialize and deserialize objects. As below:

System.Text.Json.JsonSerializer.Serialize(
    new { Time = TimeSpan.FromSeconds(100) }
);
// Output:
// {"Time":"00:01:40"}

Answer 2

An addition to the answer from Poy Chang

Swagger (Swashbuckle) also requires a configuration

services.AddSwaggerGen(options =>
{
    options.MapType(typeof(TimeSpan), () => new OpenApiSchema
    {
        Type = "string",
        Example = new OpenApiString("00:00:00")
    });
});

Answer 3

TimeSpanConverter is available in .NET 6.0. So TimeSpan serialization/deserialization will work without custom converters out of the box.

Issue: https://github.com/dotnet/runtime/issues/29932

Implementation: https://github.com/dotnet/runtime/pull/54186

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