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Default serialization format for TimeSpan

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System.Text.Json added support for TimeSpan in .NET 6 GA, however this change did not include support for source generators. In .NET 6 servicing release 6.0.2, System.Text.Json includes support for source-generator serialization of TimeSpan values. This support changes the default serialization format for TimeSpan values in source generators.

Previous behavior

In .NET 6 GA, source generators serialize TimeSpan values by outputting all public properties of the type, which is the default serialization behavior for objects:

{"days":2,"hours":0,"milliseconds":0,"minutes":0,"seconds":1,"ticks":1728010000000,"totalDays":2.0000115740740743,"totalHours":48.000277777777775,"totalMilliseconds":172801000,"totalMinutes":2880.016666666667,"totalSeconds":172801}

New behavior

In servicing release .NET 6.0.2, source generators serialize TimeSpan values in the following format, which is consistent with the reflection-based serializer format:

"2.00:00:01"

Version introduced

.NET 6.0.2 (servicing release)

Type of breaking change

This change might affect binary compatibility.

Reason for change

System.Text.Json source generation is a new feature, and its serialization behavior should be as consistent as possible with the reflection-based serializer. This change simplifies migration to source generators.

It's unlikely for users to depend on the current TimeSpan serialization format, as it redundantly outputs all public properties of the type (which is the default serialization behavior for objects), and it doesn't roundtrip.

If you do depend on the existing behavior, the recommended course of action is to author a custom converter that outputs the needed properties from TimeSpan:

public class TimeSpanConverter : JsonConverter<TimeSpan>
{
    public void WriteValue(Utf8JsonWriter writer, TimeSpan value, JsonSerializerOptions options)
    {
        writer.WriteStartObject();
        writer.WriteNumber("days", value.Days);
        writer.WriteNumber("hours", value.Hours);
        /* insert any needed properties here */
        writer.WriteEndObject();
    }
}

Affected APIs

See also