Allow specific datetime formats in asp.net core app on json deserialization - asp.net-core

Question

I want to allow specific datetime formats in my asp.net core app.
I have this code in Startup.cs on ConfigureServices method:
...
services.AddMvc()
.AddJsonOptions(options =>
{
...
options.SerializerSettings.DateFormatString = "dd/MM/yyyy HH:mm";
})
...
This property allow only one datetime format.
I'm needing something like this (with many datetime formats permitted):
...
services.AddMvc()
.AddJsonOptions(options =>
{
...
options.SerializerSettings.DateFormatString = { "dd/MM/yyyy HH:mm", "dd/MM/yyyy HH:mm:ss", "dd/MM/yyyy", ... };
});
...
Thanks.

Answer 1

This is not possible. Logically, how would the serializer know which format to actually apply? There's no Date type, so a DateTime, even if it no time component is set is still a DateTime and will simply return the time as midnight (00:00:00).
You're struggling here with a basic flaw in API design. An API should not return different types for the same member(s). If time is a component ever, then time should always be present, even if it's zeroed out. Returning different responses puts additional and sometimes impossible burdens on the client.

Answer 2

From https://learn.microsoft.com/en-us/dotnet/standard/datetime/system-text-json-support:
public class DateTimeConverterUsingDateTimeParse : JsonConverter<DateTime>
{
public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
Debug.Assert(typeToConvert == typeof(DateTime));
return DateTime.Parse(reader.GetString());
}
public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
{
writer.WriteStringValue(value.ToString());
}
}
class Program
{
private static void ProcessDateTimeWithCustomConverter()
{
JsonSerializerOptions options = new JsonSerializerOptions();
options.Converters.Add(new DateTimeConverterUsingDateTimeParse());
string testDateTimeStr = "04-10-2008 6:30 AM";
string testDateTimeJson = #"""" + testDateTimeStr + #"""";
DateTime resultDateTime = JsonSerializer.Deserialize<DateTime>(testDateTimeJson, options);
Console.WriteLine(resultDateTime);
string resultDateTimeJson = JsonSerializer.Serialize(DateTime.Parse(testDateTimeStr), options);
Console.WriteLine(Regex.Unescape(resultDateTimeJson));
}
}
This should handle any unambiguous date/time.