JsonConverter equivalent in using System.Text.Json

Question

I'm starting to migrate some code I have from Newtonsoft.Json to System.Text.Json in a .net Core 3.0 app.

I migrated the properties from

[JsonProperty("id")] to [JsonPropertyName("id")]

but I have some properties decorated with the JsonConverter attribute as:

[JsonConverter(typeof(DateTimeConverter))] [JsonPropertyName("birth_date")] DateTime BirthDate{ get; set; }

But I cannot find the equivalent of this Newtonsoft converter in System.Text.Json Does someone know how can this be achieved in .net Core 3.0?

Thanks!

Answer 1

System.Text.Json now supports custom type converters in .NET 3.0 preview-7 and above.

You can add converters that match on type, and use the JsonConverter attribute to use a specific converter for a property.

Here's an example to convert between long and string (because javascript doesn't support 64-bit integers).

public class LongToStringConverter : JsonConverter<long> {     public override long Read(ref Utf8JsonReader reader, Type type, JsonSerializerOptions options)     {         if (reader.TokenType == JsonTokenType.String)         {             // try to parse number directly from bytes             ReadOnlySpan<byte> span = reader.HasValueSequence ? reader.ValueSequence.ToArray() : reader.ValueSpan;             if (Utf8Parser.TryParse(span, out long number, out int bytesConsumed) && span.Length == bytesConsumed)                 return number;              // try to parse from a string if the above failed, this covers cases with other escaped/UTF characters             if (Int64.TryParse(reader.GetString(), out number))                 return number;         }          // fallback to default handling         return reader.GetInt64();     }      public override void Write(Utf8JsonWriter writer, long value, JsonSerializerOptions options)     {         writer.WriteStringValue(value.ToString());     } } 

Register the converter by adding it to the Converters list in JsonSerializerOptions

services.AddControllers().AddJsonOptions(options => {     options.JsonSerializerOptions.Converters.Add(new LongToStringConverter()); }); 

Note: The current release doesn't support nullable types yet.

Answer 2

You can find the JsonConverterAttribute in the namespace System.Text.Json.Serialization.

https://docs.microsoft.com/en-us/dotnet/api/system.text.json.serialization.jsonconverterattribute?view=netcore-3.0