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!

Wouldn't it be easier to use Newtonsoft instead rather than migrating it all over? — DavidG, May 29 '19 at 12:20
That's another question, but I'd like to know if this can be achieved in `System.Text.Json` — Fritjof Berggren, May 29 '19 at 12:21
Not sure the new JSON objects are mature enough to cope with all circumstances right now, but happy to be proven wrong. Making .NET Core 3 use Newtonsoft though, is a one line change I believe. — DavidG, May 29 '19 at 12:23

Mani Gandham · Accepted Answer · 2019-10-28T08:04:14.800

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.

Just for reference: If someone is searching for `StringEnumConverter` in System.Text.Json: `using System.Text.Json.Serialization; [JsonConverter(typeof(JsonStringEnumConverter))]`. Check https://learn.microsoft.com/en-us/dotnet/api/system.text.json.serialization.jsonstringenumconverter?view=netcore-3.0. — FranzHuber23, Oct 08 '19 at 13:26
How do I convert to a custom type? `{x: {foo:1,bar:2,baz:{apple:1,orange:2, juice:[1,2,3,4,5]}}` — boop, Feb 24 '20 at 19:11
@boop You create your type then write a converter that inherits from `JsonConverter` with the read and write logic you need. The documentation has lots of samples that show you how to interact with the API: https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-converters-how-to — Mani Gandham, Feb 25 '20 at 00:01
@FranzHuber23 It does serialize, but it does not respect the `EnumMember` attribute value and thus the Enum name is serialized instead [System.Text.Json: JsonStringEnumConverter ignores its JsonNamingPolicy during deserialization. #31619](https://github.com/dotnet/runtime/issues/31619) — OL., Feb 07 '22 at 13:07

Lars · Answer 2 · 2019-09-26T06:48:46.307

4

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

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

edited Sep 26 '19 at 06:48

answered Sep 25 '19 at 19:01

Lars

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JsonConverter equivalent in using System.Text.Json

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