Json.Net JsonConstructor attribute alternative for System.Text.Json

Looks like this has now been added as of .NET 5.0 Preview 8:

Announcing .NET 5.0 Preview 8

JsonSerializer improvements in .NET 5

Related issue: JsonSerializer support for immutable classes and structs

Related pull request: Add [JsonConstructor] and support for deserializing with parameterized ctors

Please try this library I wrote as an extension to System.Text.Json to offer polymorphism: https://github.com/dahomey-technologies/Dahomey.Json

Add [JsonConstructor] attribute defined in the namespace Dahomey.Json.Attributes on your class.

public class ObjectWithConstructor
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }

    [JsonConstructor]
    public ObjectWithConstructor(int id, string name)
    {
        Id = id;
        Name = name;
    }
}

Setup json extensions by calling on JsonSerializerOptions the extension method SetupExtensions defined in the namespace Dahomey.Json. Then deserialize your class with the regular Sytem.Text.Json API.

JsonSerializerOptions options = new JsonSerializerOptions();
options.SetupExtensions();

const string json = @"{""Id"":12,""Name"":""foo"",""Age"":13}";
ObjectWithConstructor obj = JsonSerializer.Deserialize<ObjectWithConstructor>(json, options);