我可以使用 System.Text.Json 通过私有构造函数反序列化 Json 吗？

想知道是否可以拥有私有构造函数并使用新的 System.Text.Json 序列化器。

public class MyModel
{
    public string Name { get; set; }
    public string Data { get; set; }

    private MyModel() 
    {
        // use me for when deserializing
    }

    public MyModel(string name, string data)
    {
        Name = name;
        Data = data;
    }
}

简单的往返。

var model = new MyModel("doo", "doo");
var json = JsonSerializer.Serialize(model, new JsonSerializerOptions
{
    WriteIndented = true
});

// no to go because of there is no parameterless constructor defined for this object.
var rehydrated = JsonSerializer.Deserialize<MyModel>(json);

.NET 8.0 中的更新

只需添加JsonConstructorAttribute私有构造函数如下：

public class Employee
{
   [JsonConstructor] // This will work from .NET 8.0
   private Employee()
   {
   }

   private Employee(int id, string name)
   {
     Id = id;
     Name = name;
   }

   [JsonInclude]
   public int Id { get; private set; }

   [JsonInclude]
   public string Name { get; private set; }

   public static Employee Create(int id, string name)
   {
     Employee employee = new Employee(id, name);
     return employee;
   }
}

.NET 7.0 中的更新

从 .NET 7.0 开始，可以通过编写自己的 ContractResolver 使用私有无参数构造函数来完成反序列化，如下所示：

public class PrivateConstructorContractResolver : DefaultJsonTypeInfoResolver
{
   public override JsonTypeInfo GetTypeInfo(Type type, JsonSerializerOptions options)
   {
       JsonTypeInfo jsonTypeInfo = base.GetTypeInfo(type, options);

       if (jsonTypeInfo.Kind == JsonTypeInfoKind.Object && jsonTypeInfo.CreateObject is null)
       {
         if (jsonTypeInfo.Type.GetConstructors(BindingFlags.Public | BindingFlags.Instance).Length == 0)
         {
            // The type doesn't have public constructors
            jsonTypeInfo.CreateObject = () => 
                Activator.CreateInstance(jsonTypeInfo.Type, true);
         }
       }

      return jsonTypeInfo;
   }
}

使用方法如下：

private static void Main(string[] args)
{
    JsonSerializerOptions options = new JsonSerializerOptions
    {
       TypeInfoResolver = new PrivateConstructorContractResolver()
    };

    Employee employee = Employee.Create(1, "Tanvir");
    string jsonString = JsonSerializer.Serialize(employee);
    Employee employee1 = JsonSerializer.Deserialize<Employee>(jsonString , options);
}

public class Employee
{
   private Employee()
   {
   }

   private Employee(int id, string name)
   {
     Id = id;
     Name = name;
   }

   [JsonInclude]
   public int Id { get; private set; }

   [JsonInclude]
   public string Name { get; private set; }

   public static Employee Create(int id, string name)
   {
     Employee employee = new Employee(id, name);
     return employee;
   }
}