Order of fields when serializing the derived class in JSON.NET

Question

Consider these two classes:

public Class Base {
    public string Id {get; set;}
    public string Name {get; set;}
    public string LastName {get; set;}
}

And the derived class:

public Class Derived : Base {
    public string Address {get; set;}
    public DateTime DateOfBirth {get; set;}
}

When serializing the Derived class using Json.Net:

Derived record = new Derived record(); {// Initialize here...}
JsonConvert.SerializeObject(record);

By default, the properties of the Derived class appear first:

{ 
  "address": "test", 
  "date_of_birth" : "10/10/10",
  "id" : 007,
  "name" : "test name",
  "last_name": "test last name"
 }

What I need:

{ 
  "id" : 007,
  "name" : "test name",
  "last_name": "test last name"
  "address": "test", 
  "date_of_birth" : "10/10/10",      
 }

Question

Is it possible to have the base class properties come first, when serializing the derived class (without using [JsonProperty(Order=)] for each property of both classes)?

Answer 1

According to the JSON standard, a JSON object is an unordered set of name/value pairs. So my recommendation would be to not worry about property order. Nevertheless you can get the order you want by creating your own ContractResolver inheriting from one of the standard contract resolvers, and then overriding CreateProperties:

public class BaseFirstContractResolver : DefaultContractResolver
{
    protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization) =>
        base.CreateProperties(type, memberSerialization)
            ?.OrderBy(p => p.DeclaringType.BaseTypesAndSelf().Count()).ToList();
}

public static class TypeExtensions
{
    public static IEnumerable<Type> BaseTypesAndSelf(this Type type)
    {
        while (type != null)
        {
            yield return type;
            type = type.BaseType;
        }
    }
}

And then use it like:

// Cache an instance of the resolver for performance
static IContractResolver baseFirstResolver = new BaseFirstContractResolver { /* Set any required properties here e.g.  NamingStrategy = new CamelCaseNamingStrategy() */ };

// And use the cached instance when serializing and deserializing
var settings = new JsonSerializerSettings 
{ 
    ContractResolver = baseFirstResolver, 
    // Add your other settings here.
    TypeNameHandling = TypeNameHandling.Objects 
};
var json = JsonConvert.SerializeObject(derived, typeof(Base), Formatting.Indented, settings);

Notes:

• This approach works especially well with multi-level type hierarchies as it automates correct ordering of properties from all levels in the hierarchy.

• Newtonsoft recommends caching instances of contract resolvers for best performance.

Demo fiddle here.