Using JSON.net, how do I prevent serializing properties of a derived class, when used in a base class context?

Question

Given a data model:

[DataContract]
public class Parent
{
    [DataMember]
    public IEnumerable<ChildId> Children { get; set; }
}

[DataContract]
public class ChildId
{
    [DataMember]
    public string Id { get; set; }
}

[DataContract]
public class ChildDetail : ChildId
{
    [DataMember]
    public string Name { get; set; }
}

For implementation convenience reasons, there are times when the ChildId objects on the Parent are in fact ChildDetail objects. When I use JSON.net to serialize the Parent, they are written out with all of the ChildDetail properties.

Is there any way to instruct JSON.net (or any other JSON serializer, I'm not far enough into the project to be committed to one) to ignore derived class properties when serializing as a base class?

EDIT: It is important that when I serialize the derived class directly that I'm able to produce all the properties. I only want to inhibit the polymorphism in the Parent object.

Answer 1

I use a custom Contract Resolver to limit which of my properties to serialize. This might point you in the right direction.

e.g.

/// <summary>
/// json.net serializes ALL properties of a class by default
/// this class will tell json.net to only serialize properties if they MATCH 
/// the list of valid columns passed through the querystring to criteria object
/// </summary>
public class CriteriaContractResolver<T> : DefaultContractResolver
{
    List<string> _properties;

    public CriteriaContractResolver(List<string> properties)
    {
        _properties = properties
    }

    protected override IList<JsonProperty> CreateProperties(
        JsonObjectContract contract)
    {
        IList<JsonProperty> filtered = new List<JsonProperty>();

        foreach (JsonProperty p in base.CreateProperties(contract))
            if(_properties.Contains(p.PropertyName)) 
                filtered.Add(p);

        return filtered;
    }
}

In the override IList function, you could use reflection to populate the list with only the parent properties perhaps.

Contract resolver is applied to your json.net serializer. This example is from an asp.net mvc app.

JsonNetResult result = new JsonNetResult();
result.Formatting = Formatting.Indented;
result.SerializerSettings.ContractResolver = 
    new CriteriaContractResolver<T>(Criteria);

Answer 2

I had the exact same problem and looked up how to build the ContractResolver I was actually looking for and that better answer this question. This only serializes the Properties of the Type T you actually want to serialize, but with this example you can also easily build similar approaches:

public class TypeOnlyContractResolver<T> : DefaultContractResolver
{
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        JsonProperty property = base.CreateProperty(member, memberSerialization);
        property.ShouldSerialize = instance => property.DeclaringType == typeof (T);
        return property;
    }
}

Answer 3

Having encountered a similar problem, this is the ContractResolver I came up with:

public class StrictTypeContractResolver : DefaultContractResolver
{
    private readonly Type _targetType;

    public StrictTypeContractResolver( Type targetType ) => _targetType = targetType;

    protected override IList<JsonProperty> CreateProperties( Type type, MemberSerialization memberSerialization )
        => base.CreateProperties
        (
            _targetType.IsAssignableFrom( type ) ? _targetType : type,
            memberSerialization
        );
}

It cuts off only the properties of targetType's descendants, without affecting the properties of its base classes or of other types that targetType's properties might reference. Which, depending on your needs, may or may not be an improvement over the other answers provided here at the time.

Answer 4

Check out the answers in this similar thread, particularly the IgnorableSerializerContractResolver in my answer and the nicer lambda version

Usage:

var jsonResolver = new IgnorableSerializerContractResolver();
// ignore single property
jsonResolver.Ignore(typeof(Company), "WebSites");
// ignore single datatype
jsonResolver.Ignore(typeof(System.Data.Objects.DataClasses.EntityObject));
var jsonSettings = new JsonSerializerSettings() { ReferenceLoopHandling = ReferenceLoopHandling.Ignore, ContractResolver = jsonResolver };

Answer 5

I have not used JSON.Net in particular so not positive this will help you. If JSON.Net derives itself from the .Net serialization system then you should be able to add the [NonSerialized] attribute to your properties you do now wish to be serialized in the base class. When you call the serialize methods on the base class, serialization should then skip those elements.

Answer 6

Haven't compared performance implications, but this is a working solution as well, and works with nested/referenced objects as well.

Derived d = new Derived();           
string jsonStringD = JsonConvert.SerializeObject(d);
Base b = new Base();
JsonConvert.PopulateObject(jsonStringD, b);
string jsonStringB = JsonConvert.SerializeObject(b);