Question

I have an interface with a property like this:

public interface IFoo {
    // ...

    [JsonIgnore]
    string SecretProperty { get; }

    // ...
}

I want the SecretProperty to be ignored when serializing all implementing classes. But it seems I have to define the JsonIgnore attribute on every implementation of the property. Is there a way to achieve this without having to add the JsonIgnore attribute to every implementation? I didn’t find any serializer setting which helped me.

Answer 1

After a bit of searching, I found this question:

How to inherit the attribute from interface to object when serializing it using JSON.NET

I took the code by Jeff Sternal and added JsonIgnoreAttribute detection, so it looks like this:

class InterfaceContractResolver : DefaultContractResolver
{
    public InterfaceContractResolver() : this(false) { }

    public InterfaceContractResolver(bool shareCache) : base(shareCache) { }

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var property = base.CreateProperty(member, memberSerialization);
        var interfaces = member.DeclaringType.GetInterfaces();
        foreach (var @interface in interfaces)
        {
            foreach (var interfaceProperty in @interface.GetProperties())
            {
                // This is weak: among other things, an implementation 
                // may be deliberately hiding an interface member
                if (interfaceProperty.Name == member.Name && interfaceProperty.MemberType == member.MemberType)
                {
                    if (interfaceProperty.GetCustomAttributes(typeof(JsonIgnoreAttribute), true).Any())
                    {
                        property.Ignored = true;
                        return property;
                    }

                    if (interfaceProperty.GetCustomAttributes(typeof(JsonPropertyAttribute), true).Any())
                    {
                        property.Ignored = false;
                        return property;
                    }
                }
            }
        }

        return property;
    }
}

Using this InterfaceContractResolver in my JsonSerializerSettings, all properties which have a JsonIgnoreAttribute in any interface are ignored, too, even if they have a JsonPropertyAttribute (due to the order of the inner if blocks).