C# ASP.NET MVC – How to Mark a Property as Non-Serializable for JSON

[ScriptIgnore] should work for you.

You should use view models. Basically define classes that will contain only the properties that you need to expose and then return those view models from your Web API actions. This way you don't have to worry about polluting your domain models with [JsonIgnore] attributes especially if you don't want those properties to be ignored only for certain actions. In order to simplify the mapping between your domain models and view models you may take a look at AutoMapper.