ASP.NET Web API uses Json.Net as default formatter, so if your application just only uses JSON as data format, you can use [JsonIgnore] to ignore property for serialization:
public class Foo
{
public int Id { get; set; }
public string Name { get; set; }
[JsonIgnore]
public List<Something> Somethings { get; set; }
}
But, this way does not support XML format. So, in case your application has to support XML format more (or only support XML), instead of using Json.Net, you should use [DataContract] which supports both JSON and XML:
[DataContract]
public class Foo
{
[DataMember]
public int Id { get; set; }
[DataMember]
public string Name { get; set; }
//Ignore by default
public List<Something> Somethings { get; set; }
}
For more understanding, you can read the official article.