c# - ef4 cause Circular reference in web service

Question

I have a Reason object:

public class Reason
{
    public virtual long Id { get; set; }
    public virtual string Name { get; set; }
    public virtual Company Company {get;set;}
}

I am using entity framework 4 and Company is navigation property to Company.
I also use webservices in order to return data to the client.
I have web method that returns Reasons:

  [WebMethod]
    public Reason[] GetCallReasons()
    {
        IReasonRepository rep =
            ObjectFactory.GetInstance<IReasonRepository>();
        return rep.GetReasonsList().ToArray();
    }

Because of the ef4 I get the following exception for executing the web method:

A circular reference was detected while serializing an object of type 'System.Data.Entity.DynamicProxies.Reason_24A0E4BBE02EE6BC2CF30BB56CFCB670C7D9D96D03D40AF4D174B89C9D3C5537'

The problem accurs because ef4 adds property that can't be serialized:

In order to solve this and eliminate the error, I can disable the navigation property by not making it virtual or by remove the navigation property. But I neet it and want to use the lazy loading feature.

I also can write spesific serializer for Reason but I have many many classes the I used in my web-services and write a serializer for all of them is a lot of work.

How can I solve this exception?..

Answer 1

There are multiple solutions for your problem and they really depend on the type of service you are using and on the type of serialization:

• The clean approach is using DTO (data transfer objects) as @Mikael already suggested. DTO is special object which transfers exactly what you need and nothing more. You can simply create DTOs to not contain circular references and use AutoMapper to map between entities and DTOs and vice versa. +1 for @Mikael because he was the first to mentioned this.

All other approaches are based on tweeking serialization as @Haz suggested:

• WCF and DataContractSerializer: explicitly mark your entities with DataContract[IsReference=true] and all properties with [DataMember] attributes. This will allow you to use circular references. If you are using T4 template to generate entities you must modify it to add these attributes for you.
• WCF and DataContractSerializer: implicit serialization. Mark one of related navigation properties with [IgnoreDataMember] attribute so that property is not serialized.
• XmlSerializer: mark one fo related navigation properties with [XmlIgnore] attribute
• Other serializations: mark one of related navigation properties with [NonSerialized] (+1 for Haz he was the first to mention this) for common serialization or [ScriptIgnore] for some JSON related serialization.