Using DataContract Proxies In WCF - wcf

Question

So, I have created a couple of WCF services. Each return lists of a certain type of data contract. However, these data contracts have list properties of other data contracts. I am trying to implement lazy-loading of data contract collections.
What I've thought of is to implement a class at the client that inherits from the data contract with collection properties overriden so the setter and getter methods call the service and get the actual collection items.
My question is: How can I make the base channel to return the class that implements the data contract instead of the actual data contract? how can I control what the base channel returns?
My service client looks like this:
public class ServiceClient : BaseClient<IServiceClient>
{
public IList<DataObject> FindAll()
{
// how to control what base.Channel.FindAll return during deserialization.
return base.Channel.FindAll();
}
}
Note that I don't want to do something like this:
public class ServiceClient : BaseClient<IServiceClient>
{
public IList<DataObject> FindAll()
{
var dtos = base.Channel.FindAll();
var dtoProxies = Mapper.Map<DataObject, DataObjectProxy>();
return dtoProxies;
}
}
I want a way so WCF automatically returns a List<DataObject> which elements are actually of type DataObjectProxy.
Any suggestions on how to do this?
Thanks!
EDIT: Sample DataObject class:
[DataContract]
public class DataObject
{
public virtual List<OtherDomainObject> SubItems { get; set; }
}
public class DataObjectProxy : DataObject
{
public override List<OtherDomainObject> SubItems
{
get { // Custom way to retrieve collection... }
set { // Etc.. }
}
}

Answer 1

First, decorate the DataObjectProxy with the [DataContract] attribute, WCF requires explicit contract identifications for all the types - no matter what you gonna do with them later. Then, set [DataMember] on each and every field (property in your case) of the data contract types that you want to expose to the client.
Finally, add [KnownType(typeof(DataObjectProxy))] attribute on the DataObject class. KnownType defines all sub-types of the given base for polymorphic substitutions on the client.
This should work.
[DataContract]
[KnownType(typeof(DataObjectProxy))]
public class DataObject
{
[DataMember]
public virtual List<OtherDomainObject> SubItems { get; set; }
}
[DataContract]
public class DataObjectProxy : DataObject
{
[DataMember]
public override List<OtherDomainObject> SubItems
{
get { // Custom way to retrieve collection... }
set { // Etc.. }
}
}