在实体框架4.0中反序列化问题

Question

I am working on an appliction, using Entity Framework 4.0. and WCF.

I am returning list of objects say (Employees)

and the navigational property of that object is say(Departments)

and Department has further a navigational property (Branch)

I am including everything as

Employees.include("Departments.Branch");

Now th issue all those departments whose Branch is same, is set to null(except the first one) upon deserializing on WCF.

I need to use the branch for some binding purposes, kindly guide me how should i get rid of this problem.

This is the screenshot of the entities

Answer 1

It may be that the data is not being loaded before serialisation, but when you debug on the server side, lazy loading causes the data to be loaded.

A couple of things that you could try.

This will force the query to run:

Employees.include("Departments.Branch").ToList();

This will explicitly load the entities:

context.Entry(Employees).Reference(u => u.Departments.Branch).Load();

Answer 2

You could try to use Entity Framework profiler and see whether generated query is having valid data. http://efprof.com/

Answer 3

From MSDN

Windows Communication Foundation (WCF) cannot directly serialize or deserialize proxies because the DataContractSerializer can only serialize and deserialize known types, and proxy types are not known types. When you need to serialize POCO entities, disable proxy creation or use the ProxyDataContractResolver class to serialize proxy objects as the original POCO entities. To disable proxy creation, set the ProxyCreationEnabled property to false.

Beyond that, check if you are using Interoperable Object References ? I would try that as well. Follow the instructions here on how to set it up

Answer 4

On your POCO classes + enumerations and structs (all of them that are serialized), you must have the DataContract attribute with IsReference=true:

[DataContract(Name = "Employee", Namespace = "http://MyNamespace", IsReference=true)]
class Employee
{
    [DataMember(Name="Branch")]
    public Branch _branch = new Branch();
            ... or ...
    [DataMember(Name="Branches")]
    public List<Branch> _branches = new List<Branch>();
}

[DataContract(Name = "Branch", Namespace = "http://MyNamespace", IsReference=true)]
class Branch { ... }

It is the IsReference=true that makes sure that all of the pointers are converted into references during serialization. Also make sure your references have a DataMember attribute.

Answer 5

On the POCO-Classes use [DataContract] for the class, [DataMember] for properties, like Bahri Gungor said. In addition you can write some Methods, which will be called by the Serializer. Check MSDN for: OnDeserialized OnDeserializing , OnSerialized and OnSerializing

In WCF-Service you need to use a Attribute, to declare, where you want to return EF-Proxy-Classes.

[ApplyDataContractResolver]
public POCO_CLASS GetById(int id){
    // your code here...
}

And the ApplyDataContractResolver looks like:

public class ApplyDataContractResolverAttribute : Attribute, IOperationBehavior {
    public ApplyDataContractResolverAttribute() {
    }

    public void AddBindingParameters(OperationDescription description, BindingParameterCollection parameters) {
    }

    public void ApplyClientBehavior(OperationDescription description, System.ServiceModel.Dispatcher.ClientOperation proxy) {
        var dataContractSerializerOperationBehavior = description.Behaviors.Find<DataContractSerializerOperationBehavior>();
        dataContractSerializerOperationBehavior.DataContractResolver = new ProxyDataContractResolver();
    }

    public void ApplyDispatchBehavior(OperationDescription description, System.ServiceModel.Dispatcher.DispatchOperation dispatch) {
        var dataContractSerializerOperationBehavior = description.Behaviors.Find<DataContractSerializerOperationBehavior>();
        dataContractSerializerOperationBehavior.DataContractResolver = new ProxyDataContractResolver();
    }

    public void Validate(OperationDescription description) {
        // Do validation.
    }
}

Background is that the WCF serialise with an DataContractSerializer and EF builds Proxy-Classes to track the changes.

Here a link to MSDN for ProxyDataContractResolver : MSDN

Answer 6

Try to use both .Include() on the query to load related objects and the [Include] attribute in the metadata to allow those related objects to be serialized and sent to the client.

This issue (or at least similar) is discussed here