WCF服务已知类型对象将不返回已知类型的属性

Question

I have created a WCF service and have two particular objects, Contact and Driver. Driver inherits Contact. The Contact object is part of a larger Member object. In the code I have the following:

<DataContract()>
Public Class Contact
    <DataMember()>
    Public Name As String
    <DataMember()>
    Public HomePhone As String
    ... etc.
End Class

<DataContract()>
Public Class Driver
    Inherits Contact
    <DataMember()>
    Public LicenseNum As String
    <DataMember()>
    Public LicenseState As String
    ... etc.
End Class

<DataContract(), KnownType(GetType(Driver))>
Public Class Member
    <DataMember()>
    Public Info As Contact
    <DataMember()>
    Public PrimaryStore As Store
    ... etc.
End Class

Because I have the knowntype on the datacontract line, I can create a Member object with the Info property as a Driver instead of a Contact so I can save their license information.

My problem is that when I create a test project to see the returned data, I can't get the license information when I call the Info property.

Dim svc as New Service.RetrieveService
Dim sMember as Member
Dim memNum as String = "ABC123"
sMember = svc.GetMember(memNum)
Console.WriteLine("LicenseNumber" & sMember.Info...PROBLEM!!!)

sMember.Info only gives me properties belonging to Contact (Name, HomePhone, etc.) and none belonging to Driver (LicenseNum, LicenseState, etc.) How can I access this info?

I have already tried to add ServiceKnownType to my OperationContract as below:

<ServiceContract()>
Public Interface RetrieveMember
    <OperationContract(), ServiceKnownType(GetType(Driver))>
    Function GetMember(ByVal memberNumber as String) As Member
End Interface

but it did not help.

Answer 1

That is because the Member.Info property is defined as the Contact type. That means, even if it references a Driver object, it will still be cast as a Contact object, so only those base members will be visible. This is a problem which is unrelated to WCF. For instance, even removing WCF from the situation, you'd still have the same problem:

Dim m As New Member()
m.Info = New Driver()
Console.WriteLine(m.Contact.LicenseNum)  ' Won't compile!

So, if the Info property is referencing a Driver object, you must cast it to that type before you can access any of the Driver members:

Dim m As Member
' ...
If TypeOf m.Info Is Driver Then
    Dim d As Driver = CType(m.Info, Driver)
    Console.WriteLine(d.LicenseNum)  ' Works fine
End if