How hashtable is working in WCF? - wcf

Question

I have a question.
Consider the below
IService1.cs
[ServiceContract]
public interface IService1
{
[OperationContract]
Hashtable GetHashTableCollection();
[OperationContract]
List<A> GetARecords();
}
[DataContract]
public class A
{
[DataMember]
public int MyProperty { get; set; }
[DataMember]
public Hashtable MyTable { get; set; }
}
Service1.cs
public class Service1 : IService1
{
public Hashtable GetHashTableCollection()
{
Hashtable hashtable = new Hashtable();
hashtable.Add("Area", 1000);
hashtable.Add("Perimeter", 55);
hashtable.Add("Mortgage", 540);
return hashtable;
}
public List<A> GetARecords()
{
List<A> Alist = new List<A>();
Alist.Add(new A { MyProperty = 1, MyTable = GetHashTableCollection() });
Alist.Add(new A { MyProperty = 2, MyTable = GetHashTableCollection() });
return Alist;
}
}
And the client Application is as under
private void button1_Click(object sender, EventArgs e)
{
ServiceReference1.Service1Client sc = new ServiceReference1.Service1Client();
var r1 = sc.GetHashTableCollection();
var r2 = sc.GetARecords();
}
It is working fine without any problem. The HashTable has been converted to Dictionary object.
I was under the impression that since HashTable uses IDictionary, so it should fail at compile time(happened in 3.5).
Cannot implicitly convert type 'System.Collections.Generic.Dictionary' to 'System.Collections.Hashtable'
However, it worked. How?
Am I missing any basic concept? Or DataContractSerializer is doing the work? Or something has changed in dot.net 4.0?
What it is and why it is working?

Answer 1

It's based on IDictionary. WCF treats IDictionary as a Dictionary<object, object> and it's exposed as such on the WSDL. You could have a custom class which implemented IDictionary, and the behavior would be the same. For example, if you run either of the projects below, and use svcutil or Add Service Reference to generate a proxy to the service, where you had an IDictionary type, you'll get a Dictionary<object, object> in the client instead.
public class StackOverflow_15471185
{
[ServiceContract]
public interface IService1
{
[OperationContract]
Hashtable GetHashTableCollection();
[OperationContract]
List<A> GetARecords();
}
[DataContract]
public class A
{
[DataMember]
public int MyProperty { get; set; }
[DataMember]
public Hashtable MyTable { get; set; }
}
public class Service : IService1
{
public Hashtable GetHashTableCollection()
{
Hashtable hashtable = new Hashtable();
hashtable.Add("Area", 1000);
hashtable.Add("Perimeter", 55);
hashtable.Add("Mortgage", 540);
return hashtable;
}
public List<A> GetARecords()
{
List<A> Alist = new List<A>();
Alist.Add(new A { MyProperty = 1, MyTable = GetHashTableCollection() });
Alist.Add(new A { MyProperty = 2, MyTable = GetHashTableCollection() });
return Alist;
}
}
public static void Test()
{
string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
ServiceHost host = new ServiceHost(typeof(Service), new Uri(baseAddress));
host.AddServiceEndpoint(typeof(IService1), new BasicHttpBinding(), "");
host.Description.Behaviors.Add(new ServiceMetadataBehavior { HttpGetEnabled = true });
host.Open();
Console.WriteLine("Host opened");
var factory = new ChannelFactory<IService1>(new BasicHttpBinding(), new EndpointAddress(baseAddress));
var proxy = factory.CreateChannel();
Console.WriteLine(proxy.GetHashTableCollection());
((IClientChannel)proxy).Close();
factory.Close();
Console.Write("Press ENTER to close the host");
Console.ReadLine();
host.Close();
}
}
public class StackOverflow_15471185_b
{
[ServiceContract]
public interface IService1
{
[OperationContract]
MyDic GetHashTableCollection();
[OperationContract]
List<A> GetARecords();
}
public class MyDic : IDictionary
{
public IDictionary dic = new Hashtable();
public void Add(object key, object value)
{
dic.Add(key, value);
}
public void Clear()
{
dic.Clear();
}
public bool Contains(object key)
{
return dic.Contains(key);
}
public IDictionaryEnumerator GetEnumerator()
{
return dic.GetEnumerator();
}
public bool IsFixedSize
{
get { return dic.IsFixedSize; }
}
public bool IsReadOnly
{
get { return dic.IsReadOnly; }
}
public ICollection Keys
{
get { return dic.Keys; }
}
public void Remove(object key)
{
dic.Remove(key);
}
public ICollection Values
{
get { return dic.Values; }
}
public object this[object key]
{
get
{
return dic[key];
}
set
{
dic[key] = value;
}
}
public void CopyTo(Array array, int index)
{
dic.CopyTo(array, index);
}
public int Count
{
get { return dic.Count; }
}
public bool IsSynchronized
{
get { return dic.IsSynchronized; }
}
public object SyncRoot
{
get { return dic.SyncRoot; }
}
IEnumerator IEnumerable.GetEnumerator()
{
return ((IEnumerable)dic).GetEnumerator();
}
}
[DataContract]
public class A
{
[DataMember]
public int MyProperty { get; set; }
[DataMember]
public MyDic MyTable { get; set; }
}
public class Service : IService1
{
public MyDic GetHashTableCollection()
{
MyDic hashtable = new MyDic();
hashtable.Add("Area", 1000);
hashtable.Add("Perimeter", 55);
hashtable.Add("Mortgage", 540);
return hashtable;
}
public List<A> GetARecords()
{
List<A> Alist = new List<A>();
Alist.Add(new A { MyProperty = 1, MyTable = GetHashTableCollection() });
Alist.Add(new A { MyProperty = 2, MyTable = GetHashTableCollection() });
return Alist;
}
}
public static void Test()
{
string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
ServiceHost host = new ServiceHost(typeof(Service), new Uri(baseAddress));
host.AddServiceEndpoint(typeof(IService1), new BasicHttpBinding(), "");
host.Description.Behaviors.Add(new ServiceMetadataBehavior { HttpGetEnabled = true });
host.Open();
Console.WriteLine("Host opened");
var factory = new ChannelFactory<IService1>(new BasicHttpBinding(), new EndpointAddress(baseAddress));
var proxy = factory.CreateChannel();
Console.WriteLine(proxy.GetHashTableCollection());
((IClientChannel)proxy).Close();
factory.Close();
Console.Write("Press ENTER to close the host");
Console.ReadLine();
host.Close();
}
}