Question

I am trying to write a C# restful web service which returns the customer name when account number is passed as a parameter.

I have a customer class:

public class Customer_T
{
    public string CustName { get; set; }
}

An interface class:

[ServiceContract(Namespace = "", Name = "CustomerInfoService")]
public interface CustomerInfo_I
{
    [OperationContract]
    Customer_T CustName(string accountno);
}

*Another class called CustomerInfo which implements the CustomerInfo_I interface:*

[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]
public class CustomerInfo : CustomerInfo_I
{
    [WebInvoke(Method = "GET", UriTemplate = "customer/{accountno}", ResponseFormat = WebMessageFormat.Json)]
    public Customer_T CustName(string accountno)
    {
        string custName = "";
        CustNameByAccountNo custdb = new CustNameByAccountNo();
        custName = custdb.getCustName(accountno).ToString();
        if (custName.Equals("") == false)
        {
            return new Customer_T { CustName = custName };
        }
        else
        {
            return null; //This is where I want to change
        }
    }
}

Instead of returning null, I would like to return a string “InvalidAccNo”.
I did try it, but it gave me an error.

Cannot implicitly convert type 'string' to 'CustomerInfo.Service.Customer_T'

Answer 1

You won’t be able to return a string since your return type is defined as a Customer_T. One option you might want to consider is to take a look at fault handling inside of WCF to return a fault to a user rather than repurposing a single object. Throwing the fault can be used in indicate that an invalid account number was specified.

[ServiceContract(Namespace = "", Name = "CustomerInfoService")]
public interface CustomerInfo_I
{
    [OperationContract]
    [FaultContract(typeof(string))]
    Customer_T CustName(string accountno);
}

http://msdn.microsoft.com/en-us/library/ms733721.aspx

Also, your Customer class, you should mark the class with the DataContract attribute and your data members with DataMember in order to return complex types.

[DataContract]
public class Customer_T
{
    [DataMember]
    public string CustName { get; set; }
}