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8849CH25.qxd  10/16/07  10:51 AM  Page 911

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This interface defines three methods, one of which returns an array of the (yet-to-be-created)

InventoryRecord type. You may recall that the GetInventory() method of InventoryDAL simply

returned a DataTable object, which might make you question why our service’s GetInventory()

method does not do the same. 

While it would work to return a DataTable from a WCF service method, recall that WCF was

built to honor the use of SOA principles, one of which is to program against contracts, not imple-

mentations. Therefore, rather than returning the .NET-specific DataTable type to an external caller,

we will return a custom data contract (InventoryRecord) that will be correctly expressed in the con-

tained WSDL document in an agnostic manner. 

Also note that this interface defines an overloaded method named InsertCar(). The first ver-

sion takes four incoming parameters, while the second version takes an InventoryRecord type as

input. This data contract can be defined as so:

[DataContract]

public class InventoryRecord

{

[DataMember]

public int ID;

[DataMember]

public string Make;

[DataMember]

public string Color;

[DataMember]

public string PetName;

}

If you were to implement this interface as it now stands, build a host, and attempt to call these

methods from a client, you might be surprised to find a runtime exception. The reason has to do

with the fact that one of the requirements of a WSDL description is that each method exposed from

a given endpoint is 

uniquely named. Thus, while method overloading works just fine as far as C# is

concerned, the current web service specifications do not permit two identically named InsertCar()

methods. 

Thankfully, the [OperationContract] attribute supports a named property (Name) that allows

you to specify how the C# method will be represented within a WSDL description. Given this,

update the second version of InsertCar() as so:

public interface IAutoLotService

{

...