How to architect DAL for WebService exposure? - web-services

Question

We have a highly specialized DAL which sits over our DB. Our apps need to use this DAL to correctly operate against this DB.
The generated DAL (which sits on some custom base classes) has various 'Rec' classes (Table1Rec, Table2Rec) each of which represents the record structure of a given table.
Here is a sample Pseudo-class...
Public Class SomeTableRec
Private mField1 As String
Private mField1isNull As Boolean
Private mField2 As Integer
Private mField2isNull As Boolean
Public Sub New()
mField1isNull = True
mField2isNull = True
End Sub
Public Property Field1() As String
Get
Return mField1
End Get
Set(ByVal value As String)
mField1 = value
mField1isNull = False
End Set
End Property
Public ReadOnly Property Field1isNull() As Boolean
Get
Return mField1isNull
End Get
End Property
Public Property Field2() As Integer
Get
Return mField2
End Get
Set(ByVal value As Integer)
mField2 = value
mField2isNull = False
End Set
End Property
Public ReadOnly Property Field2isNull() As Boolean
Get
Return mField2isNull
End Get
End Property
End Class
Each class has properties for each of the fields...
Thus I can write...
Dim Rec as New Table1Rec
Table1Rec.Field1 = "SomeString"
Table2Rec.Field2 = 500
Where a field can accept a NULL value, there is an additional property which indicates if the value is currently null.
Thus....
Dim Rec as New Table1Rec
Table1Rec.Field1 = "SomeString"
If Table1Rec.Field1Null then
' This clearly is not true
End If
If Table1Rec.Field2Null then
' This will be true
End If
This works because the constructor of the class sets all NULLproperties to True and the setting of any FieldProperty will cause the equivalent NullProperty to be set to false.
I have recently had the need to expose my DAL over the web through a web service (which I of course intend to secure) and have discovered that while the structure of the 'Rec' class remains intact over the web... All logic is lost..
If someone were to run the previous piece of code remotely they would notice that neither condition would prove true as there is no client side code which sets null to true.
I get the feeling I have architected this all wrong, but cannot see how I should improve it.
What is the correct way to architect this?

Answer 1

Not sure if I fully understand the question, but you can have nullable data types in XML.
So this...
Imports System.Web
Imports System.Web.Services
Imports System.Web.Services.Protocols
<WebService(Namespace:="http://tempuri.org/")> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Public Class Testing
Inherits System.Web.Services.WebService
<WebMethod()> _
Public Function GetObjects() As Generic.List(Of TestObject)
Dim list As New Generic.List(Of TestObject)
list.Add(New TestObject(Nothing, "Empty ID Object"))
list.Add(New TestObject(1, "Full ID Object"))
list.Add(New TestObject(2, Nothing))
Return list
End Function
Public Class TestObject
Public Sub New()
_name = String.Empty
_id = Nothing
End Sub
Public Sub New(ByVal id As Nullable(Of Integer), ByVal name As String)
_name = name
_id = id
End Sub
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Private _id As Nullable(Of Integer)
Public Property ID() As Nullable(Of Integer)
Get
Return _id
End Get
Set(ByVal value As Nullable(Of Integer))
_id = value
End Set
End Property
End Class
End Class
outputs this (with nullable areas)
<?xml version="1.0" encoding="utf-8" ?>
<ArrayOfTestObject xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://tempuri.org/">
<TestObject>
<Name>Empty ID Object</Name>
<ID xsi:nil="true" />
</TestObject>
<TestObject>
<Name>Full ID Object</Name>
<ID>1</ID>
</TestObject>
<TestObject>
<ID>2</ID>
</TestObject>
</ArrayOfTestObject>

Answer 2

Web services are designed to expose operation(methods) & data contracts but not internal implementation logic. This is a "good thing" in the world of service-oriented architecture. The scenario you describe is a remote/distributed object architecture. Web services will not support what you are trying to do. Please see this post for more information.