Part II: Creating the Business Objects

Step 1

Using the File Manager, create a new directory named \MTS. Beneath this new directory, create a directory named SERVER.

Step 2

To start your new Visual Basic ActiveX DLL project, choose References from the Project menu and set references to the Microsoft Remote Data Object 2.0 component and the Microsoft Transaction Server 1.0 Type Library.

Change the properties of Project1 by choosing Project1 Properties from the Project menu. In the Project Properties dialog box, change the name of the project to MTSObject and change the description to MTS Training Exercise Objects. Click OK.

Step 3

In this part of the project, you will use a single class to query the NorthWind data source and return records and you will learn custom marshaling techniques to return data from a lookup table and records from a query.

Change the name of the Class1 class to Query.

Save the project in the \MTS\Server directory.

Step 4

Create a new method in the Query class by choosing Add Procedure from the Tools menu. In the Add Procedure dialog box, set the following attributes:

Name: GetCategories Type: Function Scope: Public 

After inserting the new function, modify it to return a String data type. The complete function should now look like this:

Public Function GetCategories() As String End Function 

The GetCategories method returns a delimited string with all the category names. This technique is a quick way to return lookup table information to a list.

Step 5

Add the following code to the GetCategories method to read the category names from the data source and format the return string:

On Error GoTo GetCategoriesErr     ` Get object context     Dim objContext As MTxAS.ObjectContext     Set objContext = GetObjectContext()          Dim objConnection As RDO.rdoConnection     Dim objResultset As RDO.rdoResultset          ` Make connection.     ` NOTE: Connections made to MTS must     ` be made with the rdDriverNoPrompt option!     Set objConnection = New RDO.rdoConnection     objConnection.Connect = "DSN=NorthWind"     objConnection.EstablishConnection rdDriverNoPrompt, True          ` Run query     Set objResultset = objConnection.OpenResultset _         ("SELECT CategoryName FROM Categories")          ` Build return string     Dim strReturn As String     strReturn = ""          Do While Not objResultset.EOF         strReturn = strReturn & objResultset("CategoryName") & "|"         objResultset.MoveNext     Loop          ` Close connection to allow pooling     objResultset.Close     objConnection.Close     Set objResultset = Nothing     Set objConnection = Nothing     ` Tell MTS we are done     objContext.SetComplete GetCategoriesExit:     GetCategories = strReturn     Exit Function      GetCategoriesErr:     strReturn = Err.Description     ` Tell MTS we failed     objContext.SetAbort     Resume GetCategoriesExit 

Step 6

After the category names are returned to the front end, the user can select a category and see the associated products from the data source for that category. This is accomplished with a method named GetProducts, which returns all the products in an array to the client. The client then uses the array to fill a grid.

Add the GetProduct method by choosing Add Procedure from the Tools menu. In the Add Procedure dialog box, set the following attributes:

Name: GetProducts Type: Function Scope: Public 

Step 7

Change the GetProducts function to accept two arguments and to return a Boolean value that indicates success or failure. The resulting function should look like this:

Public Function GetProducts(strCategory As String, _     ByRef arrProducts As Variant) As Boolean End Function 

Step 8

GetProducts uses the category to search for products and fill an array with results. It also uses Just-In-Time activation to ensure that instances of the Query class are recycled as soon as possible. Add the following code to the GetProducts function to return an array of products to the client:

On Error GoTo GetProductsErr     ' Get object context     Dim objContext As MTxAS.ObjectContext     Set objContext = GetObjectContext()     ' Declare database objects     Dim objConnection As RDO.rdoConnection     Dim objResultset As RDO.rdoResultset          ' Make connection     Set objConnection = New RDO.rdoConnection     objConnection.Connect = "DSN=NorthWind"     objConnection.EstablishConnection rdDriverNoPrompt, True          ' Run query     Dim strSQL As String     strSQL = "SELECT ProductName,CompanyName,UnitPrice "     strSQL = strSQL & "FROM Products,Suppliers,Categories "     strSQL = strSQL & "WHERE Products.SupplierID=Suppliers.SupplierID "     strSQL = strSQL & "AND Products.CategoryID=Categories.CategoryID "     strSQL = strSQL & "AND Categories.CategoryName='" & strCategory & "'"     Set objResultset = objConnection.OpenResultset(strSQL)          ' Build return array     arrProducts = objResultset.GetRows(100)          ' Close connection to allow pooling     objResultset.Close     objConnection.Close     Set objResultset = Nothing     Set objConnection = Nothing          ' Tell MTS we are done     GetProducts = True     objContext.SetComplete      GetProductsExit:     Exit Function      GetProductsErr:     ' Tell MTS we failed     GetProducts = False     objContext.SetAbort     Resume GetProductsExit 

Step 9

Now that the business object is complete, you can compile it by choosing Make MTSObject.dll from the File menu. When the DLL is created, save your work and exit Visual Basic.