Visual Basic

Business Object Browser

After you've created the hierarchy of business objects by having worker objects return factory objects, you can dynamically interrogate this object model and represent it visually. A business object browser is a tremendously powerful tool for programmers to view both the structure and content of the business objects, because it allows the user to drag and drop business objects in the same fashion as the Microsoft Access Relationships editor.

Business object wizard

Creating business objects can be a tedious task. If the data source you're modeling has 200 major entities (easily done for even a medium-size departmental database), that's a lot of business objects you'll have to build. Considering that the factory interface is the same for each business object and that the majority of the properties are derived directly from data fields, much of this process can be automated.

A business object wizard works by analyzing a data entity and then constructing an appropriate factory and worker class. This is not a completely automated process, however! Some code, such as worker objects returning factories, must still be coded manually. Also, any business methods on the worker object obviously have to be coded by hand, but using a business object wizard will save you a lot of time.

TMS uses a business object wizard to develop factory-worker classes based on a SQL Server database. This wizard is written as an add-in for Visual Basic and increases productivity tremendously by creating business objects based on the Shared Recordset implementation. If you need simple business objects, though, you can use the Data Object wizard in Visual Basic 6.0. The mapping of relational database fields to object properties is often referred to as the business object impedance mismatch.

Business object model design guidelines

Keep it simple-avoid circular relationships like the plague. Sometimes this is unavoidable, so make sure you keep a close eye on destroying references, and anticipate that you might have to use explicit destructors on the factory objects to achieve proper teardown. Teardown is the process of manually ensuring that business objects are set to Nothing rather than relying on automatic class dereferencing in Visual Basic. In practice, this means you call an explicit Destroy method to force the release of any internal object references.

Don't just blindly re-create the database structure as an object model; "denormalization" is OK in objects. For example, if you had an Employee table with many associated lookup tables for Department Name, Project Title, and so forth, you should denormalize these into the Employee object; otherwise, you'll be forever looking up Department factory objects to retrieve the Department Name for the employee or the current Project Title. The DAL should be responsible for resolving these foreign keys into the actual values and then transposing them again when update is required. Typically, this is done by a stored procedure in a SQL relational database.

This doesn't mean you won't need a Department factory class, which is still required for retrieving and maintaining the Department data. I'm saying that instead of your Employee class returning the DepartmentID, you should denormalize it so that it returns the Department Name.

MsgBox ocfEmployee.DepartmentName

is better than

MsgBox ocfDepartments(ocfEmployee.DepartmentID).Name

But at the end of the day, the level of denormalization required is up to you to decide. There are no hard and fast rules about denormalization-just try to achieve a manageable, usable number of business objects.