Using the Visual Studio Object Browser to Explore ADO.NET

To get a better understanding of the ADO.NET namespaces, I suggest that you open Visual Studio and the Object Browser (View | Object Browser), where you'll see a window similar to that shown in Figure 8.2. By using the OB, you can get a better idea of how to address a specific Framework class, get (limited) help on selected objects (via F1), and view the properties, functions, methods, and events of the objects. Don't be alarmed at the sheer volume of classes in the Framework. While I've never counted them, I understand there are over 70,000 of these classes, depending on what's included in the total. Sure, you can gain a complete understanding of ADO.NET development without memorizing these namespacesbut there will be a test on them later.

Figure 8.2. The Visual Studio 2005 Object Browser exploring the Framework Namespaces.

Since this book focuses on SQL Server, I spend considerable time discussing the SqlClient .NET data provider and far less time discussing the OleDb or Odbc providers. Frankly, my previous books on ADO.NET^[2] provide quite a bit of detail on these other providers and how to connect to their data sourcesI won't be revisiting that material here. Once connected, the functionality between providers is very similar, so the concepts you learn when working with SqlClient are similar to those applied to OleDb and Odbc.

^[2] ADO and ADO.NET Examples and Best Practices for Visual Basic Programmers (Apress, 2002) and ADO.NET Examples and Best Practices for C# Programmers (Apress, 2002).

Exploring ADO.NET with a Class Diagram

Visual Studio 2005 includes a new tool called the "Class Diagram" that shows the interrelationships between the base and working classes I code against. If your application builds a number of classes (especially when you're coding complex classes), the Class Diagram tool can make it easier to visualize the classes and their interrelationships, and actually generate your own classes from scratch. If you don't use it for anything else, a Class Diagram can be an effective way to document your classes. I won't have time to teach you how to use the Class Diagram, but I do want to touch on it briefly to give you an idea of its power. To that end, let's create a simple Class Diagram using the Object Browser and a new Class Diagram tool.

1.	Create a new Visual Studio 2005 Windows Application project. Sure, any type of project can contain a Class Diagram. The example creates a Windows Smart Client from the HHGTemplate, but you can use any template you choose. This template is provided with the other examples on the DVD. It simply starts your application off with a user-defined set of references, classes, and commonly used objects.
2.	Right-click on the Project, choose "Add New Item", and choose "Class Diagram" from the "Add New Item" dialogname it "cdExample.cd". This adds a new file to your solution. Visual Studio displays the new Class Diagram design surface in a new windowit instructs you to drag items from the toolbox and visualize existing classes by dragging items from the Class View or Solution Explorer. What it does not tell you is that you can drag classes from the Object Browser as wellthat's what I'm about to do.
3.	Click on the View | Object Browser menu to expose the Object Browser.
4.	Right-click on the "cdExample.cd" tab and choose "Create new vertical tab group"I want to be able to see both the Object Browser and the Class Diagram at the same time. With the Object Browser and Class Diagram side by side, I can easily drag classes from the Object Browser.
5.	Scroll down in the Object Browser until the System.Data.SqlClient namespace is exposed. You should see the same diagram shown in Figure 8.2. Click on the "+" sign to expand the namespace.
6.	Click on the SqlConnection class in the Object Browser. This exposes the list of classes, properties, methods, and events associated with the SqlConnection class.
7.	Right-click on the right pane of the Object Browser and choose "Group by Member Type". This makes it easier to find each type of class within the selected namespace.
8.	Drag the SqlConnection class to the Class Diagram. Left-click on the "SqlConnection" icon in the Object Browser and drag it to the Class Diagram pane. You should see a graphical representation of the SqlConnection class in the Class Diagram, as shown in Figure 8.3. Figure 8.3. Using a Class Diagram to explore the SqlConnection class.
9.	Right-click the "SqlConnection" graphic in the Class Diagram and choose "Show Base Class". This creates a graphical representation of the DbConnection class. If you expose the base class of the DbConnection class, you'll find that it's inherited from the Component class (like all Framework classes).
10.	Right-click on each class you've exposed and choose "Expand" to view the Properties, Methods, and Events implemented by each class. Your Class Diagram should look like Figure 8.4. Figure 8.4. The Visual Studio Class Diagram can expose class properties, methods, and events.

Okay, what can be learned from the diagram in Figure 8.4? Well, notice that the DbConnection class implements several properties and methods that are common to all ADO.NET "connection" classesregardless of the data access provider. Other properties are exposed only on the provider-specific class. For example, SqlConnection implements the PacketSize and StatisticsEnabled properties and the ClearPools method.

The Class Diagram can also be used to show property associations between classes. Let's add a SqlCommand class to the diagram and illustrate this point.

1.	Right-click each class in the Class Diagram and choose "Collapse".
2.	Drag the SqlCommand class from the Object Browser to your Class Diagram. Note that you can reposition any of the graphical representations on the Class Diagram to make them easier to view.
3.	Expand the properties on the SqlCommand class graphic, and right-click the "DbConnection" property. Choose "Show as Association". This connects the SqlCommand class graphic with the graphic for the class that implements DbConnection. Your diagram should look like Figure 8.5 at this pointchoose "Adjust shape width" to expand the property and method names. Figure 8.5. The Class Diagram can be used to show Property/Class associations.

As you can see, a Class Diagram can be a helpful tool to visualize how the ADO.NET classes inherit from one another. This same technique can be used to visualize your own custom classes. Consider that the Class Diagram tool can be used to generate classes as well. I'll let you explore those features on your own. Be back here before the bus leaves for the next stop.

Deciphering the Namespaces

One of the problems you might face when trying to understand ADO.NET seems to be exacerbated by the Object Browserit does not seem to show the "real" object names for many of the objects you're likely to access in code. For example, to address the collection of DataTable objects managed by a DataSet object, you code something like the following Visual Basic .NET code (shown in Figure 8.6) that references the DataSet Tables property.

Figure 8.6. Addressing objects in the ADO.NET namespace is simpler than it seems.

IMHO

I like to hide (for the most part) the underlying .NET Framework classes in the examples I provideI think it makes the code easier to read.

If you have a compelling reason to dig deeper into the SqlClient (or any .NET Framework DLL), you can use Reflector to expose the underlying .NET Framework implementation. While writing this book, I've found it handy to use Reflector to debug more complex .NET issues by studying what ADO.NET is doing when its objects are referenced in code.

Getting a Handle on the Class Names

So, if you started your introduction to ADO.NET by simply drilling into the Object Browser, you might think that you would have to somehow code a reference to the DataTableCollection (as shown in Figure 8.7) when you want to refer to the DataTable objects exposed by a DataSet object.

Figure 8.7. Using the Object Browser to explore the System.Data namespace.

Fortunately, that's not the case, as you'll see when we tour the .NET Framework namespaces. While the DataTableCollection is a class, you don't refer to this class directly. Instead, it's referred to as the DataSet "Tables" property (which is of type DataTable), which points to a specific DataTableCollection instance. Get it? Well, if this is not yet clear, don't panic and sell your Microsoft stock. Visual Studio's Intellisense makes addressing the right object or collection of objects pretty easy. I'll revisit this issue again later in this chapter.

Using Shorthand to Address Classes

Those not familiar with .NET coding might wonder about the first line of Figure 8.8the Visual Basic .NET Imports statement (or the C# using statement). This notation tells the compiler to include this namespace when resolving class names. It does not change the application in any wayand, no, I don't know why these two languages use different terms for the same thing, since they were both created at the same time by (almost) the same company. I use the Imports or using statements to make coding easierat least, to write. Some feel that you should not use the Imports or using statements, as they hide the objects being referenced. This means when you see a class name in code, you won't know the namespace from which it's derived. For example, Figure 8.8 shows how one can reference a SqlConnection class in one of two wayseither directly or indirectly (depending on the Imports statement). You can have as many Imports (or using) statements as needed in your application. Note that the Using statement in Visual Basic .NET means something else entirelyin C#, it serves a dual purpose, but I'll get to those nuances later.

Figure 8.8. Using Imports to specify the namespaces to search when resolving references.

The Visual Studio Object Browser can be a handy tool when you want to explore the classes in selected namespaces or simply locate the namespace containing a class with questionable parentage. For example, if you find an example that contains a class name you can't resolve, you can use the Object Browser to search for all references to the classeven classes you define in your current project. Once you drill down into a specific class and view its functions, methods, properties, and events, you'll see a brief description of the object. In addition, you can press F1 to get object-specific help for the selected item. Of course, that assumes that the help engine is correctly wiredeven after Visual Studio 2005 shipped, the right (or meaningful) help topics don't always materialize when pressing F1.