Almost everything we do in the software industry relates to data in some way. At some point, all software developers must deal with data, perhaps using a database, text file, spreadsheet, or some other data store. There are many different methods or technologies for using, manipulating, and managing data, and newer methods are continually introduced to enhance existing ones. These methods range from function-based APIs to object-based frameworks and proprietary libraries.
Five years ago, it was common for a simple VB desktop application to access a private Microsoft Access database stored on the local hard disk, but this is no longer a typical scenario. Today’s applications take advantage of distributed-component technologies to exploit scalability and interoperability, thus widening the reach of the application to the enterprise. While ActiveX Data Objects (ADO) served a typical VB application well a few years ago, it might soon fail to meet the increasing demands for better scalability, performance, and interoperability across multiple platforms.
Here’s where ADO.NET comes in. ADO.NET provides huge benefits that allow us to build even better enterprise applications. In this chapter, you will learn the benefits of ADO.NET, the ADO.NET architecture, the main classes in ADO.NET and how they work, and the integration of ADO.NET and XML.
Microsoft ADO.NET’s object model encompasses two distinct groups of classes: content components and managed-provider components . The content components include the DataSet class and other supporting classes such as DataTable, DataRow, DataColumn, and DataRelation. These classes contain the actual content of a data exchange. The managed-provider components assist in data retrievals and updates. Developers can use the connection, command, and data reader objects to directly manipulate data. In more typical scenarios, developers use the DataAdapter class as the conduit to move data between the data store and the content components. The data can be actual rows from a database or any other form of data, such as an XML file or an Excel spreadsheet.
Figure 5-1 shows the high-level architecture of ADO.NET. ADO developers should have no problems understanding connection and command objects. We offer a brief overview then go into more detail in the rest of this chapter.
A data reader is a new object providing fast, forward-only, and read-only access to data. This is similar to an ADO Recordset with server-side, forward-only, and read-only cursor types.
The DataSet class is analogous to a lightweight cache of a particular database from the data store. It allows reading and writing of data and schema in XML, and it is tightly integrated with XmlDataDocument, as you will see later.
The DataAdapter class serves as a higher-level abstraction of the connection and command classes. It enables you to load content from a data store into a DataSet and reconcile DataSet changes back to the data store.