Professional ASP.NET 1.1 [Electronic resources] نسخه متنی

Introducing Data Management in .NET

Having seen why we need a new data access technology, let's look at what .NET actually provides. In this section, you'll get a high-level overview of all of the .NET data management classes, and see how each of the objects fits with the disconnected and structured programming environment that .NET provides. The remainder of this chapter is divided into two sections; relational data management (techniques such as those you used traditional ADO for) and XML data management (for which, traditionally, you would use an XML parser such as MSXML).

System Namespaces for Data Management

The new relational data management classes are in a series of namespaces based on

System.Data within the class library. The combination of the classes from the namespaces in the following table is generally referred to as ADO.NET:

There is also a separate series of namespaces containing the classes used to work with XML rather than relational data. These namespaces are based on

System.Xml :

Importing the Required Namespaces

Pages that use objects from the framework's class libraries must import the namespaces containing all the classes that they explicitly create instances of. Many of the common namespaces are imported by default, but this does not include the data management namespaces.

Importing the System.Data Namespaces

To access relational data, you need at least

System.Data and either

System.Data.OleDb ,

System.Data.SqlClient , or

System.Data.Odbc (depending on the way you're connecting to the data source). In ASP.NET, the

Import page directive is used:

<%@Import Namespace="System.Data" %> 

<%@Import Namespace="System.Data.OleDb" %> 

Or:

<%@Import Namespace="System.Data" %> 

<%@Import Namespace="System.Data.SqlClient" %> 

In Visual Basic .NET code inside a class or module, use the

Imports statement:

Imports System.Data 

Imports System.Data.OleDb 

In C#, use the

using statement:

using System.Data; 

using System.Data.OleDb; 

At times when you need to specifically import other

System.Data namespaces. For example, to create a new instance of a

DataTableMapping class, you need to import the

System.Data.Common namespace, and to use an SQL-specific data type, you need to import the

System.Data.SqlTypes namespace.

Importing the System.Xml Namespaces

To access XML data using the objects in the framework class library, you can often get away with importing just the basic

System.Xml namespace. However, to create an

XPathDocument instance, you have to import the

System.Xml.XPath namespace as well. To use the

XslTransform class to perform server-side transformations of XML documents, you need to import the

System.Xml.Xsl namespace.

The

System.Xml.Schema namespace is usually only required when working with collections of schemas. Most XML validation objects are in

System.Xml , so you can create an

XmlValidatingReader (for example) without referencing the

System.Xml.Schema namespace. But to create a new

SchemaCollection instance, you must import the

System.Xml.Schema namespace.

Type-Not-Found Compilation Errors

If you forget to import any required namespace, you'll get an error as that shown in Figure 8-3. In this case, it indicates that you have forgotten to import the namespace that contains the class for

OleDbConnection . To solve this particular error, you just need to import the namespace

System.Data.OleDb .

Figure 8-3:

To find out which namespace contains a particular class, you can simply look in the .NET SDK Class Library section within the Reference section, or search for the object/class name using the Index or Search feature of the SDK. Alternatively, use the excellent WinCV (Windows Class Viewer) tool that comes with the .NET installation.