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 :

Namespace	Description
System.Data	Contains the basic objects and public classes used for accessing and storing relational data, such as DataSet , DataTable , and DataRelation . Each of these is independent of the type of data source, and independent of the connection type.
System.Data. Common	Contains the base classes used by other public classes in the provider- specific namespaces, in particular those used by the classes in the OleDb , Odbc , OracleClient , and SqlClient namespaces. In general, this namespace is not specifically imported into applications.
System.Data. Odbc	Contains the public classes used to connect to and work with a data source via an ODBC driver, such as OdbcConnection and OdbcCommand . These objects inherit properties, methods , and events from the base classes in the Common namespace.
System.Data. OleDb	Contains the public classes used to connect to and work with a data source via an OLE-DB provider, such as OleDbConnection and OleDbCommand . These objects inherit properties, methods, and events from the base classes in the Common namespace.
System.Data.OracleClient	Contains the public classes used to connect to and work with an Oracle database, such as OracleConnection and OracleCommand . These objects inherit properties, methods, and events from the base classes in the Common namespace, and add Oracle-specific features as well.
System.Data. SqlClient	Contains the public classes used to connect to and work with a data source via the TDS interface of Microsoft SQL Server (only), using classes such as SqlConnection and SqlCommand . These classes provide better performance by removing some of the intermediate layers required by an OLEDB or ODBC provider. These objects inherit properties, methods, and events from the base classes in the Common namespace.
System.Data. SqlServerCe	Contains the public classes used to connect to and work with a data source running under Windows CE. These classes are not used or discussed in this book.
System.Data. SqlTypes	Contains public classes to implement the data types normally found in relational databases such as SQL Server, and which are different to the standard .NET data types. Examples are SqlMoney , SqlDateTime , and SqlBinary . Using these can improve performance and avoid type conversion errors.

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 :

Namespace	Description
System.Xml	Contains the public classes required to create, read, store, write, and manipulate XML documents in line with W3C recommendations. Includes XmlDocument and a series of classes that represent the various types of node in an XML document.
System.Xml. Schema	Contains the public classes required to create, store, and manipulate XML schemas, and the nodes that they contain.
System.Xml. Serialization	Contains public classes that can be used to convert XML documents to other persistence formats, such as SOAP, for streaming to disk or across the wire.
System.Xml. XPath	Contains the public classes required to implement reading, storing, writing, and querying XML documents using a fast custom XPath- based document. Includes XPathDocument , XPathNavigator , and classes that represent XPath expressions.
System.Xml. Xsl	Contains the public classes required to transform XML into other formats using XSL or XSLT stylesheets. The main object is XslTransform .

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.

Important

To use any type of data access code, you must import the appropriate namespace.

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.

Note

For help on using the tools that come with .NET, check out the SDK section .NET Framework Tools from within the Tools and Debugger section. The WinCV utility is described in detail in the subsection Windows Forms Class Viewer ( Wincv.exe ).