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Chapter 3 Introduction to ADO.NET

In this chapter, you will:

 Learn the basic classes in ADO.NET and its

architecture Learn the different ADO.NET Data Providers Learn about the Connection and Command components

Later Learn about the Parameters collection component Learn about the DataReader components.

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3.2    Overview of the ADO.NET

ADO.NET is a set of classes provides a rich set of components for creating distributed, data-sharing applications.

ADO.NET is an integral part of the Microsoft .NET Framework. All ADO.NET classes are located at the System.Data

namespace . When compiling code that uses the System.Data namespace,

reference both System.Data.dll and System.Xml.dll.

Basically speaking, ADO.NET provides a set of classes to support you to develop database applications and enable you to connect to a data source to retrieve, manipulate and update data with your database.

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Chapter 3 Introduction to ADO.NET

The classes provided by ADO.NET are core to develop a professional data-driven application and they can be divided into the following three major components:

Data Provider DataSet DataTable These three components are located at the different

namespaces. The DataSet and the DataTable classes are located at the System.Data namespace. The classes of the Data Provider are located at the different namespaces based on the types of the Data Providers.

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Chapter 3 Introduction to ADO.NET

Data Provider contains four classes: Connection, Command, DataAdapter and DataReader. These four classes can be used to perform the different functionalities to help you to:

Set a connection between your project and the data source using the Connection object

Execute data queries to retrieve, manipulate and update data using the Command object

Move the data between your DataSet and your database using the DataAdapter object

Perform data queries from the database (read-only) using the DataReader object

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Chapter 3 Introduction to ADO.NET The DataSet class can be considered as a table container

and it can contain multiple data tables. These data tables are only a mapping to those real data tables in your database. But these data tables can also be used separately without connecting to the DataSet. In this case, each data table can be considered as a DataTable object.

The DataSet and DataTable classes have no direct relationship with the Data Provider class; therefore they are often called Data Provider-independent components.

Four classes such as Connection, Command, DataAdapter and DataReader that belong to Data Provider is often called Data Provider-dependent components.

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3.3  The Architecture of ADO.NET

The ADO.NET architecture can be divided into two logical pieces:

command execution and caching.

Command execution requires features like connectivity, execution, and reading of results. These features are enabled with ADO.NET Data Providers.

Caching of results is handled by the DataSet.

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The Architecture of the ADO.NET

Figure 3-1. A typical architecture of the ADO.NET

Connection

Command

DataReader

DataSet Data Provider

Database

Transaction

Parameters

DataAdapter

DeleteCommand

SelectCommand

InsertCommand

UpdateCommand

DataTableCollection

ConstraintCollection

DataTable

DataRowCollection

DataColumnCollection

DataRelationCollection

Your Application

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The Architecture of the ADO.NET - 2

Figure 3-2. Another architecture of the ADO.NET

Connection

DataAdapter

DataReader

Data Provider

Database

Transaction Command

ExecuteReader

Parameters

ExecuteNonQuery

ExecuteScalar

DataSet DataRelationCollection

ConstraintCollection

DataTable

DataRowCollection

DataColumnCollection

Your Application

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3.4 The Components of ADO.NET

3.4.1 The Data Provider

The Data Provider can also be called a data driver and it can be used as a major component for your data-driven applications. The functionalities of the Data Provider, as its name means, are to:

Connect your data source with your applications Execute different methods to perform the associated data

query and data accessing operations between your data source and your applications

Disconnect the data source when the data operations are done

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3.4.1 The Data Provider The Data Provider is physically composed of a binary library

file and this library is in the DLL file format. Sometimes this DLL file depends on other DLL files, so in fact a Data Provider can be made up of several DLL files. Based on the different kinds of databases, Data Provider can have several versions and each version is matched to each kind of database. The popular versions of the Data Provider are:

Open DataBase Connectivity (Odbc) Data Provider (ODBC.NET)

Object Linking and Embeding DataBase (OleDb) Data Provider (OLEDB.NET)

SQL Server (Sql) Data Provider (SQL Server.NET) Oracle (Oracle) Data Provider (Oracle.NET)

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3.4.1 The Data Provider

The different data providers are located at the different namespaces, and these namespaces hold the various data classes that you must import into your code in order to use those classes in your project.

Table 3-1 lists the most popular namespaces used by the different data providers and used by the DataSet and the DataTable.

Table 3-1. Namespaces for different Data Providers, DataSet and DataTable Namespaces Descriptions System.Data Holds the DataSet and DataTable classes System.Data.OleDb

Holds the class collection used to access an OLEDB data source System.Data.SqlClient

Holds the classes used to access an SQL Server 7.0 data source or later

System.Data.Odbc

Holds the class collection used to access an ODBC data source System.Data.OracleClient

Holds the classes used to access an Oracle data source

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3.4.1.1   The ODBC Data Provider

The ODBC.NET supports the following Data Providers:

SQL Server Microsoft ODBC for Oracle Microsoft Access Driver (*.mdb)

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3.4.1.2   The OLEDB Data Provider

The OLE DB.NET data access technique supports the following Data Providers:

Microsoft Access SQL Server (7.0 or later) Oracle (9i or later)

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3.4.1.3   The SQL Server Data Provider

This Data Provider provides access to a SQL Server version 7.0 or later database using its own internal protocol. The functionality of the data provider is designed to be similar to that of the .NET Framework data providers for OLE DB, ODBC, and Oracle. All classes related to this Data Provider are defined in a DLL file and is located at the System.Data.SqlClient namespace. Although Microsoft provides different Data Providers to access the data in SQL Server database, such as the ODBC and OLE DB, for the sake of optimal data operations, it is highly recommended to use this Data Provider to access the data in an SQL Server data source.

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This Data Provider is an add-on component to the .NET Framework that provides access to the Oracle database. All classes related to this Data Provider are located in the System.Data.OracleClient namespace. This provider relies upon Oracle Client Interfaces provided by the Oracle Client Software. You need to install the Oracle Client software on your computer to use this Data Provider.

Microsoft provides multiple ways to access the data stored in an Oracle database, such as Microsoft ODBC for Oracle and OLE DB, you should use this Data Provider to access the data in an Oracle data source since this one provides the most efficient way to access the Oracle database.

3.4.1.4   The Oracle Data Provider

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Data Provider contains four sub-classes and the Connection component is one of them. This class provides a connection between your applications and the database you selected to connect to your project. To use this class to setup a connection between your application and the desired database, you need first to create an instance or an object based on this class.

The Connection object you want to use depends on the type

of the data source you selected. Data Provider provides four different Connection classes and each one is matched to one different database.

3.4.2   The Connection Class

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Table 3-3 lists these popular Connection classes used for the different data sources:

3.4.2   The Connection Class

Table 3-3. The Connection classes and databases Connection Class Associated Database OdbcConnection ODBC Data Source OleDbConnection OLE DB Database SqlConnection SQL Server Database OracleConnection Oracle Database

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3.4.2   The Connection Class

The connection string is a property of the Connection class and it provides all necessary information to connect to your data source. Regularly this connection string contains a quite few parameters to define a connection, but only five of them are popularly utilized for most data-driven applications:

Provider Data Source Database User ID Password

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The Provider parameter

Specifies the driver that the connection class uses to communicate with the database.

The most common drivers are: Microsoft.Jet.OLEDB.4.0 for Access SQLOLEDB for SQL Server MSDAORA for Oracle

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is used to specify the server name of the computer on which the database is running.

When connecting to an Access database, this specifies the path and database name.

The Data Source parameter

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The Database parameter

Is self-explanatory and specifies the database name where your data resides

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User ID and Password parameters

They are used to specify your database login credentials

The User ID and Password defined in the database, not your Windows login credentials.

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A typical data connection instance with a general connection string can be expressed by the following codes:

 Connection = New xxxConnection(“Provider = MyProvider;” & _ “Data Source = MyServer;” & _

“Database = MyDatabase;” & _“User ID = MyUserID;” & _“Password = MyPassWord;”)

where xxx should be replaced by the selected Data Provider in

your real application, such as OleDb, Sql or Oracle. You need to use the real parameter values implemented in your applications to replace those nominal values such as MyServer, MyDatabase, MyUserID and MyPassWord in your application.

3.4.2   The Connection Class

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The Provider parameter indicates the database driver you selected. If you installed a local SQL server and client such as the SQL Server 2005 Express on your computer, the Provider should be localhost. If you are using a remote SQL Server instance, you need to use that remote server’s network name. If you are using the default named instance of SQLX on your computer, you need to use .\SQLEXPRESS as the value for your Provider parameter. For the Oracle server database, you do not need to use this parameter.

The Data Source parameter indicates the name of the network computer

on which your SQL server or Oracle server is installed and running.

The Database parameter indicates your database name.

The User ID and Password parameters are used for the security issue for your database. In most cases, the default Windows NT Security Authentication is utilized.

3.4.2   The Connection Class

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Some typical Connection instances are listed below: OLE DB Data Provider for Microsoft Access Database 2003 Connection = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;" &

_ "Data Source=C:\database\CSE_DEPT.mdb;" & _

"User ID=MyUserID;" & _"Password=MyPassWord;")

OLE DB Data Provider for SQL SERVER Connection = New OleDbConnection("Provider=SQLOLEDB.1;" & _ "Data Source=MyComputerName\SQLEXPRESS;" & _

"Database =MyDatabseName;" & _"User ID=MyUserID;" & _"Password=MyPassWord;")

 

3.4.2   The Connection Class

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Some typical Connection instances are listed below: 

SQL Server Data Provider for SQL Server Database Connection = New SqlConnection("Server=localhost;" + _ "Data Source=Susan\SQLEXPRESS;" + _ "Database=CSE_DEPT;" + _

"Integrated Security=SSPI")  Oracle Data Provider for Oracle DatabaseConnection = New OracleConnection("Data Source=XE;" + _ "User ID=system;" + _ "Password=reback")

3.4.2   The Connection Class

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To create a real connection between your database and your applications, the Open() method of the Connection class is called and it is used to open a connection to a data source with the property settings specified by the connection string.

An example of opening an OLEDB connection

3.4.2.1   The Open() Method of the Connection Class

Figure 3-3. An example coding of the opening a connection

Dim strConnectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0;" & _ "Data Source=C:\database\CSE_DEPT.mdb;" accConnection = New OleDbConnection(strConnectionString) Try accConnection.Open() Catch OleDbExceptionErr As OleDbException MessageBox.Show(OleDbExceptionErr.Message, "Access Error") Catch InvalidOperationExceptionErr As InvalidOperationException MessageBox.Show(InvalidOperationExceptionErr.Message, "Access Error") End Try If accConnection.State <> ConnectionState.Open Then MessageBox.Show("Database Connection is Failed") Exit Sub End If

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The Close() method is a partner of the Open() method and it is used to close a connection between your database and your applications when you finished your data operations to the data source. You should close any connection object you connected to your data source after you finished the data access to that data source, otherwise a possible error may be encountered when you try re-open that connection in the next time as you run your project.

Unlike the Open() method, which is a key to your data access and operation to your data source, the Close() method does not throw any exceptions when you try to close a connection that has already been closed. So you do not need to use a Try….Catch block to catch any error for this method.

3.4.2.2   The Close() Method of the Connection Class

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The Dispose() method of the Connection class is an overloaded method and it is used to releases the resources used by the Connection object. You need to call this method after the Close() method is executed to perform a cleanup job to release all resources used by the Connection object during your data access and operations to your data source.

After the Close() and Dispose() methods executed, you can release your reference to the Connection instance by setting it to Nothing. A piece of example code is shown in Figure 3-4.

3.4.2.3   The Dispose() Method of the Connection Class

Figure 3-4. An example coding for the cleanup of resources

' clean up the objects used accConnection.Close() accConnection.Dispose() accConnection = Nothing

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Command objects are used to execute commands against your database such as a data query, an action query, and even a stored procedure. In fact, all data accesses and data operations between your data source and your applications are achieved by executing the Command object with a set of parameters.

Command class can be divided into the different categories and these categories are based on the different Data Providers. For the popular Data Providers, such as OLE DB, ODBC, SQL Server and Oracle, each one has its own Command class. Each Command class is identified by the different prefix such as OleDbCommand, OdbcCommand, SqlCommand and OracleCommand. Although these different Command objects belong to the different Data Providers, they have the similar properties and methods, and they are equivalent in functionalities.

3.4.3 The Command and the Parameter Classes

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3.4.3.1   The Properties of the Command Class

The Command class contains more than 10 properties, but only four of them are used popularly in most applications:

Connection property CommandType property CommandText property Parameters property

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3.4.3.1   The Properties of the Command Class

Connection property holds a valid Connection object, and the Command object can be executed to access the connected database based on this Connection object.

CommandType property indicates what kind of command that

is stored in the CommandText property should be executed.

CommandText property contains a complete SQL statement if the value of the CommandType property is Text.

Parameters property holds a collection of the Parameter objects. You must first create and initialize a Parameter object before you can add that object to the Parameters collection for a Command object.

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3.4.3.5   The Constructor of the Command Class

The constructor of the Command class is an overloaded method and it has multiple protocols. Four popular protocols are listed in Figure 3-8 (an SQL Server Data Provider is used as an example).

Figure 3-8. Three popular protocols of the constructor of the Command class

Dim sqlCommand As New SqlCommand() Dim sqlCommand As New SqlCommand(connString) Dim sqlCommand As New SqlCommand(connString, SqlConnection) Dim sqlCommand As New SqlCommand(connString, SqlConnection, SqlTransaction)

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3.4.3.6   The Methods of the Command Class

The actual execution of a Command object is to run one of methods of the Command class to perform the associated data queries or data actions. Four popular methods are widely utilized for most data-driven applications and Table 3-6 lists these methods.

Table 3-6. Methods of the Command class Method Name Functionality ExecuteReader Executes commands that return rows, such

as a SQL SELECT statement. The returned rows are located in an OdbcDataReader, an OleDbDataReader, a SqlDataReader or an OracleDataReader, depending on which Data Provider you are using.

ExecuteScalar Retrieves a single value from the database. ExecuteNonQuery Executes a non-query command such as

SQL INSERT, DELETE, UPDATE, and SET statements.

ExecuteXmlReader (SqlCommand only) Similar to the ExecuteReader method, but the returned rows must be expressed using XML. This method is only available for the SQL Server Data Provider.

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3.4.3.2   The Constructors and Properties of the Parameter Class

The Parameter class has four popular constructors, which are shown in Figure 3-5 (an SQL Server Data Provider is used as an example).

Dim sqlParameter As New SqlParameter() Dim sqlParameter As New SqlParameter(ParamName, objValue) Dim sqlParameter As New SqlParameter(ParamName, sqlDbType) Dim sqlParameter As New SqlParameter( ParamName, sqlDbType, intSize)

Table 3-4. The data types and the associated Data Provider Data Type Associated Data Provider OdbcType ODBC Data Provider OleDbType OLE DB Provider SqlDbType SQL Server Data Provider OracleType Oracle Data Provider

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3.4.3.3   Parameter Mapping

When you add a Parameter object to the Parameters collection of a Command object, the Command object needs to know the relationship between that added parameter and the parameters you used in your SQL query string. Different parameter mappings are used for different Data Providers. Table 3-5 lists these mappings.

Table 3-5. The different parameter mappings Parameter Mapping Associated Data Provider Positional Parameter Mapping ODBC Data Provider Positional Parameter Mapping OLE DB Provider Named Parameter Mapping SQL Server Data Provider Named Parameter Mapping Oracle Data Provider

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3.4.3.3   Parameter Mapping

Both OLE DB and ODBC Data Providers used a so-called Positional Parameter Mapping, which means that the relationship between the parameters defined in an SQL statement and the added parameters into a Parameters collection is one-to-one in the order. In other words, the order in which the parameters appear in an SQL statement and the order in which the parameters are added into the Parameters collection should be exactly identical. The Positional Parameter Mapping is indicated with a question mark ?.

Both SQL Server and Oracle Data Provider used the Named Parameter Mapping, which means that each parameter, either defined in an SQL statement or added into a Parameters collection, is identified by the name. In other words, the name of the parameter appeared in an SQL statement or a stored procedure must be identical with the name of the parameter you added into a Parameters collection.

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3.4.3.4   The Methods of the ParameterCollection Class

To add Parameter objects to an Parameters collection of a Command object, two popular ways are generally adopted, Add() method and AddWithValue() method.

The Add() method is an overloaded method and it has five different protocols, but only two of them are widely used. The protocols of these two methods are shown below.

 ParameterCollection.Add( value As SqlParameter ) As SqlParameter

ParameterCollection.Add( paramName As String, Value As Object )

The AddWithValue() method is similar to the second Add() method with the following protocol:

 ParameterCollection.AddWithValue( paramName As String, Value As Object )

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Questions and Answers……

for creating distributed وانشاء توزيع Integral يتجزأ ال are core to develop a professional data-driven

application يحركها المهنية البيانات لوضع أساسية هي الطلب

Data Provider-dependent components. يعتمد بيانات موفر

المكونات على Functionalities وظائف a table container للجدول حاوية sake of optimal االمثل النحو على حرصا highly recommended يوصى Quite تماما self-explanatory بذاته Credentials اعتماد 04/20/23 اوراق 40

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