Download Chapter 3 Introduction to ADO.NET

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
Data Provider
Connection Transaction
DataAdapter
SelectCommand
Command
Your
Application
DataReader
Parameters
DataSet
DataTableCollection
DataTable
InsertCommand
DataRowCollection
UpdateCommand
DataColumnCollection
DeleteCommand
ConstraintCollection
DataRelationCollection
Database
Figure 3-1. A typical architecture of the ADO.NET
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The Architecture of the ADO.NET - 2
Data Provider
Connection Transaction
DataAdapter
Your
Application
DataReader
DataTable
Command
Parameters
DataRowCollection
ExecuteNonQuery
DataColumnCollection
ExecuteScalar
ConstraintCollection
ExecuteReader
DataSet
DataRelationCollection
Database
Figure 3-2. Another architecture of the ADO.NET
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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
System.Data.OleDb
System.Data.SqlClient
System.Data.Odbc
System.Data.OracleClient
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Holds the DataSet and DataTable classes
Holds the class collection used to access an OLEDB data source
Holds the classes used to access an SQL Server 7.0 data source
or later
Holds the class collection used to access an ODBC data source
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:


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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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3.4.1.4 The Oracle Data Provider
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.
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3.4.2 The Connection Class
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.
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3.4.2 The Connection Class
Table 3-3 lists these popular Connection classes used for the
different data sources:
Table 3-3. The Connection classes and databases
Connection Class
Associated Database
OdbcConnection
OleDbConnection
SqlConnection
OracleConnection
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ODBC Data Source
OLE DB Database
SQL Server Database
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:


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
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:



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Microsoft.Jet.OLEDB.4.0 for Access
SQLOLEDB for SQL Server
MSDAORA for Oracle
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The Data Source parameter

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.
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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

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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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3.4.2 The Connection Class
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.
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3.4.2 The Connection Class
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.
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3.4.2 The Connection Class
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;")
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3.4.2 The Connection Class
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 Database
Connection = New OracleConnection("Data Source=XE;" + _
"User ID=system;" + _
"Password=reback")
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3.4.2.1 The Open() Method of the Connection Class
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
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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Figure 3-3. An example coding of the opening a connection
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3.4.2.2 The Close() Method of the Connection Class
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.
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3.4.2.3 The Dispose() Method of the Connection Class
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.
' clean up the objects used
accConnection.Close()
accConnection.Dispose()
accConnection = Nothing
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Figure 3-4. An example coding for the cleanup of resources
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3.4.3 The Command and the Parameter Classes
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.
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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:

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

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).
Dim
Dim
Dim
Dim
sqlCommand
sqlCommand
sqlCommand
sqlCommand
As
As
As
As
New
New
New
New
SqlCommand()
SqlCommand(connString)
SqlCommand(connString, SqlConnection)
SqlCommand(connString, SqlConnection, SqlTransaction)
Figure 3-8. Three popular protocols of the constructor of the Co
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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
ExecuteScalar
ExecuteNonQuery
ExecuteXmlReader (SqlCommand only)
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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.
Retrieves a single value from the database.
Executes a non-query command such as
SQL INSERT, DELETE, UPDATE, and
SET statements.
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).
DimsqlParameter As
DimsqlParameter As
Dim sqlParameter As
Dim sqlParameter As
New
New
New
New
SqlParameter()
SqlParameter(ParamName, objValue)
SqlParameter(ParamName, sqlDbType)
SqlParameter(ParamName, sqlDbType, intSize)
Table 3-4. The data types and the associated Data Provider
Data Type
Associated Data Provider
OdbcType
OleDbType
SqlDbType
OracleType
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ODBC Data Provider
OLE DB Provider
SQL Server Data Provider
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
Positional Parameter Mapping
Named Parameter Mapping
Named Parameter Mapping
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ODBC Data Provider
OLE DB Provider
SQL Server Data Provider
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……
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for creating distributed ‫توزيع وانشاء‬
 Integral ‫ال يتجزأ‬
 are core to develop a professional data-driven
application ‫هي أساسية لوضع البيانات المهنية يحركها الطلب‬
 Data Provider-dependent components. ‫موفر بيانات‬
‫يعتمد‬
‫على المكونات‬
 Functionalities ‫وظائف‬
 a table container ‫حاوية للجدول‬
 sake of optimal‫حرصا على النحو االمثل‬
 highly recommended ‫يوصى‬
 Quite‫تماما‬
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self-explanatory ‫بذاته‬

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