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Chapter 21
Connecting to the database
Executing Commands – ADO.NET
Stored Procedures
The ADO.NET object model
Using XML and XML schemas – ADO.NET is built upon an
XMLframework
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ADO .NET a new approach
ADO.NET ships with 2 client namespaces –
One for SQL Server
The other for database exposed through an OLE DB interface
Namespaces


System.Data = all generic data access classes
System.Data.Common – Classes shared (or overridden) by individual
data providers

System.Data.OleDb – OLE Db provider classes

System.Data.Sqlclient – SQL Server provider classes

System.Data.SqlTypes – SQL Server data types
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Shared classes
a number of classes regardless of whether program is using SQL Server or
OLE DB classes
System.Data Namespace:






DataSet - The object may contain a set of DataTables, can include
relationships between these tables, and is designed for disconnected
use
DataTable – A container of data. Da DataTable consists of one or
more DataColumns, and when populated will have one or more
DataRows containing data
DataRow – A number of values – a row from the table or spreadsheet
DataColumn – Contains the definition of a column, name and data
type
DataRelation – A link between two DataTables within a DataSet.
Constraint – Defines a rule for a DataColumn ( or a set of Data
Columns), such as unique values
System.Data.Common Namespace


DataColumnMapping – Maps the name of a column from the
database with the name of a column within a DataTable
DataTableMapping – Maps a table name from the database to a
DataTable within a DataSet
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Database Specific Classes
Implement a set of standard interfaces defined within the Syste.Daata
namespace







SqlCommand, OleDbCommand – Awrapper for SQL statements or
stored procedure calls
SqlCommandBuilder, OleDbCommandBuilder – A class used to
generate SQL commands ( such as INSERT, UPDATE, an DELETE
statements) from a SELECT statement
SqlConnection, OleDbConnection – The connection to the database.
SqlDataAdapter, OleDbDataAdaper – A class used to hold select,
insert, update and delete commands, which are then used to populate a
DataSet and update the Database
SqlDataReader, OleDbDataReader – A forward only, connected
data reader
SqlParameter, OleDbParameter – Defines a parameter to a stored
procedure
SqlTransaction, OleDbTransaction – A database transaction,
wrapped in an object
Most important feature – ADO.NET is designed to work in a disconnected
manner
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Using Database Connections
How to create, open and close a connection
using System.Data.SqlClient
// parameters are delimited by semicolon
string source = “server=(local)\\NetSDK;” +
“uid=QSUser;pwd=QSPassword;” +
“databae=Northwind”;
SqlConnection conn = new SqlConnection(source);
Conn.Open();
// do something
conn.Close();
Using Connections Efficiently
Keeping sessions open too long can affect other applications
Closing should be considered mandatory
Two main ways to ensure database connections (or other resources) are
release:

try – catch and finally block

using block
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Lab 6b
string source = "server=HOME\\NetSDK;" +
"integrated security=SSPI;" +
"database=Northwind";
SqlConnection conn = new SqlConnection(source);
// make sure data base gets closed
try
{
// open connection
conn.Open();
// Do something
MessageBox.Show("Data base is opon");
}
catch (Exception ex)
{
// do something
}
finally
{
MessageBox.Show("Data Base is clsoing");
conn.Close();
}
//
//
//
//
The using Block ensures that the data base connection is closed
in addtion if the using block is used within the try block
and an exception occurs the Idisoposable.Dispose method
will be called on the resource guarded by the using clause
try
{
string source2 = "server=HOME\\NetSDK;" +
"integrated security=SPPI;" +
"database=Northwind";
using (SqlConnection conn2 = new SqlConnection(source2))
{
conn2.Open();
MessageBox.Show("using block");
// do something
// close myselft - optional since Close will be called
}
}
catch (Exception e2)
{
// dos something
MessageBox.Show("in catch Block");
}
finally
{
// ensure close
MessageBox.Show("In finally block");
conn.Close();
}
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Transactions
Updates within the scope of a transaction
string source = "server=HOME\\NetSDK;" +
"integrated security=SSPI;" +
"database=Northwind";
SqlConnection conn = new SqlConnection(source);
conn.Open();
SqlTransaction tx = conn.BeginTransaction();
// execute command
tx.Commit();
conn.Close();
Isolation Levels – determines how changes are made in one database
session are viewed by another – (page 692)
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Commands
string source = "server=HOME\\NetSDK;" +
"integrated security=SSPI;" +
"database=Northwind";
string select = “SELECT ContactName, CompanyName FROM
Customers”;
SqlConnection conn = new SqlConnection(source);
conn.Open();
SqlCommand cmd = new SqlCommand(select ,conn);
Command Type enumerations
Text (default)
StoredProcedure
TableDirect
Set command type: cmd.CommandType = ….
Exucuting commands
 ExecuteNonQuery() – Executes the command but dows not return
any output
 ExecuteReader() – Executes the command and returns a typed
IdataReader
 ExecuteScalar() – Exeucctes the command and returns a single
value
The SqlCommand class aso exposes the method
 ExecuteXmlReader() – Executes the command and returns an
XmlReader object, which can be used to traverse the SML
fragment returned from the database
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Fast Data Access:
The Data Reader
 The data reader is the simplest and fastest way of selecting some
data from a data source
 However, it has the least capabilities
 Cannot directly instantiate a data reader object –an instance is
returned from the appropriate databe’s command object (ex
SqlCommand) after having called the ExcuteReder() method
 Keeps the database open until it is closed
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using System;
using System.Data.OleDb;
public class DataReader
{
public static int Main(string[] args)
{
string source = "Provider=SQLOLEDB;" + Login.Connection ;
string
select = "SELECT ContactName,CompanyName FROM Customers" ;
OleDbConnection conn = new OleDbConnection ( source ) ;
try
{
conn.Open ( ) ;
OleDbCommand cmd = new OleDbCommand ( select ,
conn ) ;
OleDbDataReader aReader = cmd.ExecuteReader ( ) ;
while ( aReader.Read ( ) )
Console.WriteLine ( "'{0}' from {1}" , aReader.GetString(0) ,
aReader.GetString ( 1 ) ) ;
aReader.Close ( ) ;
conn.Close ( ) ;
}
catch ( Exception e )
{
Console.WriteLine ( e ) ;
Console.WriteLine ( ) ;
Console.WriteLine ( "Chances are your database does not have a user" ) ;
Console.WriteLine ( "called QSUser, or you do not have the NetSDK “ +
“ database installed." ) ;
}
return 0;
}
}
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The DataSet