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ADO.Net 2.0

Aids in database connectivity

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What Is Database Connectivity

Data used by the applications is stored in a database.

This database is external to the application

It is retrieved into the application as required by the

program. This retrieval is achieved by writing the code that

provides a link between the application & database.

This link is known as database connectivity.

This link is used to send the commands to the database

& getting the corresponding results.

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Role of Microsoft.Net

It has provided classes that aid in the databaseconnectivity.

All these classes are located in the System.Datanamespace.

These classes perform the following tasks

Communication with the database

Storing the data in the database

Fetching the data in the database

Updating the data in the database These classes makes the core data access objects in

.NET Framework

These are collectively known as ADO.NET

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Required NameSpaces

ADO.NET ships with four database clientnamespaces

System.Data.SqlClient

System.Data.Oledb System.Data.Odbc

System.Data.OracleClient

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ADO.NET contains a number of classes thatare used irrespective of the namespace youare using to fetch data

DataSet

DataTable

DataRow

DataColumn

DataRelation

DataColumnMapping

DataTableMapping

Shared Classes

System.Data

System.Data.Common

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Database specific Classes The following classes can be prefixed each with Oledb,

SQL, Oracle, ODBC for respective database Command : wrappers for SQL statements or stored

procedure calls.

CommandBuilder: Used to generate SQL commands Connection: Used to connect to the database

DataAdapter: Used to hold select, insert, update, anddelete commands, which are then used to populate aDataSet and update the Database

DataReader: Used as a forward only, connected datareader

Parameter: Used to define a parameter to a storedprocedure.

Connection: Used for a database transaction, wrapped inan object.

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Database specific Classes The most important feature of the ADO.NET classes is

that they are designed to work in a disconnectedmanner, which is important in today's highly Web-centricworld.

ADO 2.1 introduced the disconnected record set, whichwould permit data to be retrieved from a database,passed to the client for processing, and then reattachedto the server.

This used to be cumbersome to use, becausedisconnected behavior was not part of the originaldesign.

The ADO.NET classes are different in all but one case(the DataReader) they are designed for useoffline from the database.

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Connection A representation of an open connection to the database

It does not perform the following tasks

Doesnt fetch or update data

Doesnt execute queries A Connection object is

A pipeline that commands & queries use to send data& retrieve results

It is a place to set the connection string

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Connection

ConnectionObject

Command&

Queries

Information from

the data source &Returned data

Database

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Connection in Server Explorer Visual Studio provides server explorer as the window to

create connection

This connection can be used in any project

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Connections throug

hData

Wizards

Data Source configuration wizard is used for building thedatabase connection

Using this wizard, you need to select the database path& you end up with a configured connection object readyto use in your application.

Apart from that, the wizard also allows you to select thedatabase objects you want to use in your application

You can also bind your controls with different columns inthe database. Binding is of two types

Simple Binding : 1 Conrtol is bound to 1 column

Complex Binding : 1 Control is bound to many columns

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Different ways of fetching data

DataReader

Stores a single row at a time in the

memory Requires a constant connection with the

database

DataSet

Stores one or more tables Is a disconnected, cached set of records

that are retrieved from the database

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Connection Objects throug

hCode

You can also create connection at runtime by writing thecode to create Connection Object

First of all, you need to select the type of connection youwant.

This choice depends on the database you are connectingcommunicating with

Name Target Data Source

SQL Connection SQL Server Database (2000 onwards)Oledb Connection OLEDB data Source such as Access

ODBC Connection Use DSN

Oracle Connection Oracle databases

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Connection Object Each Connection Object contains the same base

properties, methods & events that are inherited from theSystem.Data.Common.DbConnection class

Properties

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Connection PropertiesName Description

ConnectionString Gets or Set the String to open the connection

ConnectionTimeout Gets the time to wait while establishing the

connection before generating an errorDatabase Gets the name of current database after connection

is open or the database name specified in theconnection string before the connection is opened

DataSource Gets the name of database server to which it isconnected

ServerVersion Gets a string that represents the version of theserver to which the object is connected

State Gets a string that describes the state of theconnection

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SQL Server 2005 Connection The code to connect to SQL Server is:

private SqlConnection sql = new SqlConnection (@"DataSource=user\sqlexpress;InitialCatalog=AdventureWorks;Integrated Security=True");

Or

private SqlConnection sql = new SqlConnection();

sql.ConnectionString = @"DataSource=user\sqlexpress;InitialCatalog=AdventureWorks;Integrated Security=True";

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Commands A command is, in its simplest form, a string of text

containing SQL statements that is to be issued to thedatabase.

A command could also be a stored procedure, or thename of a table that will return all columns and all rowsfrom that table

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Using Commandstring source = @"Data Source=user\sqlexpress;Initial

Catalog=AdventureWorks;Integrated Security=True";

string select = "SELECT ContactName,CompanyNameFROM Customers";

SqlConnection conn = new SqlConnection(source);

conn.Open();

SqlCommand cmd = new SqlCommand(select, conn);

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CommandType Command classes have a property called

CommandType, which is used to define the type of command

CommandType Example

Text (default) String select = "SELECT ContactName FROMCustomers"; SqlCommand cmd = newSqlCommand(select , conn);

StoredProcedure SqlCommand cmd = newSqlCommand("CustOrderHist", conn);cmd.CommandType =

CommandType.StoredProcedure;cmd.Parameters.AddWithValue("@CustomerID", "QUICK");

TableDirect OleDbCommand cmd = newOleDbCommand("Categories", conn);cmd.CommandType =

CommandType.TableDirect;

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Executing Commands ExecuteNonQuery() Executes the command but does

not return any output

ExecuteReader() Executes the command and returnsa typed IDataReader

ExecuteScalar() Executes the command and returns asingle value

In addition to these methods, the SqlCommand classexposes the following method:

ExecuteXmlReader() Executes the command andreturns an XmlReader object, which can be used totraverse the XML fragment returned from the database.

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ExecteNonQuery Used for UPDATE, INSERT, or DELETE statements, where

the only returned value is the number of recordsaffected.

This method can, however, return results if you call astored procedure that has output parameters

string select = "string select = "UPDATE Customers " + "SETContactName = 'Bob' " + "WHERE ContactName = 'Bill'";

SqlCommand cmd = new SqlCommand(select, conn);

int rowsReturned = cmd.ExecuteNonQuery();

Console.WriteLine("{0} rows returned.", rowsReturned);

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ExecuteR

eader This method executes the command and returns a typed

data reader object, depending on the provider in use.

The object returned can be used to iterate through the

record(s) returned

string select = "SELECT ContactName,CompanyNameFROM Customers";

SqlDataReader reader = cmd.ExecuteReader();while(reader.Read())

{

Console.WriteLine("Contact : {0,-20} Company : {1}" ,reader[0] , reader[1]);

}

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ExecuteScalar Used to return a single result from a SQL statement,

such as the count of records in a given table

string select = "SELECT COUNT(*) FROM Customers"; SqlCommand cmd = new SqlCommand(select, conn); object o

= cmd.ExecuteScalar();

Console.WriteLine ( o ) ;

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Calling Stored Procedures Calling a stored procedure with a command object is

a matter of defining the name of the stored procedure,

adding a definition for each parameter of the procedure,

then executing the command with one of the methods

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Stored Procedure The following stored procedure can be created in SQL

Server 2005

This procedure updates the data in the table

CREATE PROCEDURE RegionUpdate (@RegionID

INTEGER, @RegionDescription NCHAR(50))AS

SET NOCOUNT OFF UPDATE Region

SET RegionDescription = @RegionDescriptionWHERERegionID = @RegionID

GO

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Calling the stored procedure from

.Net CodeSqlCommand aCommand = newSqlCommand("RegionUpdate", conn);

aCommand.CommandType =CommandType.StoredProcedure;

aCommand.Parameters.Add(new SqlParameter("@RegionID", SqlDbType.Int, 0, "RegionID"));

aCommand.Parameters.Add(newSqlParameter("@RegionDescription", SqlDbType.NChar,50, "RegionDescription"));

aCommand.UpdatedRowSource =UpdateRowSource.None;

aCommand.Parameters[0].Value = 999;aCommand.Parameters[1].Value = "SouthWesternEngland"; aCommand.ExecuteNonQuery();

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Procedure that returns output

parametersCREATE PROCEDURE RegionInsert(@RegionDescriptionNCHAR(50), @RegionID INTEGEROUTPUT)

AS

SET NOCOUNT OFF

SELECT @RegionID = MAX(RegionID)+ 1 FROM Region

INSERT INTO Region(RegionID, RegionDescription)VALUES(@RegionID, @RegionDescription)

GO

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Calling from .NetSqlCommand aCommand = newSqlCommand("RegionInsert" , conn);aCommand.CommandType =CommandType.StoredProcedure;aCommand.Parameters.Add(new

SqlParameter("@RegionDescription" , SqlDbType.NChar ,50 , "RegionDescription"));aCommand.Parameters.Add(newSqlParameter("@RegionID" , SqlDbType.Int, 0 ,ParameterDirection.Output , false , 0 , 0 , "RegionID" ,DataRowVersion.Default , null));

aCommand.UpdatedRowSource =UpdateRowSource.OutputParameters;aCommand.Parameters["@RegionDescription"].Value ="SouthWest";aCommand.ExecuteNonQuery();int newRegionID = (int)

aCommand.Parameters["@RegionID"].Value;