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ADO.NET

One problem with ADO is that it was originally created as a connected database

access object model. This means that developers primarily use a Recordset object while connected to the data source. Microsoft modified the recordset to allow disconnected

access, but this solution did not work as well as if it had been designed as a disconnected

data access model from the beginning. The recordset object can contain only one result set. This means we cannot relate result sets using a primary key / foreign key type of

relationship and we cannot relate result sets from different data sources.

With .NET, Microsoft developed an entirely new data model that uses the provider wrapper technology but eliminates the old-style recordset object. That new data model is

ADO.NET.

ADO.NET still uses Connection and Command types, but it replaces the Recordset with two data types- DataReader and DataSet objects.

The DataReader object provides connected data access. The DataSet, the core object

of ADO.NET is an in-memory cache of disconnected data.

ADO.NET is a set of classes that allow .NET based applications to read and update

information in databases and other data sources. You can access these classes through the

System.Data namespace provided by the .NET framework.

ADO.NET provides consistent access to a wide variety of data sources including

Microsoft SQL Server database, OLEDB compliant databases, non-relational sources such as

Microsoft Exchange Server and XML documents.

Benefits of ADO.NET:

ADO.NET provides many benefits to experienced developers including-

1. Similar Programming model to that of ADO

2. Designed for Disconnected Data-

ADO.NET is designed for working with disconnected data in a multitier environment.

It uses XML as the format for transmitting disconnected data, which makes it easier to

communicate with client applications that are not based on windows.

3. Intrinsic to the .NET Framework-

Because ADO.NET is intrinsic to the .NET Framework, you have all the advantages of using the .NET framework, including ease of cross-language development.

4. Supports XML-

ADO and XML have previously been incompatible. ADO was based on relational data, and XML is based on hierarchical data. ADO.NET brings together these two data access

techniques and allows you to integrate hierarchical and relational data, as well as alternate

between XML and relational programming models.

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ADO.NET Architecture:

ADO.NET Class Structure:

We can divide the ADO.NET related classes into three groups.

.NET Provider Classes:

These classes interface with the database and provide some features for manipulating the retrieved data. Each data provider will have a different set of

classes. For example, the SQL provider has sqlConnection, sqlCommand etc., we can

easily pass data between these classes and the consumer classes.

Data Consumer Classes:

We use these classes for manipulating data. They are independent of the data source

and we can manipulate data using these classes without an open connection to the databases.

Other .NET Framework Classes:

These classes are related to data handling but are not part of the System.Data

namespace. For example, Data-Bound controls. These are part of the System.Windows.Forms namespace. We can easily pass data between these classes

and Data Consumer Classes.

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.NET Data Providers:

In ADO.NET each particular type of data source has a .NET data provider. ADO.NET

is providing managed providers for accessing data sources. They are:

SQL Server .NET Provider:

System.Data.SqlClient.dll Assembly

sqlConnection, sqlCommand, sqlDataReader, sqlTransaction, sqlParameter are the classes under this namespace.

OLEDB .NET Provider:

This provider is used to access oracle, MS-Access and other data sources that support the Microsoft OLEDB data component interface.

System.Data.OleDb.dll Assembly

OleDbConnection, OleDbCommand, OleDbDataReader etc., are the classes.

ODBC .NET provider:

System.Data.Odbc.dll Assembly

OdbcConnection, OdbcCommand, OdbcDataReader etc., are the classes.

ORACLE .NET Provider:

System.Data.OraClient.dll Assembly

OraConnection, OraCommand, OraDataReader etc., classes.

.NET Provider Classes:

The provider classes for the SQL Server .NET Provider are derived from System.Data.SqlClient namespace. All begin with sql keyword. The classes for the OLEDB

provider begin with OleDb etc., The classes for the OraClient provider begin with Ora and

the classes with ODBC provider begins with Odbc. The classes are:

xxxConnection Class:

The connection objects are the first objects that use and they are required before

using any of the other ADO.NET provider objects. They provide the basic connection to your data source. If you are using a database that required a UserID and Password, or one on a

remote network server, the connection object takes care of the details of establishing the

connection and logging in.

Common Properties and methods of the Connection Class:

MemberName Propter(p)/

Method(m)

Description

ConnectionString P Establishes the connection to the data source.

Provider specific.

ConnectionTimeOut P Specifies the length of time(in sec) to attempt to

connect

State P Get the state of the connection Connected,

Connecting, notConnected.

Provider P Used by oledb connection object to specify which

oledb provider will be sued to communicate

Data Source/server P Server name

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Initial catalog P Name of the database

Userid P

Password P

Interated Securith P Whether a connection is a secure connection

Open M Attempts to open the connection object based on

the connection string.

Close M Closes the connection to the data source

BeginTransaction M Begins a database transaction.

Ex: sqlConnection Con=new SqlConnection();

//using SQL Data Provider with Windows Authentication

Con.ConnectionString=Integrated Security=true;data source=(local);initial

catalog=university

//using SQL Data Provider with SQL Server Authentication

Con.ConnectionString=Integrated Security=true;data source=(local);initial

catalog=university;uid=sqlclass;pwd=sql

//using OleDb Data Provider

Con.ConnectionString=provider=sqloledb;data source=(local);intitial

catalog=university;uid=;pwd=;

Con.Open();

//using Oracle

OleDbConnection oleCon=new OleDbConnection();

OleCon.ConnectionString=provider=msdaora.1;userid=; pwd=;

OleCon.open()

XXXCommand Class:

You can use the ADO.NET command object to execute commands and optionally, to return

data from a data source.

Steps in using Command object:

1. create a command object.

2. Use the CommandType property to specify the type of command to be executed.

CommandType.StoredProcedure

CommandType.Text

CommandType.Table

3. Use CommandText property and specify the command to be executed in case of Text

type and name of the object in case of stored procedure or table name.

4. Use one of the Execute menthod to execute the command.

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Executing Commands:

You can execute a command within a valid and open connection. The command object

provides 3 methods that you can use to execute commands.

ExecuteReader():

Use this method when the query will return a stream of data such as a Select Statement

returning a set of records. This method returns the records in a DataReader object.

ExecuteScalar():

Use this method when the query will return a singleton value. For example, a select statement

returning an aggregate value. It executes the query and returns the first column of the first row in the

result set, ignoring any other data that is returned.

ExecuteNonQuery():

Use this method when the query will not return a result;ex: insert statement.

Ex:

sqlCommand cmd=new sqlCommand();

cmd.CommandType=CommandType.Text;

cmd.CommandText=select * from emp;

sqlDataReader dr;

dr=cmd.ExecuteReader();

DataReader Class:

DataReader object is used to create a read-only, forward-only stream of data. This is an

efficient method for accessing data that you only need to read through code. You can improve the app

performance by using this object. Because, it holds only a single row at a time in memory instead of

caching the entire set of records.

Reading Data:

You can instantiate the DataReader object by using the ExecuteReader method of command

object. After you create the DataReader, you can call the Read method to obtain data in the rows.

You can access the columns by name, ordinal number or native type in conjunction with ordinal

number.

Ex: While dr.Read()

{

------

}

You must ensure that you sued the Close method of the DataReader object before accessing

any output or return parameter from a StoredProcedure.

Retrieving Data:

Assume that dr is the DataReader, then we can use any one of the following ways to retrieve the

data.

dr.Item[0];

dr[0];

dr[Empid];

dr.GetString[0];

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Using Command Object with Stored Procedure:

I. Create a Command object

sqlCommand cmd=new sqlCommand();

II. Set the CommandType property of command object to stored proecure.

cmd.CommandType=CommandType.StoredProcedure;

III. Specify the procedure name in CommandText property.

cmd.CommandText=spGetEmployee;

IV. Use the sqlParameter class to create a parameter object depending on the type and direction

of the parameter in the procedure

sqlParameter param1=new sqlParameter(@eid,sqlDbType.int);

param1.Direction=ParameterDirection.Input;

V. Set the value of the parameter;

Param1.Value=Convert.ToInt32(txtEmpid.Text);

VI. Add the parameter to the parameter Collection.

cmd.Parameters.Add(param1);

VII. Execute the command object;

dr=cmd.ExectueReader();

DataSet

DataSets are the primary objects that you will work with when accessing disconnected sets of

data. They are similar in concept to groups of ADO disconnected recordsets, but in ADO.Net there are

many enhancements including the ability to relate tables together.

DisConnected Data in RDO and ADO:

RDO and ADO introduced the concept of disconnected data. This was implemented so that you

could retrieve a set of records, disconnected from the data source, and work with the data locally. You

could reconnect and submit your changes to the database. The recordsets were marshaled between

the tiers as COM objects, requiring that both the server and client computer could handle COM

Components

Disconnected Data in ADO.NET:

ADO.Net is a designed for use in the internet world, where as COM may not be supported by

all tiers, and may not be transmitted through fire walls. ADO.Net uses XML as its transmission format.

This is a text based format. It avoids the problems associated with the transmission of COM objects

and ensuring true cross-platform interoperability.

ADO.Net provides you with a new object for the caching of data on the client computer. This

object is known as DataSet. This subject is automatically disconnected from the datasource but

maintain the ability to later update the source based on changes made at the client.

DataSet acts like in-memory database for the client application by maintaining collection of

tables belonging to different data sources in the form of XML Storage.

Dataset is always disconnected and the information will be filled into the dataset.

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The DataSet can be used in different ways to retrieve data.

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Creating DataSets:

Syntax:

DataSet ds=new DataSet(); (or)

DataSet ds=new DataSet(Table1);

Populating DataSets:

You can use the DataAdapter objects Fill method to access data stored in the datasource,

and store the data in DataTables within a DataSet in your application.

Syn: DataAdapter1.Fill(DataSetName,TableName)

Ex: da.Fill(ds,Table1);

DataAdapter:

You can use the DataAdapter to exchange data between a data source and a DataSet. You can

use it to retrieve appropriate data and insert it into DataTable objects within a DataSet and to update

changes from the DataSet back to the datasource.

Creating a DataAdapter:

Ex: sqlDataAdapter da=new sqlDataAdapter(Select * from table1,con)

Fill method is used to populate the dataset with datasource information.

Update method is used to save the changes from dataset back to the datasource.

The Fill method will perform the following tasks:

It will establish the connection to the database server

It sends the Select Statement to the database server for execution

It creates a table in the dataset and gets the information from database server using implicitly

DataReader

It will closes the connection.

Updating Data in DataSet:

After you have created a DataSet of DataTables, you might want to add, update and delete

data. Any changes you make to the data are stored in memory and later used to apply changes to the

data source.

Adding Rows:

1. Instantiate a DataRow object by using NewRow method tof the DataTable

2. Populate the columns with data.

3. Call the Add method of the DataRows collection, passing the DataRow object.

Editing Rows:

1. Call the BeginEdit method of the row

2. Change the data in the Columns

3. Call EndEdit or CancelEdit to accept or reject changes

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Deleting Data:

Use either of the following methods to delete a row.

Remove

Call the Remove method of the DataRow collection. This permanently removes the row

from the dataset

Delete

Call the Delete method of the DataRow object. This only makes the row for deletion in

the dataset and calling reject changes will undo the deletion.

Confirming Changes:

To update the DataSet, you use the appropriate method to edit the table and then you call

AcceptChanges or RejectChanges for the individual rows or for the entire table.

You can discover whether any changes have been made to a row since AcceptChanges was

last called by querying its RowState property. It contains the following values.

Enumeration Desc Value

UnChanged No changes have been made 2

Added The row has been added to the

table

4

Modified Something in the row has been

changed

16

Deleted The row has been deleted by

the delete method

8

Detached The row has been deleted with

Remove method or row has

been created, but the add

method has not been called

1

Updating Data at the Source:

After you have updated the tables in your dataset, you will want to replicate those changes to

the underlying data source. To do this, you use the Update method of the DataAdatper object.

The Update method like fill method takes two parameters.

1. The Dataset in which the changes have been made

2. The name of the table in which changes are made.

This method determines the changes to the data and execute appropriate SQL

Command against the source data.

Automatically Generating Changes:

If your datatable is generated from only one table in the datasource, you can use the

commandBuilder object to automatically create the InsertCommand, DeleteCommand,

UpdateCommand properties

Ex:

sqlCommandBuilder cb=new sqlCommandBuilder(da);

da.Update(ds,table1);