Download Overview of ADO.NET

Overview of ADO.NET
ODBC, OLE-DB, and OLE-DB.NET Providers
Communication with databases has been typically performed through some
proprietary interfaces such as Open Database Connectivity (ODBC) or
Object Linking and Embedding Database (OLE-DB). These interfaces
translate commands between your application and the database. These
software are provided as part of the Microsoft Data Access Components
(MDAC) free from Microsoft.
 ODBC drivers are used to provide access to an ODBC compliant
database, including both Microsoft products (Access, SQL Server)
and non-Microsoft products (Oracle, DB2).
 OLE-DB providers are available for most common data stores,
including Access, SQL Server, and Exchange Server.
A Web application interfaces with the database through a set of objects
defined in the ActiveX Data Objects (ADO) model. The ADO objects
interface with the database via the ODBC and OLE-DB.
The .NET framework changed the ways we used to access and manipulate
the database, although the fundamental steps of accessing and
manipulating the database are not changed. Thus an ASP.NET application
interacts with the ADO.NET objects built into the ADO.NET Model. Then
ADO.NET uses the interface via the .NET manage provider to access the
database.
Thus, if your application accesses the Microsoft Access data using ADO
objects, and you upgrade your data to a SQL Server database, you will
only need to have a few changes within your application. The ADO
interface to the data will remain the same for most of your application.
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Working with the Database
There are few general steps that are required to communicate between a
Web page and a database:
1. Build database tables and queries.
2. Create a connection to the database. The connection identifies the
location of the database (the data source) and the connection method
(an ODBC driver, OLE-DB provider, or an OLE-DB.NET data
provider), along with any other settings such as username or
password.
3. Create an ASP.NET Web page.
4. Add an ADO.NET connection object that connects to the database,
executes commands, and returns data from the database.
5. Create code that will interact with the data, display the data in an
ASP.NET control, perform calculations on the data, or upload
changes to the database.
ADO Object Model
The Microsoft ActiveX Data Object Model (ADO) has been the preferred
method of communication with the database. It provided a set objects that
were used to open a database connection, fetch a recordset from the
database and perform a set of database operation such as , display, insert,
delete, and update database records.
In the ADO model, when a recordset is being opened, it would keep the
connection active with the database until looping through the recordset is
completed. For a Web connection, this would require a lot of resources for
the server when many browsers are communicating with the server at the
same time.
ADO.NET Object Model
The Web itself employs a disconnected client-server approach. That is,
after a page is received from the server, the connection between the
browser and the Web server is broken. The ADO.NET model is built on the
same principle. It separates the process of connecting to the data source
from the manipulation of the data.
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The ADO.NET model consists of several components, the two central
components are: the DataSet and the .NET Data Provider. The .NET data
provider is a set of components including the Connection, Command,
DataReader, and DataAdapter objects.
The ADO.NET DataSet is the core component of the disconnected
architecture of ADO.NET. The DataSet is explicitly designed for data
access independent of any data source. As a result it can be used with
multiple and differing data sources, used with XML data, or to manage data
local to the application. The DataSet contains a collection of one or more
DataTable objects made up of rows and columns of data, as well as
primary key, foreign key, constraint, and relation information about the data
in the DataTable objects. It replaces the RecordSet object of the ADO
architecture.
The other core element of the ADO.NET architecture is the .NET data
provider, whose components are explicitly designed for data manipulation
and fast, forward-only, read-only access to data. The Connection object
provides connectivity to a data source. The Command object enables
access to database commands to return data, modify data, run stored
procedures, and send or retrieve parameter information. The DataReader
provides a high-performance stream of data from the data source. Finally,
the DataAdapter provides the bridge between the DataSet object and the
data source. The DataAdapter uses Command objects to execute SQL
commands at the data source to both load the DataSet with data, and
reconcile changes made to the data in the DataSet back to the data
source.
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Managed Providers (.NET Data provider)
A .NET data provider is used for connecting to a database, executing
commands, and retrieving results. Those results are either processed
directly, or placed in an ADO.NET DataSet in order to be exposed to the
user in an ad-hoc manner, combined with data from multiple sources, or
remoted between tiers.
The following table outlines the four core objects that make up a .NET data
provider.
Object
Connection
Command
DataReader
DataAdapter
Description
Establishes a connection to a specific data source.
Executes a command against a data source. Exposes
Parameters and can execute within the scope of a Transaction
from a Connection.
Reads a forward-only, read-only stream of data from a data
source.
Populates a DataSet and resolves updates with the data source.
The ADO.NET Objects communicate to the data sources through the
managed providers. There are two managed providers in ADO.NET:
 SQL Server.NET data provider is used to connect to a SQL Server
database version 7.0 or later. It provides a direct communication with
the SQL Server database using a protocol called TDS (Tabular Data
System) which provides performance improvement.
 OLE-DB.NET data provider is used to connect to any other data
source including SQL Server, Access database, XML file, or any
other database. It does not provide specific performance
improvement.
Driver
SQLOLEDB
MSDAORA
Microsoft.Jet.OLEDB.4.0
Provider
Microsoft OLE DB Provider for SQL Server
Microsoft OLE DB Provider for Oracle
OLE DB Provider for Microsoft Jet (like Access)
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ADO.NET Objects by Data Provider
There are basically four objects in the ADO.NET: Connection, Command,
DataReader, and DataAdapter. Depending on the data provider, the names
of these objects are different. There is also a Dataset object that is part of
the ADO.NET object model as shown in the figure. The names of the
objects are different depending on the data provider.
 SQL Server .NET data provider
o SqlConnection,
o SqlCommand,
o SqlDataReader, and
o SqlDataAdapter
 OLE-DB data provider (like Access)
o OleDbConnection,
o OleDbCommand,
o OleDbDataReader, and
o OleDbDataAdapter.
 DataSet object - to retrieve data from the database.
ASP.NET Application
DataReader Object
Command Object
Data Adapter Object
DataSet Object
Connection Object
Managed Data
Provider
Data Source
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The Connection Object
The ADO.Net Connection Object provides the connection to the database.
It requires a connection string that can be written through codes or it can
be configured through the Data Connections window of Visual Studio.NET
environment.
The connection string requires the following fields:
 Provider – The name of the managed provider for the SQL Server or
OLE-DB Provider.
 Data Source – The name of the SQL Server computer or full path of
the database like Access.
 Initial Catalog – The name of the database in case of database like
SQL Server.
 User ID and Password – It identifies the authentication for
databases like SQL Server. The default user ID in SQL Server is sa
and password is blank.
Sample OLE-DB connection string to a SQL Server or similar database:
Dim CS as String
CS = "Data Source=MyServer; Initial Catalog=MyDatabase;
User ID=sa; PASSWORD=;"
Sample OLE-DB connection string to Access Database:
Dim CS as String
CS = "Provider=Microsoft.Jet.OLEDB.4.0;
Data Source=c:\Mypath\Northwind.mdb”
When the full path of the Access database is not known, the path can
be obtained by using the mappath method of the server object. For
example:
Dim CS as String
CS = "Provider=Microsoft.Jet.OLEDB.4.0;
Data Source= “ & server. mappath (“Northwind.mdb”)
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The Command Object
The command object is used to execute a command to process an SQL
query, a stored procedure, or a table from a database. Following are the
methods and properties of the command object.
 Connection property - The Connection used by the Command
object
 CommandText property - identifies the command to execute
 CommandType property - indicates the type of command being
executed
o Text - by default, indicates that the command is an SQL text
string
o TableDirect - specifies the name of a table to return
o StoredProcedure - specifies the name of a stored procedure
 ExecuteReader method - executes the command and passes the
results to the DataReader object
 ExecuteNonQuery method - does not return rows because it’s used
to insert, modify, and delete data, but returns an integer of the
number of rows affected by the command
For example, the command object is constructed by providing a SQL query
and a connection object as parameters, and then a method is used to
execute the query.
Dim CS As String, Sql As String
CS = "Provider=Microsoft.Jet.OLEDB.4.0;
Data Source= “ & server. mappath (“Northwind.mdb”)
Dim myConnection As OleDbConnection
myConnection = New OleDbConnection(CS)
Sql = “Select * from Customer”
Dim myCommand As New OleDbCommand(Sql, myConnection)
myConnection.Open()
myCommand.ExecuteNonquery()
myConnection.Close()
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The DataReader Object
The data reader object




delivers a stream of data from the database.
provides a high-performance method of accessing read-only data.
read-only, forward-only stream of data from the database.
requires continual access to the database, while the DataAdaptor
uses a disconnected dataset to access the data.
 It holds one row in memory at a time, as opposed to DataDet which
holds a complete table in memory.
The methods and properties of DataReader object are:
 ExecuteReader method - retrieves rows of data as they are located
in the database.
 Read - returns a single row and caches each row in memory only
once, then moves the current record pointer to the next record or row.
 CommandBehavior property - closes the connection.
 Close method - closes the DataReader object and releases the
references to the rowset.
Foe example, the ExecuteReader method is used on command object to
return a resultset from the database.
Dim CS As String, Sql As String
CS = "Provider=Microsoft.Jet.OLEDB.4.0;
Data Source= “ & server. mappath (“Northwind.mdb”)
Dim myConnection As OleDbConnection
myConnection = New OleDbConnection(CS)
Sql = “Select * from Customer”
Dim myCommand As New OleDbCommand(Sql, myConnection)
myConnection.Open()
Dim dR As OleDbDataReader
dR = myCommand.ExecuteReader()
myConnection.Close()
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The DataAdapter Object
The DataAdapter Object accesses a DataSet object. It is the only way that
a database data can be manipulated (insert, delete, update). Because the
DataSet is disconnected, there must be methods used to maintain the
original set of data, and the changes.
The Methods and Properties of the DataAdapter are:
 Fill method acts as the bridge between the datasource and the
DataSet. It loads the data stored in the DataAdapter to the DataSet
object.
 SelectCommand method is used to retrieve data.
 InsertCommand method is used to add a new record.
 UpdateCommand method is used to modify the data within an
existing record.
 DeleteCommand method is used to permanently remove a record
from the database.
For example,
Dim CS As String
CS = "Provider=Microsoft.Jet.OLEDB.4.0;
Data Source= “ & server. mappath (“Northwind.mdb”)
Dim myConnection As OleDbConnection
myConnection = New OleDbConnection(CS)
Dim Sql As String
Sql = “Select * from Customer”
Dim myAdapter As OleDbAdapter
myAdapter = New OleDbAdapter(Sql, myConnection)
Dim ds As New DataSet
myAdapter.Fill (ds, “Masters”)
Here “Masters” is the table where data is returned.
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The DataSet Object
The RecordSet object in ADO has been dropped; instead a new object
called DataSet is introduced in ADO.NET.
 The DataSet object is a disconnected collection of one or more tables
that are stored in memory.
 The DataSet is effectively a private copy of the database in the
memory, complete with tables, columns, relationships, constraints,
and data. However, it may not necessarily reflect the current state of
the database.
 If you want to see the latest changes made by other users, you can
refresh the dataset by calling the appropriate Fill method of the
DataAdapter object.
 A DataSet not only can receive data from a database, but also from
files such as XML, text, Excel, and so on.
A DataSet contains a DataTable collection, which in turn contains other
collections such as DataRow, DataColumn, and DataConstraint.
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