Mumbai University > information technology > sem 4> Web Programming

Marks: 10M

Year : Dec16

ADO.NET Clasess:

ADO.NET provides a bridge between the front end controls and the back end database. The ADO.NET objects encapsulate all the data access operations and the controls interact with these objects to display data, thus hiding the details of movement of data.

The following figure shows the ADO.NET objects at a glance:

1. The DataSet Class:

The dataset represents a subset of the database. It does not have a continuous connection to the database. To update the database a reconnection is required. The DataSet contains DataTable objects and DataRelation objects. The DataRelation objects represent the relationship between two tables.

Following table shows some important properties of the DataSet class:

The following table shows some important methods of the DataSet class:

2. The DataTable Class

The DataTable class represents the tables in the database. It has the following important properties; most of these properties are read only properties except the PrimaryKey property:

The following table shows some important methods of the DataTable class:

3. The DataRow Class

The DataRow object represents a row in a table. It has the following important properties:

The following table shows some important methods of the DataRow class

ADO.NET provides a bridge between the front end controls and the back end database. The ADO.NET objects encapsulate all the data access operations and the controls interact with these objects to display data, thus hiding the details of movement of data.

The following figure shows the ADO.NET objects at a glance:

The DataSet class :

The DataSet is the heart of ADO .NET. The DataSet is essentially a collection of DataTable objects; in turn each object contains a collection of DataColumn and DataRow objects. The DataSet also contains a Relations collection, which can be used to define relations between DataTable objects. There is a Constraints collection, which can be used to define unique keys and data validation rules. There are also DataView objects that work hand-inhand with the DataSet. These objects can be used to define filters, sort orders, and display attributes in a given DataTable. You can change from one DataView to another and instantly change the way data is presented to the user. The DataView is part of the data binding mechanism in ADO .NET.

The DataAdapter Class :

The DataAdapter is used to connect DataSets to databases. It is a go-between class. It is comprised of four Command classes and one DataReader class. The DataAdapter is most useful when using data-bound controls in Windows Forms, but it can also be used to provide an easy way to manage the connection between your application and the underlying database tables, views, and stored procedures. Another way of looking at the DataAdapter class is as a way of containing SQL statements and stored procedures for easy programmatic access. All of the SQL needed to maintain a database entity can be contained in a DataAdapter object. The DataAdapter also uses support classes that will create the SQL statements for updating the database from a predefined Select statement, and will fill the parameter collections of the Command objects contained in the class. There is also a wizard that helps create the DataAdapter and another wizard that will create a DataSet from the Command objects contained within the DataAdapter.

DataReader Class :

The DataReader is used to retrieve data. It is used in conjunction with the Command class to execute an SQL Select statement and then access the returned rows. It provides forward-only read-only access to the data. The DataReader is also used by the DataAdapter to pump data into a DataSet when the Fill method of the DataAdapter is called. The DataReader provides high-speed access to data. You can use a DataReader to pull data for web pages that are read-only, reports, graphs or any other application that does not require data binding and only displays data.

Connection Class :

The connection classes provide the means to connect to the database. They also manage transactions, and connection pooling. In addition, they are used to manage transaction objects. The five main members of this class are ConnectionString, Open, Close, and BeginTransaction. The various parameters for connecting to a database are set via the ConnectionString property. In previous versions of ADO, most of the ConnectionString values were exposed through properties. For security reasons, ADO .NET only exposes the ConnectionString

Command Class :

The Command class provides methods for storing and executing SQL statements and stored procedures. It has a Parameters collection that is used to pass parameters into and out of stored procedures. The collection can also be used to set the parameters for a parameterized SQL statement. The DataAdapter class contains four Command classes for selecting, updating, inserting, and deleting data. The class can also be used by itself for non-databound access to the database. Of all the ADO .NET classes, the Command class is the closest to the ADO Command class in functionality and remains essentially unchanged as far as properties and methods go. Of course, it is a .NET Framework class and does not use COM at all. It also has some enhancements over the old ADO Command object.