One of the major component of ADO.NET is the DataSet object, which always remains disconnected from the database and reduces the load on the database.

The DataReader object helps in retrieving the data from a database in a forward-only, read-only mode. The base class for all the DataReader objects is the DbDataReader class.

The DataReader object is returned as a result of calling the ExecuteReader() method of the Command object. The DataReader object enables faster retrieval of data from databases and enhances the performance of .NET applications by providing rapid data access speed. However, it is less preferred as compared to theDataAdapter object because the DataReader object needs an Open connection till it completes reading all the rows of the specified table.

An Open connection to read data from large tables consumes most of the system resources. When multiple client applications simultaneously access a database by using the DataReader object, the performance of data retrieval and other related processes is substantially reduced. In such a case, the database might refuse connections to other .NET applications until other clients free the resources.

The DataSet object provides the following two methods to track down the changes:
• The GetChanges() method - Returns the DataSet object, which is changed since it was loaded or since the AcceptChanges() method was executed.
• The HasChanges() method - Indicates if any changes occurred since the DataSet object was loaded or after a call to the AcceptChanges() method was made.

If you want to revert all changes since the DataSet object was loaded, use the RejectChanges() method.

The IsClosed property is used to check whether a DataReader is closed or opened. This property returns atrue value if a Data Reader is closed, otherwise a false value is returned.

The Fill() method is used to fill the dataset with data.