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QuestPond: Interview Questions and Answers on ADO.NET

What is the use of command objects?

Command object helps to execute SQL statements. Following are the methods provided by command object: -
  • ExecuteNonQuery: - Executes insert, update and delete SQL commands. Returns an Integer indicating the number of rows affected by the query.
  • ExecuteReader: - Executes select SQL statements which can either be in your .NET code or in a stored procedure. Returns a "Datareader" object.
  • ExecuteScalar: - Executes SQL command and returns only a single value like count, sum, first record etc.

What are Dataset objects?

Dataset is an in memory object with data tables, rows and columns.  You can visualize it as in-memory RDBMS. Dataset has the following features:-
  • The in memory RDBMS works in a disconnected manner. In other words even if the connection is closed the dataset is still there in memory.
  • You can do modification in the in-memory database object and send the final changes to the database.
Below is a simple code snippet which shows how to access a column value.  You can see how the full dataset object hierarchy is accessed to get the column value.


See following video on Dataset is a disconnect while datareader is connected: -

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Shivprasad koirala Koirala
I am a Microsoft MVP for ASP/ASP.NET and currently a CEO of a small E-learning company in India. We are very much active in making training videos , writing books and corporate trainings. Do visit my site for .NET, C# , design pattern , WCF , Silverlight , LINQ , ASP.NET , ADO.NET , Sharepoint , UML , SQL Server training and Interview questions and answers
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