ADO.NET Interview Questions and Answers

25. What are the usages of the Command object in ADO.NET?

The following are the usages of the Command object in AD0.NET:

The Command object in AD0.NET executes a command against the database and retrieves a DataReader or DataSet object.

• It also executes the INSERT, UPDATE, or DELETE command against the database.
• All the command objects are derived from the DbCommand class.
• The command object is represented by two classes: SqlCommand andOleDbCommand.
• The Command object provides three methods to execute commands on the database:
  • The ExecuteNonQuery() method executes a Transact-SQL statement against the connection and returns the number of rows affected.
  • The ExecuteScalar() method returns a single value from a database query.
  • The ExecuteReader() method returns a result set by using the DataReaderobject.

26. What are the pre-requisites for connection pooling?

The prerequisites for connection pooling are as follows:

• There must be multiple processes to share the same connection describing the same parameters and security settings.
• The connection string must be identical.

27. What is connection pooling?

Connection pooling refers to the task of grouping database connections in cache to make them reusable because opening new connections every time to a database is a time-consuming process. Therefore, connection pooling enables you to reuse already existing and active database connections, whenever required, and increasing the performance of your application.

You can enable or disable connection pooling in your application by setting the pooling property to either true or false in connection string. By default, it is enabled in an application.

28. What are the various methods provided by the DataSet object to generate XML?

The various methods provided by the DataSet object to generate XML are:

• ReadXml() – Reads XML document into a DataSet object.
• GetXml() – Returns a string containing an XML document.
• WriteXml() – Writes an XML data to disk.

29. Out of Windows authentication and SQL Server authentication, which authentication technique is considered as a trusted authentication method?

The Windows authentication technique is considered as a trusted authentication method because the username and password are checked with the Windows credentials stored in the Active Directory.

The SQL Server Authentication technique is not trusted as all the values are verified by SQL Server only.

30. How would you connect to a database by using .NET?

The connection class is used to connect a .NET application with a database.

31. Which adapter should you use, if you want to get the data from an Access database?

OleDbDataAdapter is used to get the data from an Access database.

32. Which object is used to add a relationship between two DataTable objects?

The DataRelation object is used to add relationship between two DataTable objects.

33. What are different types of authentication techniques that are used in connection strings to connect .NET applications with Microsoft SQL Server?

.NET applications can use two different techniques to authenticate and connect with SQL Server. These techniques are as follows:

• The Windows Authentication option
• The SQL Server Authentication option

34. Explain the new features in ADO.NET Entity Framework 4.0.

ADO.NET Entity Framework 4.0 is introduced in .NET Framework 4.0 and includes the following new features:

• Persistence Ignorance – Facilitates you to define your own Plain Old CLR Objects (POCO) which are independent of any specific persistence technology.
• Deferred or Lazy Loading – Specifies that related entities can be loaded automatically whenever required. You can enable lazy loading in your application by setting the DeferredLoadingEnabled property to true.
• Self-Tracking Entities – Refers to the entities that are able to track their own changes. These changes can be passed across process boundaries and saved to the database.
• Model-First Development – Allows you to create your own EDM and then generate relational model (database) from that EDM with matching tables and relations.
• Built-in Functions – Enables you to use built-in SQL Server functions directly in your queries.
• Model-Defined Functions – Enables you to use the functions that are defined in conceptual schema definition language (CSDL).

35. What is the difference between the Clone() and Copy() methods of the DataSet class?

The Clone() method copies only the structure of a DataSet. The copied structure includes all the relation, constraint, and DataTable schemas used by the DataSet. The Clone()method does not copy the data, which is stored in the DataSet.

The Copy() method copies the structure as well as the data stored in the DataSet.

36. What is the use of DataView?

User-defined view of a table is contained in a DataView. A complete table or a small section of table depending on some criteria can be presented by an object of the DataViewclass. You can use this class to sort and find data within DataTable.

The DataView class has the following methods:

• Find() – Finds a row in a DataView by using sort key value.
• FindRows() – Uses the sort key value to match it with the columns of DataRowViewobjects. It returns an array of all the corresponding objects of DataRowView whose columns match with the sort key value.
• AddNew() – Adds a new row to the DataView object.
• Delete() – Deletes the specified row from the DataView object according to the specified index.