Ado.Net Interview Questions & Answers

1. What is ADO.NET?

• Answer: ADO.NET (ActiveX Data Objects for .NET) is a set of classes in the .NET Framework that provides a data access layer for communication between applications and databases.

2. Differentiate between SqlCommand and SqlDataAdapter.

• Answer: SqlCommand is used to execute SQL commands and stored procedures, while SqlDataAdapter is used to retrieve and update data in a DataSet.

3. Explain the role of the Connection, Command, and DataReader objects in ADO.NET.

• Answer: The Connection object establishes a connection to the database, the Command object executes SQL commands, and the DataReader reads data from the database.

4. How can you open a database connection in ADO.NET?

• Answer: A database connection can be opened using the Open method of the SqlConnection object.

5. What is the purpose of the ExecuteNonQuery method in ADO.NET?

• Answer: The ExecuteNonQuery method is used to execute SQL commands that don't return any data, such as INSERT, UPDATE, DELETE, or DDL statements.

6. Explain the difference between ExecuteScalar and ExecuteReader.

• Answer: ExecuteScalar returns a single value from the first row of the result set, while ExecuteReader returns a DataReader for retrieving multiple rows of data.

7. How can you handle transactions in ADO.NET?

• Answer: Transactions in ADO.NET are handled using the SqlTransaction class. Begin a transaction with BeginTransaction, commit with Commit, and roll back with Rollback.

8. What is a DataSet in ADO.NET?

• Answer: A DataSet is an in-memory representation of data retrieved from a database. It can contain tables, relationships, and constraints.

9. Explain the purpose of DataAdapter in ADO.NET.

• Answer: A DataAdapter acts as a bridge between a DataSet and a database. It populates a DataSet with data from the database and updates changes in the DataSet back to the database.

10. How do you retrieve data from a database using ADO.NET? - Answer: Data retrieval is done using a SqlDataAdapter to fill a DataSet or a SqlDataReader to read data row by row.

11. What is Connection Pooling in ADO.NET? - Answer: Connection Pooling is a mechanism in ADO.NET that reuses existing database connections instead of creating a new connection for each request, improving performance.

12. Explain the purpose of the DataReader.Read method. - Answer: The DataReader.Read method is used to advance the DataReader to the next record in the result set. It returns True if there are more rows to read, and False otherwise.

13. How can you retrieve a single value from a database using ADO.NET? - Answer: Use the ExecuteScalar method of the SqlCommand to retrieve a single value, such as an aggregate result or the value of a single column.

14. What is the role of the CommandBuilder in ADO.NET? - Answer: The CommandBuilder automatically generates SQL commands (INSERT, UPDATE, DELETE) based on the changes made to a DataSet, facilitating the updating of the database.

15. How do you handle exceptions in ADO.NET? - Answer: Exceptions in ADO.NET are handled using Try...Catch blocks. Common exceptions include SqlException and InvalidOperationException.

16. Explain the concept of Data Binding in ADO.NET. - Answer: Data Binding in ADO.NET allows controls on a form to be bound directly to a data source, such as a DataSet, simplifying the display and manipulation of data.

17. What is the purpose of the SqlDataAdapter.SelectCommand property? - Answer: The SqlDataAdapter.SelectCommand property specifies the SQL command to be executed when filling the DataSet or updating the database.

18. How can you prevent SQL injection in ADO.NET? - Answer: To prevent SQL injection, use parameterized queries or stored procedures. Avoid concatenating user inputs directly into SQL commands.

19. Explain the role of the SqlCommandBuilder class. - Answer: The SqlCommandBuilder generates SQL commands for updating the database based on changes made to a DataSet, saving developers from writing manual update statements.

20. What is the purpose of the DataAdapter.FillSchema method? - Answer: The FillSchema method of the DataAdapter is used to populate a DataSet with just the schema (structure) of the result set without the actual data.

21. How can you execute a stored procedure using ADO.NET? - Answer: Use a SqlCommand with the CommandType property set to StoredProcedure, and provide the stored procedure name as the CommandText.

22. What is the purpose of the SqlParameter class in ADO.NET? - Answer: The SqlParameter class is used to define parameters for SQL commands, providing a way to pass values to the SQL command.

23. How do you update changes made in a DataSet back to the database? - Answer: Call the Update method of the DataAdapter, which automatically generates the necessary SQL commands based on the changes made in the DataSet.

24. Explain the concept of optimistic concurrency in ADO.NET. - Answer: Optimistic concurrency involves allowing multiple users to access and modify data concurrently. Changes are checked at the time of updating, and if conflicts are detected, an exception is thrown.

25. How do you check if a record exists in a DataSet before updating it to the database? - Answer: Use the RowState property of the DataRow to check if a record is modified, added, or deleted before attempting to update it.

**26. What is the purpose of the SqlDataSource control

in ADO.NET?** - Answer: The SqlDataSource control is a data source control in ASP.NET that simplifies data access by providing a connection to a SQL database and executing SQL commands.

27. How can you handle multiple result sets in ADO.NET? - Answer: Use the NextResult method of the DataReader to move to the next result set when working with stored procedures or queries that return multiple result sets.

28. What is the purpose of the DataView class in ADO.NET? - Answer: The DataView class is used to apply sorting, filtering, and searching to a DataTable, providing a customized view of the data.

29. How do you handle timeouts in ADO.NET? - Answer: Set the CommandTimeout property of the SqlCommand to specify the maximum amount of time (in seconds) the command is allowed to execute before being terminated.

30. Explain the purpose of the DataAdapter.UpdateBatchSize property. - Answer: The UpdateBatchSize property of the DataAdapter specifies the number of rows that should be processed in a single batch when updating the database, improving performance.

31. What is the purpose of the SqlBulkCopy class in ADO.NET? - Answer: The SqlBulkCopy class is used to perform fast bulk inserts into a SQL Server table from another data source, such as a DataTable or another database.

32. How can you retrieve output parameters from a stored procedure using ADO.NET? - Answer: Set the Direction property of a SqlParameter to ParameterDirection.Output before adding it to the Parameters collection of the SqlCommand.

33. Explain the concept of disconnected architecture in ADO.NET. - Answer: In a disconnected architecture, data is retrieved from the database and stored in a DataSet or DataTable. The connection to the database is closed, allowing manipulation of the data without a continuous connection.

34. What is the purpose of the Fill method in ADO.NET? - Answer: The Fill method of the DataAdapter is used to populate a DataSet or DataTable with data from a data source, such as a database.

35. How do you handle null values in ADO.NET? - Answer: Use the Convert.IsDBNull method to check if a value is DBNull.Value, and handle null values accordingly.

36. What is the purpose of the ConnectionString property in ADO.NET? - Answer: The ConnectionString property of the SqlConnection specifies the details needed to establish a connection to a database, including server name, database name, authentication, etc.

37. Explain the use of the SqlDependency class in ADO.NET. - Answer: The SqlDependency class enables asynchronous notifications when the result set of a query changes, allowing applications to react to changes in real-time.

38. How can you handle Data Concurrency in ADO.NET? - Answer: Data Concurrency in ADO.NET can be handled using optimistic concurrency by checking for changes before updating and handling conflicts that may arise.

39. What is the purpose of the CommandTimeout property in ADO.NET? - Answer: The CommandTimeout property of the SqlCommand specifies the maximum time (in seconds) that a command is allowed to execute before being terminated.

40. Explain the purpose of the DataView.RowFilter property. - Answer: The RowFilter property of the DataView class is used to filter the rows in a DataTable based on a specified expression.

41. How can you improve ADO.NET performance when dealing with large datasets? - Answer: Performance can be improved by using stored procedures, optimizing queries, using appropriate indexes, and employing paging techniques to retrieve data in smaller chunks.

42. What is the purpose of the SqlDataAdapter.SelectCommand.Parameters collection? - Answer: The SqlDataAdapter.SelectCommand.Parameters collection is used to define input parameters for a SQL command or stored procedure before executing it.

43. Explain the purpose of the SqlCommand.CommandType property. - Answer: The CommandType property of the SqlCommand specifies whether the command is a text command, a stored procedure, or a table-direct command.

44. How can you handle data paging in ADO.NET? - Answer: Data paging can be implemented by using the OFFSET and FETCH clauses in SQL Server for SQL Server 2012 and later versions or by using ROWNUM for Oracle.

45. What is the purpose of the SqlDataAdapter.UpdateCommand property? - Answer: The UpdateCommand property of the SqlDataAdapter specifies the SQL command to be used when updating records in the database.

46. How can you implement a transaction with multiple commands in ADO.NET? - Answer: Use the SqlTransaction class to group multiple commands into a single transaction, ensuring that either all commands are executed, or none are.

47. Explain the purpose of the SqlParameter.Direction property. - Answer: The Direction property of the SqlParameter specifies whether the parameter is an input parameter, output parameter, or both.