ADO.NET Interview Questions and Answers for 5 years experience

1. What is ADO.NET?

   • Answer: ADO.NET is a set of .NET Framework classes that provide access to data sources like relational databases, XML files, and other data sources. It's a disconnected architecture, meaning that data is retrieved and processed independently of the data source.

2. Explain the difference between Connected and Disconnected architecture in ADO.NET.

   • Answer: Connected architecture (like ADO) maintains a continuous connection to the database throughout the data access process. Disconnected architecture (ADO.NET) retrieves data into a dataset or datatable, and then closes the connection. This allows for offline processing and improved scalability.

3. What are the main components of ADO.NET?

   • Answer: The main components are: `Connection`, `Command`, `DataReader`, `DataAdapter`, `Dataset`, `DataTable`, and `DataRelation`.

4. What is a Connection object and its purpose?

   • Answer: The `Connection` object represents a connection to a data source. It establishes the link between your application and the database, specifying the server, database name, user ID, and password.

5. Explain the use of the Command object.

   • Answer: The `Command` object encapsulates a SQL statement or stored procedure to be executed against the database. It allows you to specify parameters and retrieve results.

6. What is a DataReader and when would you use it?

   • Answer: A `DataReader` provides a forward-only, read-only stream of data. It's efficient for retrieving large amounts of data when you don't need to modify or navigate backward through the data.

7. Describe the role of the DataAdapter object.

   • Answer: The `DataAdapter` acts as a bridge between the `Dataset` or `DataTable` and the database. It fills the `Dataset` with data from the database and updates the database based on changes made in the `Dataset`.

8. What is a Dataset?

   • Answer: A `Dataset` is an in-memory representation of data. It can contain multiple `DataTable` objects, representing different tables, and `DataRelation` objects, representing relationships between tables.

9. Explain the difference between a DataTable and a DataView.

   • Answer: A `DataTable` is a single table within a `Dataset`. A `DataView` is a dynamic, customized view of a `DataTable` that allows filtering, sorting, and other manipulations without modifying the underlying data.

10. What are DataRelations in ADO.NET?

    • Answer: `DataRelations` define relationships between tables in a `Dataset`, mimicking the relationships in a relational database. They allow you to navigate between related tables.

11. How do you handle transactions in ADO.NET?

    • Answer: Transactions ensure data integrity by grouping multiple database operations into a single unit of work. You use a `Transaction` object to manage the transaction, committing it if all operations succeed or rolling it back if any fail.

12. What are parameterized queries and why are they important?

    • Answer: Parameterized queries use parameters instead of directly embedding values into SQL strings. This prevents SQL injection vulnerabilities and improves performance.

13. Explain the concept of connection pooling.

    • Answer: Connection pooling reuses database connections, reducing the overhead of establishing new connections for each request. This improves performance and scalability.

14. How do you handle exceptions in ADO.NET?

    • Answer: Use `try-catch` blocks to handle potential exceptions like `SqlException` during database operations. Proper error handling ensures application robustness.

15. What are stored procedures and their advantages?

    • Answer: Stored procedures are pre-compiled SQL code stored on the database server. They improve performance, security, and code reusability.

16. How do you execute a stored procedure using ADO.NET?

    • Answer: Set the `CommandType` property of the `Command` object to `CommandType.StoredProcedure` and specify the stored procedure name. Add parameters as needed.

17. What are different ways to update a database using ADO.NET?

    • Answer: You can update a database using `DataAdapter.Update()`, executing individual UPDATE statements via `SqlCommand`, or using stored procedures.

18. Describe different isolation levels in transactions.

    • Answer: Isolation levels control how transactions interact with each other. Options include Read Uncommitted, Read Committed, Repeatable Read, and Serializable.

19. What is optimistic concurrency and how is it implemented in ADO.NET?

    • Answer: Optimistic concurrency assumes that conflicts are rare. It checks for changes before updating, typically using a timestamp or rowversion column.

20. What is pessimistic concurrency and how is it implemented in ADO.NET?

    • Answer: Pessimistic concurrency assumes conflicts are frequent. It locks rows before accessing them, preventing other transactions from modifying them.

21. How do you handle null values in ADO.NET?

    • Answer: Use `DBNull.Value` to represent null values in ADO.NET. Check for `DBNull.Value` before accessing data to avoid exceptions.

22. Explain how to use output parameters in stored procedures with ADO.NET.

    • Answer: Create `SqlParameter` objects with `Direction` set to `ParameterDirection.Output`. After executing the stored procedure, retrieve the output values from the parameter.

23. What are some common ADO.NET performance tuning techniques?

    • Answer: Use parameterized queries, efficient data access methods (like `DataReader`), connection pooling, indexing, and optimize SQL queries.

24. How do you handle large result sets efficiently in ADO.NET?

    • Answer: Use `DataReader` for forward-only access, process data in batches, or consider using techniques like paging.

25. What are the security considerations when using ADO.NET?

    • Answer: Prevent SQL injection by using parameterized queries, secure database credentials, and follow best practices for authentication and authorization.

26. What is the difference between `AcceptChanges()` and `RejectChanges()` methods of a DataTable?

    • Answer: `AcceptChanges()` permanently saves changes made to a `DataTable`. `RejectChanges()` discards all changes and restores the `DataTable` to its original state.

27. Explain the concept of caching in ADO.NET.

    • Answer: Caching improves performance by storing frequently accessed data in memory. ADO.NET doesn't have built-in caching, but you can implement it using techniques like Output Caching or custom caching mechanisms.

28. How do you implement pagination using ADO.NET?

    • Answer: Use SQL `OFFSET` and `FETCH` clauses (or similar techniques depending on the database) to retrieve specific subsets of data for each page.

29. What is the role of the `FillSchema()` method of a DataAdapter?

    • Answer: `FillSchema()` fills a `DataSet` or `DataTable` with schema information (table and column definitions) from the database without retrieving data.

30. How do you handle different database types using ADO.NET?

    • Answer: Use the appropriate provider for each database (e.g., `SqlClient` for SQL Server, `OleDb` for other databases). The connection string specifies the provider.

31. What are some best practices for writing efficient ADO.NET code?

    • Answer: Use parameterized queries, handle exceptions gracefully, close connections promptly, optimize SQL queries, use appropriate data access methods, and consider caching.

32. Explain the use of DataRelation.ChildKeyConstraint.

    • Answer: `ChildKeyConstraint` enforces referential integrity in a `DataRelation`. It prevents adding child rows that violate foreign key constraints.

33. How can you improve the performance of data access operations?

    • Answer: Use efficient queries, indexes, connection pooling, caching, and appropriate data access techniques (DataReader over DataSet for read-only operations).

34. What are the advantages of using stored procedures over inline SQL queries?

    • Answer: Improved performance (pre-compiled), better security (reduced SQL injection risk), reusability, and easier maintenance.

35. Describe how to use transactions to ensure data consistency.

    • Answer: Enclose multiple database operations within a transaction block. If all operations succeed, commit the transaction; otherwise, roll it back.

36. What are the different types of data providers in ADO.NET?

    • Answer: `SqlClient` for SQL Server, `OleDb` for various databases (using ODBC), `OracleClient` for Oracle, and others for specific databases.

37. How do you handle concurrency issues in ADO.NET?

    • Answer: Use optimistic or pessimistic concurrency control mechanisms, depending on your application's needs and the expected frequency of conflicts.

38. Explain the concept of a disconnected architecture and its benefits.

    • Answer: Data is retrieved from the database, the connection is closed, and the data is processed locally. Benefits include scalability and offline capabilities.

39. How do you implement a simple CRUD (Create, Read, Update, Delete) operation using ADO.NET?

    • Answer: Use SQL INSERT, SELECT, UPDATE, and DELETE statements with appropriate parameters through `SqlCommand` objects.

40. What is the purpose of the `BeginTransaction()` method?

    • Answer: Initiates a database transaction, allowing multiple database operations to be treated as a single unit of work.

41. What is the difference between `Close()` and `Dispose()` methods of a Connection object?

    • Answer: `Close()` releases the connection back to the pool. `Dispose()` releases the connection and all related resources.

42. Explain how to handle errors and exceptions during database operations.

    • Answer: Use `try-catch` blocks to handle exceptions (like `SqlException`), provide user-friendly error messages, and log exceptions for debugging.

43. How to retrieve the number of rows affected by an SQL statement?

    • Answer: Access the `RowsAffected` property of the `SqlCommand` object after executing the statement.

44. Explain the importance of using parameterized queries to prevent SQL injection.

    • Answer: Parameterized queries treat user input as data, not as executable code, preventing attackers from injecting malicious SQL code.

45. How can you retrieve data from multiple tables using joins in ADO.NET?

    • Answer: Use JOIN clauses in your SQL statements to combine data from multiple tables based on relationships between them.

46. Describe how to work with different data types in ADO.NET.

    • Answer: Use appropriate .NET data types that correspond to the database column types. Handle type conversions carefully.

47. What are some common performance bottlenecks in ADO.NET applications?

    • Answer: Inefficient SQL queries, lack of indexing, excessive round trips to the database, improper exception handling, and neglecting connection pooling.

48. How can you monitor the performance of your ADO.NET applications?

    • Answer: Use profiling tools, database monitoring tools, and logging to identify performance bottlenecks.

49. Explain the use of the `CommandText` property of the `SqlCommand` object.

    • Answer: `CommandText` specifies the SQL statement or stored procedure name to be executed.

50. What is the role of the `CommandType` property of the `SqlCommand` object?

    • Answer: `CommandType` specifies whether the `CommandText` represents a SQL statement, stored procedure, or table.

51. How do you handle large objects (BLOBs) using ADO.NET?

    • Answer: Use appropriate data types (e.g., `varbinary(max)` in SQL Server) and stream data to and from the database to avoid memory issues.

52. What are some techniques for improving the scalability of ADO.NET applications?

    • Answer: Use connection pooling, optimize queries, employ asynchronous operations, and consider distributed caching.

53. How do you implement data validation in ADO.NET applications?

    • Answer: Use database constraints, client-side validation, and potentially stored procedures to validate data before it's stored in the database.

54. Explain how to use transactions to maintain data integrity across multiple tables.

    • Answer: Enclose all operations affecting multiple tables within a single transaction. If any operation fails, roll back the entire transaction.

55. What are the different ways to handle relationships between tables in ADO.NET?

    • Answer: Use `DataRelation` objects to represent relationships in a `DataSet`, or implement joins in SQL queries.

56. How do you implement logging and tracing in ADO.NET applications?

    • Answer: Use logging frameworks (e.g., NLog, log4net) to record database operations, errors, and performance metrics.

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