ADO.NET Interview Questions and Answers for 10 years experience

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100 ADO.NET Interview Questions and Answers

  1. What is ADO.NET?

    • Answer: ADO.NET is a set of .NET Framework classes that provide data access services to applications. It allows developers to connect to various data sources, execute queries, and retrieve, manipulate, and update data.

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

    • Answer: Connected architecture (e.g., using `SqlConnection` directly) maintains a persistent connection to the database throughout the data access process. Disconnected architecture (using `DataSet` and `DataAdapter`) retrieves data into a local cache, allowing operations even without an active database connection. Disconnected offers better scalability and performance for large datasets.

  3. What are the different data providers in ADO.NET?

    • Answer: Common data providers includeSqlClient (for SQL Server), OleDb (for older databases like Access), ODBC (for various databases), and OracleClient (for Oracle). Each provides a set of classes tailored to a specific database system.

  4. Describe the role of Connection, Command, DataReader, and DataAdapter objects in ADO.NET.

    • Answer: `Connection`: Establishes a connection to the database. `Command`: Represents a SQL statement or stored procedure to be executed. `DataReader`: Provides a forward-only, read-only stream of data from a database query. `DataAdapter`: Facilitates data transfer between a `DataSet` and a data source, handling queries, inserts, updates, and deletes.

  5. What are transactions and how are they implemented in ADO.NET?

    • Answer: Transactions ensure data integrity by grouping multiple database operations into a single unit of work. If any operation fails, the entire transaction is rolled back. In ADO.NET, they're implemented using `TransactionScope` (for distributed transactions) or by explicitly starting and committing/rolling back transactions using the `Connection` object's methods.

  6. Explain the concept of parameterized queries and their benefits.

    • Answer: Parameterized queries use placeholders for values instead of directly embedding them in SQL. This prevents SQL injection vulnerabilities, improves performance (by reusing query plans), and enhances code readability and maintainability.

  7. How do you handle exceptions during database operations in ADO.NET?

    • Answer: Use `try-catch` blocks to handle potential exceptions like `SqlException` (for SQL Server). Ensure proper resource cleanup (closing connections, readers, etc.) using `finally` blocks or `using` statements.

  8. What are stored procedures and why are they used?

    • Answer: Stored procedures are pre-compiled SQL code stored on the database server. They improve performance, security (by encapsulating logic), and code reusability. In ADO.NET, they are executed using the `SqlCommand` object.

  9. Explain the difference between `SqlDataReader` and `DataSet`.

    • Answer: `SqlDataReader` provides a forward-only, read-only stream of data, ideal for efficient retrieval of large datasets. `DataSet` is an in-memory representation of data, allowing for disconnected operations, updates, and manipulations before committing changes back to the database.

  10. What is connection pooling and how does it improve performance?

    • Answer: Connection pooling reuses database connections instead of creating a new one for each request. This significantly reduces the overhead of establishing connections, improving application performance and responsiveness.

  11. How to handle concurrency issues in ADO.NET?

    • Answer: Concurrency issues are addressed using techniques like optimistic and pessimistic locking, or using row versioning. ADO.NET doesn't directly manage locks, but you can leverage database features and design patterns (like the Unit of Work pattern) to handle concurrency conflicts effectively.

  12. What are some best practices for ADO.NET development?

    • Answer: Use parameterized queries, handle exceptions gracefully, use connection pooling, optimize queries, implement transactions, close connections promptly, and follow appropriate security practices to prevent SQL injection.

  13. Explain the use of DataTables and DataViews in ADO.NET.

    • Answer: `DataTable` represents a single table of data within a `DataSet`. `DataView` provides a customized view of a `DataTable`, allowing filtering, sorting, and other manipulations without modifying the underlying data.

  14. How can you improve the performance of ADO.NET applications?

    • Answer: Optimize SQL queries, use indexes, minimize round trips to the database, utilize connection pooling, use appropriate data access techniques (e.g., `SqlDataReader` for large datasets), and profile your application to identify bottlenecks.

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