C# Interview Questions -6

Question Can you change the value of a variable while debugging a C# application?
Answer: Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.

Question Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources).

Question What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET?

Answer: SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix, but it’s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.
Question What’s the role of the DataReader class in ADO.NET connections?
Answer: It returns a read-only dataset from the data source when the command is executed.

Question What is the wildcard character in SQL?
Answer: Let’s say you want to query database with LIKE for all employees whose name starts with La. The wildcard character is %, the proper query with LIKE would involve ‘La%’.

Question Explain ACID rule of thumb for transactions. Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after).

Question What connections does Microsoft SQL Server support?

Answer: Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).

Question Which one is trusted and which one is untrusted?
Answer: Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.

Question Why would you use untrusted verificaion?
Answer: Web Services might use it, as well as non-Windows applications.

Question What does the parameter Initial Catalog define inside Connection String? The database name to connect to.

Question What’s the data provider name to connect to Access database?
Answer: Microsoft.Access.

Question What does Dispose method do with the connection object?
Answer: Deletes it from the memory.

Question What is a pre-requisite for connection pooling?
Answer: Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings.