Linq Interview Questions Part 1

What is LINQ?
LINQ, or Language INtegrated Query, is a set of classes added to the .NET Framework 3.5. LINQ adds a rich, standardized query syntax to .NET programming languages that allows developers to interact with any type of data.

What are the advantages of using LINQ or Language INtegrated Query?

In any data driven application, you get data either from a Database, or an XML file or from collection classes. Prior to LINQ, working with each data source requires writing a different style of code. Moreover, working with external resources like data bases, XML files involves communicating with that external resource in some syntax specific to that resource. To retrieve data from a database you need to send it a string that contains the SQL query to execute, similarly, to work with an XML document involves specifying an XPath expression in the form of a string. The idea is that using LINQ you can work with disparate data sources using a similar style without having to know a separate syntax for communicating with the data source (e.g., SQL or XPath) and without having to resort to passing opaque strings to external resources.

In any data driven web application or windows application, we use database as a datasource for the application. In order to get data from the database and display it in a web or windows application, we typically do the following.
1. Prepare your SQL Statements.
2. Execute SQL Statements against the database.
3. Retrieve the results.
4. Populate the Business Objects.
5. Display the Data in the Web Form or Windows From.

In order to send a query to the database we must first establish a connection to the database. We then must encode the logic - the SQL query, its parameters, and the parameters' values - into strings that are supplied to the SqlCommand object. And because these inputs are encoded into opaque strings, there is no compile-time error checking and very limited debugging support. For example, if there is a spelling mistake in the SELECT query causing the Customets table name to be misspelled, this typographical error won't show up until runtime when this page is viewed in a web browser. These typographical errors are easy to make as there is no IntelliSense support. When we use LINQ, Visual Studio would display an error message alerting us about the incorrect table name.

Another mismatch between the programming language and the database is that the data returned by the database is transformed for us into objects accessible through the SqlDataReader, but these objects are not strongly-typed objects like we'd like. To get this data into strongly-typed objects we must write code ourselves that enumerates the database results and populates each record into a corresponding object.


LINQ was designed to address all these issues. LINQ also offers a unified syntax for working with data, be it data from a database, an XML file, or a collection of objects. With LINQ you don't need to know the intricacies of SQL, the ins and outs of XPath, or various ways to work with a collection of objects. All you need be familiar with is LINQ's classes and the associated language enhancements centered around LINQ.

In other words, LINQ provides type safety, IntelliSense support, compile-time error checking, and enhanced debugging scenarios when working with different datasources.