LINQ Interview Questions

1. What is Language Integrated Query (LINQ)?

LINQ is a programming model that is the composition of general-purpose standard query operators that allow you to work with data, regardless of the data source in any .NET based programming language. It is the name given to a set of technologies based on the integration of query capabilities into any .NET language.

2. What are LINQ query expressions?

A LINQ query, also known as a query expression, consists of a combination of query clauses that identify the data sources for the query. It includes instructions for sorting, filtering, grouping, or joining to apply to the source data. The LINQ query expressions syntax is similar to the SQL syntax. It specifies what information should be retrieved from the data source.

3. Write the basic steps to execute a LINQ query.

The following are the three basic steps to execute a LINQ query:

• Obtain the data source (The data source can be either an SQL database or an XML file)
• Create a query
• Execute the query

4. Write the basic syntax of a LINQ query in Visual Basic as well as in C#.

In Visual Basic, the basic syntax of a LINQ query starts with the From clause and ends with the Select or Group By clause. In addition, you can use the Where, Order By, and Order By Descending clauses to perform additional functions, such as filtering data and generating the data in a specific order.

In C#, the basic syntax of a LINQ query starts with the From clause and ends with the Select or group by clause. In addition, you can use the where, orderby, and Orderby descending clauses to perform additional functions, such as filtering data and generating the data in a specific order.

5. In which statement the LINQ query is executed?

A LINQ query is executed in the For Each statement in Visual Basic and in the foreach statement in C#.

6. In LINQ, lambda expressions underlie many of the standard query operators. Is it True or False?

It is true.

7. What is PLINQ?

PLINQ stands for Parallel Language Integrated Query. It is the parallel implementation of LINQ, in which a query can be executed by using multiple processors. PLINQ ensures the scalability of software on parallel processors in the execution environment. It is used where data grows rapidly, such as in telecom industry or where data is heterogeneous.

PLINQ also supports all the operators of LINQ. In addition, you can query 'collections by using PLINQ. It can also run several LINQ queries simultaneously and makes use of the processors on the system. Apart from this, PLINQ uses parallel execution, which helps in running the queries quickly. Parallel execution provides a major performance improvement to PLINQ over certain types of legacy code, which takes too much time to execute.

8. What are the different Visual Basic features that support LINQ?

Visual Basic includes the following features that support LINQ:

• Anonymous types - Enables you to create a new type based on a query result.
• Implicitly typed variables - Enables the compiler to infer and assign a type when you declare and initialize a variable.
• Extension method - Enables you to extend an existing type with your own methods without modifying the type itself.

9. What is the function of the DISTINCT clause in a LINQ query?

The DISTINCT clause returns the result set without the duplicate values.

10. What is the DataContext class and how is it related to LINQ?

After you add a LINQ to SQL Classes item to a project and open the O/R Designer, the empty design surface represents an empty DataContext class ready to be configured. The DataContext class is a LINQ to SQL class that acts as a conduit between a SQL Server database and the LINQ to SQL entity classes mapped to that database. This class contains the connection string information and the methods for connecting to a database and manipulating the data in the database. It is configured with connection information provided by the first item that is dragged onto the design surface.

11. What is the difference between the Take and Skip clauses?

The Take clause returns a specified number of elements. For example, you can use the Take clause to return two values from an array of numbers. The Skip clause skips the specified number of elements in the query and returns the rest. For example, you can use the Skip clause to skip the first four strings in an array of strings and return the remaining array of string.

12. What is Object Relational Designer (0/R Designer)?

The 0/R Designer provides a visual design surface to create LINQ to SQL entity classes and associations (relationships) that are based on objects in a database.

13. Which interface implements the standard query operators in LINQ?

The standard query operators implement the IEnumerable<T> or the IQueryable<T> interface in C# and the IEnumerable(Of T) or the IQueryable(Of T) interface in Visual Basic.

14. What are standard query operators in LINQ?

The standard query operators in LINQ are the extension methods that form the LINQ pattern. These operators form an API that enables querying of any .NET array or collection. It operates on sequences and allows you to perform operations, such as determining if a value exists in the sequence and performing an aggregated function, such as a summation over a sequence.

15. On what parameter does the GroupBy clause group the data?

The GroupBy clause groups the elements that share a common attribute.

16. What is a LinqDataSource control?

The LinqDataSource control enables you to use LINQ. in an ASP.NET Web page by setting the properties in the markup text. You can use the control retrieve or modify data. It is similar to the SqIDataSource and ObjectDataSource controls in the sense that it can be used to declaratively bind other ASP.NET controls on a page to a data source. The difference is that instead of binding directly to a database or to a generic class, the LinqDataSource control is designed to bind a LINQ enabled data model.

17. How can you open the O/R Designer?

You can open the O/R Designer by adding a new LINQ to SQL Classes item to a project.

18. The standard query operators are themselves a set of extension methods that provide the LINQ query functionality for any type that implements the IEnumerable<T> interface in Visual Basic. Is it True or False?

False, as it implements the IEnumerable(T) interface in Visual Basic and the IEnumerable<T> interface is implemented in C#.

19. What are lambda expressions in LINQ?

A lambda expression is a function without a name that calculates and returns a single value. All lambda expressions use the lambda operator =>, which read as goes to. The left side of the lambda operator specifies the input parameters and the right side holds the expression or statement block.

20. Before you query a DataSet object by using LINQ to DataSet, you must first populate the dataset How can you do this?

You can load the data into the dataset by using different methods, such as:

• Using the DataAdapter class
• Using LINQ to SQL

21. What are the different implementations of LINQ?

The different implementations of LINQ are:

• LINQ to SQL - Refers to a component of.NET Framework version 3.5 that provides a run-time infrastructure to manage relational data as objects.
• LINQ to DataSet - Refers to a component that makes it easier and faster to query over data cached in a DataSet object.
• LINQ to XML - Provides an in-memory XML programming interface.
• LINQ to Objects - Refers to the use of LINQ queries with any IEnumerable or IEnumerable(T) collection directly, without the use of an intermediate LINQ provider or API, such as LINQ to SQL or LINQ to XML.

22. Which command-line tool generates code and mapping for the LINQ to SQL component of .NET Framework?

The SqlMetal.exe command-line tool generates code and map the LINQ to SQL component.

23. Name the control that exposes the LINQ features to Web developers through the ASP.NET data-source control architecture.

The LinqDataSource control exposes the LINQ features to Web developers through the ASP.NET data-source control architecture.

24. What is the difference between the Select clause and SelectMany() method in LINQ?

Both the Select clause and SelectMany() method are used to produce a result value from a source of values. The difference lies in the result set. The Select clause is used to produce one result value for every source value. The result value is a collection that has the same number of elements from the query. In contrast, the SelectMany() method produces a single result that contains a concatenated collection from the query.

25. Which extension method do you need to run a parallel query in PLINQ?

The AsParallel extension method is required to run a parallel query in PLINQ.