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LINQ Interview Questions

LINQ Interview Questions

The term LINQ stands for Language Integrated Query. It's a Microsoft .NET Framework module that connects native data querying capabilities to .NET languages. It is initially released in 2007 as a significant part of .NET Framework 3.5. It is fully integrated and offers easy data access from in-memory objects, databases, XML documents, and many more.

LINQ integrates queries in C# and Visual Basic through a set of extensions.

Let's have a look at some most frequently asked LINQ Interview questions and their answers. These questions will help you with interviews as well as other exams.

1) What is LINQ?

The word LINQ is the abbreviation of the Language Integrated Query. It's a .NET framework module that connects native data querying capabilities to .net Language. It offers easy data access from in-memory objects, databases, XML documents, and many more.

2) What are the advantages of using LINQ in Dataset?

The advantages of LINQ are as follows -

  • The primary purpose of using LINQ is to retrieve complex query in a dataset.
  • LINQ is used to combine the values from two different data set.
  • It is also used to fetch a unique value from the data set.
  • LINQ gives a more precise way than SQL query of querying the dataset.
  • LINQ also provides more functionality as compared with ADO.NET.

3) What are the different ways to write LINQ query syntax?

There are two common ways to write a LINQ query to data sources.

  • Query syntax or Expression syntax
  • Method syntax or method Extension Syntax

4) What is the Query syntax?

Query syntax is similar to Structured Query Language for the database. It is described within the C# or VB code.


Few important points about Query syntax are as follows.

  • It starts with FROM keyword and ends with SELECT or GROUP BY keyword.
  • It is same as SQL (Structured Query Language) syntax.
  • It uses some different operators like joining, grouping, sorting, filtering operators to construct the desired result.
  • It uses implicitly typed variable to hold the result of the LINQ query.

5) Explain LINQ method syntax and give an example?

The LINQ method syntax or fluent syntax uses some additional methods included in the Enumerable or Queryable static class.

  • Method Syntax is the same as calling extension method.
  • LINQ Method Syntax is also known as fluent syntax because it facilitates a series of extension methods call.
  • Implicitly typed variable can be used to hold the result of the LINQ query


Example: C# Program for Method Syntax


Java Developer
.Net Developer
Mean Stack Developer

6) Define different types of LINQ?

The different types of LINQ are as follows.

  • LINQ to Objects
  • LINQ to DataSet
  • LINQ to Entities

Apart from the above, there is also a LINQ type named PLINQ, which is Microsoft's parallel LINQ.

7) Describe the architecture of LINQ?

LINQ has 3-Layered architecture. The uppermost layer contains the language extensions, and the bottom layer contains the data sources. The data sources are usually object implementing IEnumerable or IQueryable generic interfaces.

LINQ Interview Questions

Except the basic LINQ query and data sources, there is another component called LINQ provider. The functionality of LINQ provider is to convert the LINQ query into a format so that the available data source can understand it.

8) Explain LINQ to SQL?

LINQ to SQL is a part of ADO.NET technologies. It manages the relational data as an object. LINQ to SQL converts the language integrated query in the object to SQL and forward them to the database for execution. When the database responses, the result LINQ to SQL translate them back to objects.

LINQ to SQL supports user-defined functions and stored procedure in the database.

9) Explain LINQ to XML?

LINQ to XML provides the in-built document reform capabilities of the DOM (Document Object Model) and supports LINQ Queries. Using it, we can modify query, navigate, and save the changes of an XML document. It allows us to write queries to retrieve and navigate a collection of elements and attributes. It is quite similar to XPath and XQuery.

10) Differentiate between LINQ and Stored Procedure?

Some significant differences between LINQ and Stored Procedure are as follows -

  • The stored procedure is faster than a LINQ query because they follow a proper (Expected) execution plan.
  • It is easy to avoid run time errors in SQL query than in comparison to a stored procedure.
  • LINQ uses the .NET debugger to allow debugging, which is not in case of stored procedures.
  • LINQ supports multiple databases in contrast to stored procedures.
  • Deployment of LINQ based solution is more comfortable than the deployment of a stored procedure.

11) What is a LinqDataSource control?

If you want to use LINQ in an ASP.NET webpage, then LinqDataSource is an important part of the dataset. It is used to set the properties in the markup text, control, retrieve, and modify data. It can also be used to declaratively bind other ASP.NET controls on a page to a data source. In this manner, it is similar to SQL Datasource and ObjectDataSource controls.

12) Explain LINQ Lambda expression with example?

In LINQ, Lambda expression is a function that has no name. It makes the syntax more comprehensive by making it short and precise. It is equally important as the LINQ query although it is not as readable as LINQ query. The scope of Lambda expression is limited. It can't be reused.


Lambda expression decides the type in compile time. On the left-hand side of the expression, we put an input parameter under a bracket (). The parameter name can be anything. Ahead of the parameter name sign equal to (=) followed by greater one (>) symbol is used to pass the parameter from left to right side. On the right side, the required operation is performed using the input password passes by the left side parameter. The whole syntax is called Lambda expression.

Example: C# program for lambda expression



13) How would you count the elements in a list or collection?

The Count() function is used to count the number of items in the list.


In C#


If we consider the above syntax, we are counting total number of items in the "Num" list using LINQ Count() function.

14) Define API in LINQ?

LINQ queries can be written for the classes that implement IEnumerable or IQueryable interface. The System.Linq namespace provides many classes for interfaces require for LINQ queries.

LINQ queries use some extension methods for such classes that implement IEnumerable or IQueryable interface.

15) What is Expression Tree in LINQ?

Lambda expressions are extensively used in Expression Tree construction. An Expression Tree represents code in a tree-like format, where each node acts as an impression. Expression trees can be converted into compiled code and run it.

In, .NET framework, Expression class is used to create expression tree through the API. Expression Trees API also support assignment and some control flow expression such as conditional blocks, loops, and try-catch blocks. By using the API, we can generate expression trees that are more complex than those that can be created from lambda expressions.

16) What do you understand by DataContext class? How is it related to LINQ?

The DataContext class acts as a passing point for the LINQ to SQL framework. It is the foundation of all accesses mapped over a database connection.

A Datacontext is lightweight and cheap to create. After adding LINQ to SQL classes, empty DataContext classes that are ready to be configured are represented by empty design surface. DataContext class holds information about the methods for connecting to a database. It also manipulates the data in the database. DataContext classes are configured with the connection data that is availed by the first item.

17) What is the basic syntax of a LINQ query in Visual Basic as well as in C#?

In Visual Basic, From keyword is used to start the basic syntax of LINQ query and it ends with Select or Group By keyword. You can use another keyword like Where, Order By, Order By Descending, etc., for performing additional functions like filtering data or generating data in a specific order.

In C#, the basic syntax starts with from keyword and terminates with Select or Group By keyword. We can use another clause like Where, Order By, Order By Descending, etc. For performing activities like filtering data or generating data in a specific order.

18) Elaborate the PLINQ?

The term PLINQ stands for parallel LINQ. It's a parallel implementation of LINQ to objects. It supports parallel programming, and it is so closely related to the task parallel library. It facilitates with some queries to automatically take advantage of multiple processors. PLINQ is capable of increasing the speed of LINQ to Objects queries by using all available cores on the host computer more efficiently.

Syntax of PLINQ

Following is the syntax of using PLINQ to increase the performance of LINQ queries in c#,

C# Code


If you notice the given syntax, I have used Parallel method with LINQ queries to increase performance of LINQ queries.

19) What are the LINQ Standard Query Operators in LINQ?

The standard query operators are the techniques that form the LINQ pattern. These techniques applied on sequences, where a sequence is an object that implements the IEnumerable<T> interface or the IQueryable<T> interface. The standard query operators provide query capabilities for filtering, projection, sorting, aggregation, and more.

LINQ standard query operators have two groups. The one group that operates on IEnumerable<T> type objects and the other operates on IQueryable<T> type objects.

Consider the following syntax

In the above example, the operators where and select are standard query operators.

Here is the brief classification of some Standard Query operators based on their functionality.

Classification Standard Query Operators
Filtering Where, OfType
Sorting OrderBy, ThenBy, Reverse, OrderByDescending, ThenByDescending
Grouping GroupBy, ToLookup
Join GroupJoin, Join
Projection Select, SelectMany
Aggregation Aggregate, Average, Count, LongCount, Max, Min, Sum
Quantifiers All, Any, Contains
Set Distinct, Except, Intersect, Union
Partitioning Skip, SkipWhile, Take, TakeWhile
Concatenation Concat
Equality SequenceEqual
Conversion AsEnumerable, AsQueryable, Cast, ToArray, ToDictionary, ToList

20) List out the main components of LINQ? Tell what is the extension of the file, when LINQ to SQL is used?

Three major components of LINQ are

  • Standard Query Operators
  • Language Extensions
  • LINQ Providers

The extension of the file when LINQ to SQL is used is .dbml.

21) Explain why SELECT clause comes after FROM clause in LINQ?

LINQ requires all the variables to be declared first. The "FROM" clause of LINQ query defines the condition or range to select records so FROM clause must act before SELECT in LINQ query.

22) What are Anonymous Types?

Anonymous types are run-time compiler generated by the compiler. There is no need to specify the name while creating the Anonymous compiler yet we can write properties names and their values. The compiler creates these properties and assigns values to them at runtime.

Anonymous class is helpful in LINQ queries. It saves the intermediate result while performing queries.

There are some restrictions on Anonymous types as well:

  • Anonymous types cannot implement interfaces.
  • Anonymous types can not specify any methods.
  • We cannot define static members.
  • All defined properties must be initialized.
  • We can only define public fields.

23) Explain what are LINQ compiled queries?

There may be a scenario where we repeatedly need to execute a particular query. LINQ allows us to create a query and make it compiled always.

Benefits of Compiled Queries

  • These Queries do not need to compile each time, so the execution of the query is fast.
  • These Queries are compiled once and can be used any number of times.
  • These Queries does need to be recompiled even if the parameter of the query is being changed.


24) What is the difference between First() and FirstOrDefault() selector methods in LINQ?

The First() method always expects at least one element in the result set. If there isn't any element in the result, First() returns an exception. While FirstOrDefault() is compatible with a result set having 0 elements, it does not throw any exception.

25) What is the difference between N-tier and N-layer architecture?

N-Tier and N-Layer are two different concepts. These terms are generally used during the design of the application architecture. N-Tier stands for the actual n system components of your application. On the other hand, N-Layers stands for the internal architecture of your component.

The main advantages of the layered architectural style are as follows.

  • Abstraction
  • Isolation
  • Manageability
  • Performance
  • Reusability
  • Testability

The main advantages of tier architecture styles are as follows.

  • Maintainability
  • Scalability
  • Flexibility
  • Availability

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