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LINQ Interview Questions and Answers

By Umesh Singh
Last update: 22 Apr 2020, 21 Questions
LINQ Interview Questions

LINQ is an abbreviated form of Language -integrated Quer. It is an innovation that is used to bridge the gap between two platforms, namely Visual Studio 2008 and the .NET framework. There is a number of LINQ queries that are used to retrieve data from the data sources. In this, blog, we are providing a collection of LINQ interview questions that will help you in cracking interviews. Traditionally, the queries against data can be expressed in the form of simple strings without supporting IntelliSense. Likewise, users can use the coding patterns for the purpose of transforming data in XML documents, ADO.NET datasets, .NET collections, SQL databases and another format for which LINQ provider is available. We are providing a vast collection of LINQ interview questions, which will help you in achieving success factors.

Most Frequently Asked LINQ Interview Questions

1. What is Select() and SelectMany() in LINQ?

In LINQ, Select() and SelectMany() are projection operators. The use of a Select() operator is to select a value from a collection whereas the use of SelectMany() operator is to select values from a group of collection, i.e. a nested collection.

Example

                                                    

public class PhoneNumber
{
    public string Number { get; set; }
}
public class Person
{
   public IEnumerable PhoneNumbers { get; set; }
   public string Name { get; set; }
}
IEnumerable people = new List();
IEnumerable> phoneLists = people.Select(p => p.PhoneNumbers);
IEnumerable phoneNumbers = people.SelectMany(p => p.PhoneNumbers);
var directory = people .SelectMany(p => p.PhoneNumbers,
(parent, child) => new { parent.Name, child.Number });

2. What is the best way for retrieving single record in LINQ?

Use the First() or FirstOrDefault() command to retrieve single row records in LINQ.

Example

                                                    

var users = (from u in dc.Users where u.UserName == usn select u).FirstOrDefault();

3. What is the difference between Linq and lambda expression?

Following are the difference between LINQ expression and LAMBDA expression

LINQ expression Lambda expression
In order to extend the functionality a query capabilities LINQ expression to the language syntax of C# and Visual Basic. It is a function that is used to create expressions in the form of a tree. With the help of lambda expression, users can write local functions that can be passed as a return value of function calls
4. What is the difference between Single() and First() extension methods in LINQ?
Single() First()
Used to return a single specific element of a query or a default value if no result is found. It is used to return the first element of any query with multiple values.
Used when exactly one element is expected as a result. Used when there are multiple result expectations but you only need the first value.
5. What are the types of LINQ?
LINQ is of five types namely-
  • LINQ to objects
  • LINQ to dataset
  • LINQ to XML (XLINQ)
  • LINQ to entities
  • LINQ to SQL (DLINQ)
6. What is Query and Sequence operators in LINQ?

The query is an expression which is used to recover data from a variety of data sources and query can be expressed in specialized languages.

Three types of actions can be performed on LINQ query namely
  • Get data source
  • Create Query
  • Execution of Query
LINQ does not support sequence operators but it is having the following qualities-
  • Take lambda expression with an index parameter
  • Depend on the properties of sequential rows
  • Depend on the CLR implementation
7. What is Action in LINQ?

Action in LINQ is a delegate type that is used to declare delegate variables without any need to define a custom type. The Action types that represent delegate without return value are the Action types in the System namespace

8. How LINQ is beneficial than stored procedures?

LINQ is beneficial than stored procedure due to-

  • Debugging
  • Type safety
  • Deployment
9. What is the difference between SkipWhile() and Skip() methods in LINQ?
Skip() SkipWhile()
Used to specify the amount (number) of items to skip in a LINQ expression. Used to supply a predicate function on how many numbers to skip.
It will take an integer argument and then simply skips those n numbers from the top of the given IEnumerable It works on a per-line basis. It shall continue to skip if the value returned from the function is true.
Syntax: yourlist.Skip(5) Syntax: yourList.SkipWhile(x => x.marks < 50)
10. What is expression trees in LINQ?

In LINQ, an Expression tree is nothing but expressions systematically organized in a tree-like data structure. Here, each node in an expression tree relates to expression. This is just like an in-memory representation of a lambda expression in which only the actual elements of the query are held and not the result of the query.

11. What are compiled queries in LINQ?

A compiled query in LINQ is actually a cached version of the original query which is used to get similar results. After writing the query, for the first time it is parsed for any errors in LINQ and then converted into its SQL version and finally added as cache.

12. What is PLINQ and how it is different from LINQ?

PLINQ stands for Parallel LINQ which is a query execution engine that drives and manages their operations on the top of the managed environment of .NET.

13. What is LINQ and why it is used?

LINQ is an abbreviated form of Language Integrated Query, which is a part of the language used to used provide seamless and consistent access to a number of data sources such as XML and databases. LINQ is categorized into three varieties namely LINQ (C#), LINQ providers (LINQ to SQL, LINQ to XML and LINQ to Objects), and data sources (collections, SQL and XML)

LINQ is used to make the code readable and compact and it is used to query different types of data sources. likewise, it is familiar language, required less coding, readable code, compile-time safety, IntelliSense support and shaping up of data support.

14. What is the difference between SQL and LINQ?

Following is the difference between SQL and LINQ queries-

1. SQL- The main return type of local variable that holds query in SQL is IQueryable. Moreover, it is a Structured Query Language used for the manipulation of data.

2. LINQ- The main return type of local variable that holds query in LINQ is IEnumerable. Moreover, it translates the query into equivalent SQL queries and sends them for processing to the server.

15. What is the difference between the Take and Skip clause in LINQ?

Following are the difference between TAKE and SKIP clause

1. Take clause- Take clause in LINQ is used to return a specific number of elements.

2. Skip clause- Skip clause is used to skip the specified number of elements in the query and return rest all of the present elements.

16. What is an Anonymous function in LINQ? The anonymous function in LINQ is a function which is used once and for a limited number of times. This function is not bound to an identifier. With the help of anonymous function number of functions are created which have no specified time.
17. What is deferred execution in Linq?

In LINQ, a Deferred Execution basically means that there is a delay in the evaluation of an expression and shall be realized only when the user needs it.

18. What are the difference between Conversion Operator ToDictionary and IEnumerable of LINQ?
ToDictionary IEnumerable
Type of Conversion Operator Also, a kind of Conversion Operator.
It is the instance of Dictionary (k, T) This is an object as a source sequence that is returned to the user via the AsEnumerable operator.
19. What is the difference between N-layer and N-tier architecture?
N-Layer N-Tier
All the layers may reside on the same physical computers(server) while the components in different layers communicate via well-defined interfaces. In this type of architecture, there are at least three separate logical parts, each located on a different physical server.
Communication between layers is explicit and loosely coupled. In this, communication between the tiers is asynchronous to support scalability.
20. What are entity classes in LINQ?

Entity classes are the fundamental building blocks of systems developed on LINQ. In this, the entity classes, which are basically an object wrapper for any database table, have a stereotype of the entity.

21. What are Quantifier Operations in LINQ?

Quantifier operations in LINQ are those which return a Boolean value, i.e. True or False on execution.

Here are the type of Quantifier Operations in LINQ:
  • All()
  • Any()
  • Contains()
Advantages of LINQ
  • Unified data access (Single syntax to learn)
  • Strongly typed (During completion automatically catch errors)
  • IntelliSense (Prompt attributes and syntax)
  • Bind-able result sets
  • Allows debugging through the .NET debugger
  • Type checking at compile time
Disadvantages of LINQ
  • Not suitable to write complex queries like SQL
  • It does not support SQL features such as cached execution
  • Performance degraded if the query is incorrect
  • In order to incorporate changes in query, you need to recompile and redeploy it

The LINQ interview questions that most probably asked during the interview are providing in this blog that will help you in order to achieve the desired goals.