Top 12 LINQ Interview Questions & Answers

Top 12 LINQ Interview Questions & Answers

Q1. WHAT IS LINQ ?

ANS :
1. LINQ is known as language integrated query and it is introduced in .NET 3.5 and Visual Studio 2008. 

2. It is used to generate queries to perform operations on database tables. 

3. Previously linq is not there then at that time we need to learn different types of query language to access such type of data like SQL, XML, etc. And also we cannot create a query using C# language

4. In C#, LINQ is present in System.Linq namespace. It provides different type of classes and methods which supports LINQ queries.

Q2. WHAT ARE THE TYPES OF LINQ ?

ANS : 

 1. LINQ to Objects

 2. LINQ to XML

 3. LINQ to Dataset

 4. LINQ to SQL

 5. LINQ to Entities

Q3. WHY LINQ IS REQUIRED ?

ANS : The main purpose behind creating LINQ is, before C# we use for loop, foreach loop to traverse a collection to find a specific object, but the disadvantage of using these methods for finding an object is you need to write a large sum of code to find an object which is more time-consuming and make your program less readable. So to overcome these problems LINQ introduced. Which perform the same operation in a few numbers of lines and make your code more readable and also you can use the same code in other programs.

Q5. WHAT IS THE ROLE OF DATA CONTEXT CLASSES IN LINQ ?

ANS : DataContext class acts as a bridge between SQL Server database and the LINQ to SQL. For accessing the database and also for changing the data in the database, it contains connections string and the functions. Essentially a DataContext class help us to Create connection to database and help to perform operations on database

Q6. EXPLAIN HOW LINQ IS USEFUL THAN STORED PROCEDURE  ?

ANS.:  

1.  It is difficult to debug a stored procedure but as LINQ is part of.NET, visual studio debugger can be used to debug the queries

2. For stored procedure, additional script should be provided but with LINQ everything gets compiled into single DLL hence deployment becomes easy

3. LINQ is type safe, so queries errors are type checked at compile time.

Q7. WHEN TO USE FIRST() AND WHEN TO USE FIRSTORDEFAULT() IN LINQ ?

ANS : 

1. Use First() when you know at least one element is there. If no element is there then it will throw an exception.

2. Use FirstOrDefault() when you know at least one element is there. If no element is there then it will assign OR return null instead of giving an exception.

Q8. WHAT IS THE USE OF SYSTEM.LINQ ?

ANS : SYSTEM.LINQ is used to provide the functionality to work with LINQ to Entities.

Q9. EXPLAIN HOW YOU CAN RETRIEVE A SINGLE ROW WITH LINQ ?

ANS : 

Public User GetUser (string userName)

{

DBNameDataContext myDB = new DBNameDataContext ( ) ;

User user = myDB. Users. Single ( u, u.UserName => userName );

Return user;

}

Q10. WHAT IS LINQ TO ENTITIES ?

ANS : 

1. Linq to Entities means writing LINQ queries over entity framework objects. 

2. Just with the help of entity framework we can fetch the table model and we will call these objects as Entities and we can perform operations on that like select, insert etc

Q11. HOW WE CAN CREATE QUERY IN LINQ WITH THE HELP OF LINQ TO ENTITIES ?

ANS : 

1. We can use linq to Entities in C#

2. LINQ to Entities used in entity framework to access the data from the underlying database.

3. Example :- 

-> First you have to create DbContext class. The DbContext class includes dbset property of object and save every objects of the particular class.

-> And just we will use that DbContext class in another class in which we will write the entity to perform some operations on the table of database.
-> Below example code is there :-

var ctx = new SchoolDBEntities();
var student = ctx.Students.Find(1);

SELECT 
[Extent1].[StudentID] AS [StudentID], 
[Extent1].[StudentName] AS [StudentName], 
[Extent1].[StandardId] AS [StandardId]
FROM [dbo].[Student] AS [Extent1]
WHERE [Extent1].[StudentId] = @p0',N'@p0 int',@p0=1
go

using (var ctx = new SchoolDBEntities())
{    
    var student = (from s in ctx.Students
                where s.StudentName == "Bill"
                select s).FirstOrDefault<Student>();
}

Q12. WHY WE USE LINQ AND WHAT ARE THE ADVANTAGES OF THAT ?

ANS : 

1. The main purpose behind creating LINQ is, before C# we use for loop, foreach loop to traverse a collection to find a specific object, but the disadvantage of using these methods for finding an object is you need to write a large sum of code to find an object which is more time-consuming and make your program less readable. So to overcome these problems LINQ introduced. Which perform the same operation in a few numbers of lines and make your code more readable and also you can use the same code in other programs.

2. It also provides full type checking at compile time, it helps us to detect the error at the runtime

3. With the help of LINQ you can easily work with any type of data source like XML, SQL, Entities, objects, etc.

4. LINQ supports filtering, sorting, ordering, grouping.