Top LINQ interview questions and answers.

In this article, we are going to cover the top most frequently asked LINQ interview questions and their answers from very basic level to advanced level. These Interview questions will help you to prepare for the interview and as well as enhance your technical skills.

Linq interview questions and Answers.

There is below the list of best LINQ Interview Questions and Their Answers.

Explain What is LINQ?

The abbreviation of LINQ is Language Integrated Query. LINQ is a collection of standard query operators which provide the querying capabilities to the .NET programming languages like c# and vb.net to retrieve data from different sources. It provides a single querying interface for different types of data sources such as collections, XML Docs, Ado.Net DataSet, web services, SQL server, and other databases.

In other words, LINQ is a structured query syntax that is built in vb.net and c# to retrieve the data from different sources. It is the same as SQL. SQL is a structured query language that is used to save and retrieve data from the database.

What are the advantages of LINQ?

There are some advantages of LINQ:

LINQ provides a unified querying syntax to retrieve data from different data sources. So, you don’t need to learn a new query language for each type of data source.
LINQ expressions are strongly typed.
LINQ provides IntelliSense support for generic collections.
LINQ provides support for debugging through the .NET debugger.
LINQ reduces the development time by catching the errors at compile time.

What are the disadvantages of LINQ?

There are some disadvantages of LINQ:

LINQ is not suitable for complex queries.
If you write the LINQ query incorrectly, then the performance will be degraded.
If you will add some changes to your query, then you will have to recompile it and then redeploy it to the server.

What are the different types of LINQ?

There are some below different types of LINQ:

LINQ to Entities.
LINQ to Objects.
LINQ to XML.
LINQ to Dataset.
LINQ to SQL

What are the three main components of LINQ?

There are below three main components of LINQ:

Language Extensions.
Standard Query Operators.
LINQ Providers. 

What is the projection operator in LINQ?

In LINQ, the projection is an operation that converts an object into a new form that keeps only those values or properties which will be used. The type in which these results are converted is defined by the developers. In LINQ, there are two types of projection operators.

Select()
SelectMany()

 How is LINQ beneficial than stored procedure?

 Yes, LINQ is beneficial than stored procedures due to the below reason.

LINQ provides support for debugging through the .NET debugger.
LINQ expressions are strongly typed.
LINQ provides IntelliSense support for generic collections.
It is very easy to deploy a LINQ-based application as compared to a stored procedure based application.

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

As you know, Select() and SelectMany(), both are projection operators. So, the difference is defined below.

Select(): This operator always returns an IEnumerable collection that contains values based on the transformation function. Or we can say that this operator is used when we want to select a value from a collection.

SelectMany(): This operator is used to select values from the multiple collections. Or we can say that this operator is used when we want to select values from a list of lists. 

What is the where clause in LINQ?

In LINQ, the Where clause is used to filter the sequence based on the given criteria. For example, suppose we have a list of books with different prices. And we want only those books which have prices above 100, then we will filter the book list as you do see below in the code line.

Example:

var filteredResult = bookList.Where(b => b.price > 100);

What is the role of DataContext class in LINQ?

The DataContext class acts as a bridge between the SQL Database and LINQ to SQL framework. This class contains information about the methods for connecting to the database. Using this class, we can manipulate the data in the SQL Server database.

What are standard query operators in LINQ?

In LINQ, standard query operators are actually extension methods for the IQueryable<T> and IEnumberable<T> types. The parent classes of these standard query operators are System.Linq.Queryable and System.Linq.Enumerable. There are different functionalities that we can perform using standard query operators like grouping, sorting, filtering, Conversion, Generation, and many others.

Categorize standard query operators based on the functionality in LINQ?

There are different categories of standard query operators based on the functionality in LINQ.

Filtering
Where, OfType

Sorting
OrderBy, OrderByDescending, ThenBy, ThenByDescending, Reverse

Grouping
GroupBy, ToLookup

Join
GroupJoin, Join

Projection
Select, SelectMany

Aggregation
Aggregate, Average, Count, LongCount, Max, Min, Sum

Quantifiers
All, Any, Contains

Elements
ElementAt, ElementAtOrDefault, First, FirstOrDefault, Last, LastOrDefault, Single, SingleOrDefault

Set
Distinct, Except, Intersect, Union

Partitioning
Skip, SkipWhile, Take, TakeWhile

Concatenation
Concat

Equality
SequenceEqual

Generation
DefaultEmpty, Empty, Range, Repeat

Conversion
AsEnumerable, AsQueryable, Cast, ToArray, ToDictionary, ToList

What is the lambda expression in LINQ?

It is the easiest way of defining anonymous methods. At compile time all the lambda expressions are converted into anonymous methods according to lambda expression conversion rules. 

What are the different types of lambda expressions in LINQ?

There are different types of lambda expressions in LINQ:

Statement Lambda
Expression Lambda

What is the difference between Statement Lambda and Expression Lambda?

The difference between the Statement Lambda and Expression Lambda is:

Statement Lambda: It has a statement block on the right side of the lambda operator (“=>”).

Example: a => {return a+a};

Expression Lambda: it has only an expression on the right side of the lambda operator (“=>”)

Example: a => a+a;

What is the difference between Skip() and SkipWhile() extension method in LINQ?

There is the following difference between Skip() and SkipWhile extension method in LINQ:

Skip(): This extension method will take an integer argument and then it will skip the top n (n is the integer argument) numbers from the given data source.

SkipWhile(): This extension method will continue to skip the elements as far as the condition is true. 

How standard query operators are useful in LINQ?

There are the following ways in which the Standard Query Operators are useful.

It provides the facility for grouping.
It provides the facility for computing the average.
It provides the facility of joins based on the matching keys.
It provides the facility of filtration.
It provides the facility of ordering the elements of the collection.
It provides the facility to get Aggregate, Count, LongCount, Max, and Min.

How to retrieve a single row using LINQ?

We can retrieve a single row using the below syntax.

Var singleObj = dbContext.books.Single(b => b.Name == “Book Name”);

We can also retrieve a single record using First() and FirstOrDefault().

Var singleObj = dbContext.books.where(b => b.Name == “Book Name”).FirstOrDefault();

Var singleObj = dbContext.books.where(b => b.Name == “Book Name”).First();

What is the difference between the Single() and First() extension methods in LINQ?

There is the following difference between Single() and First() extension methods in LINQ:

Single(): 

This method is used to get a single specific element of a query. It will get a default value if the result is not found.
This method is used when exactly one element is expected as a result.

First():

This method is used to get the first element of any query with multiple values.
This method is used when there are multiple items but we need only the first value.

What are quantifier operations in LINQ?

In LINQ, these operations return boolean values on the query execution.

What are the Types of Quantifier operations in LINQ

There are different kinds of quantifier operations in LINQ:

All(): It will return the true value of all of the elements in a sequence that satisfies the specified condition.

Any(): It will return the true value if any of the elements in a sequence that satisfies the specified condition.

Contains(): It will return a true value if the sequence contains the specific element.

What is the deferred execution in LINQ?

In deferred execution, the evaluation of an expression is delayed until its realized value is actually required. In other words, when we declare a query, it will not execute it. It will execute the query, when the realized value is executed within the loop like foreach, and for. In this way it helps us to improve the performance and avoid unnecessary execution.

Example:

Var bookList = from obj in books
where obj.Price > 100
Select obj;
//query is executed yet.
for(var obj in bookList) // the query will be executed here.
{
//write code here
}

What is LINQ to Objects?

In LINQ, “LINQ to Objects” provides us the facility to use IEnumerable or IEnumerable<T> collection directory in LINQ queries without the use of any intermediate LINQ provider or API such as LINQ to SQL, or LINQ to XML.

What is LINQ to SQL?

It is part of the ADO.NET technologies. In LINQ to SQL, it converts the LINQ into the SQL object and then forwards it to the database for execution. And when the database returns a response, then the result LINQ to SQL translates it back to the object. Basically, LINQ to SQL manages the relational data as an object.

What is PLINQ?

The abbreviation of PLINQ is Parallel Language Integrated Query. PLINQ is used to execute a query by using multiple processors, and it is a parallel implementation of LINQ. It is a query execution engine that drives and manages its operations on top of the managed environment of .NET.

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