Top 37 LINQ Interview Questions And Answers

Question 1

Explain what is LINQ? Why is it required?

Accepted Answer

**Language Integrated Query** or **LINQ** is the collection of standard query operators which provides query facilities into.NET framework language like C#, VB.NET. LINQ is required as it bridges the gap between the world of data and the world of objects.

Question 2

What are the _types_ of LINQ?

Accepted Answer

*   LINQ to Objects
*   LINQ to XML
*   LINQ to Dataset
*   LINQ to SQL
*   LINQ to Entities

Question 3

Filter out the first 3 even numbers from the list using LINQ

Accepted Answer

```csharp
var evenNumbers = List
   .Where(x => x % 2 ==0)
   .Take(3)
```

Question 4

Explain what is the purpose of LINQ providers in LINQ?

Accepted Answer

LINQ providers are set of classes that take an LINQ query which generates method that executes an equivalent query against a particular data source.

Question 5

What is _Anonymous function_?

Accepted Answer

An Anonymous function is a special function which does not have any name. We just define their parameters and define the code into the curly braces.

Consider:
```csharp
delegate int func(int a, int b);
static void Main(string[] args)
{
    func f1 = delegate(int a, int b)
    {
        return a + b;
    };
 
    Console.WriteLine(f1(1, 2));
}
```

Question 6

In LINQ how will you find the index of the element using `where()` with Lambda Expressions?

Accepted Answer

In order to find the index of the element use the overloaded version of `where()` with the lambda expression:

```csharp
where(( i, ix ) => i == ix);
```

Question 7

Explain how LINQ is useful than Stored Procedures?

Accepted Answer

*   **Debugging:** 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
*   **Deployment:** For stored procedure, additional script should be provided but with LINQ everything gets compiled into single DLL hence deployment becomes easy
*   **Type Safety:** LINQ is type safe, so queries errors are type checked at compile time

Question 8

Explain what is _LINQ to Objects_?

Accepted Answer

When LINQ queries any `IEnumerable(<T>)` collection or IEnumerable directly without the use of an intermediate LINQ provider or API such as LINQ to SQL or LINQ to XML is referred as **LINQ to Objects**.

Question 9

List out the three main components of LINQ?

Accepted Answer

Three main components of LINQ are

*   Standard Query Operators
*   Language Extensions
*   LINQ Providers

Question 10

What are _Anonymous Types_?

Accepted Answer

Anonymous types are types that are generated by compiler at run time. When we create a anonymous type we do not specify a name. We just write properties names and their values. Compiler at runtime create these properties and assign values to them.

```csharp
var k = new { FirstProperty = "value1", SecondProperty = "value2" };
Console.WriteLine(k.FirstProperty);
```

Anonymous class is useful in LINQ queries to save our intermediate results.

There are some restrictions on Anonymous types as well:

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

Top 37 LINQ Interview Questions

Explain what is LINQ? Why is it required?

What are the types of LINQ?

What are Anonymous Types?

Mention what is the role of `DataContext` classes in LINQ?

What are Extension Methods?

Explain why `SELECT` clause comes after `FROM` clause in LINQ?

Explain what is LINQ to Objects?

Explain what is the purpose of LINQ providers in LINQ?

Explain how LINQ is useful than Stored Procedures?

In LINQ how will you find the index of the element using `where()` with Lambda Expressions?

What is Anonymous function?

List out the three main components of LINQ?

What is LINQ in C#?

What is the difference between `First()` and `Take(1)`?

Explain what are LINQ compiled queries?

Explain what is Lambda Expressions in LINQ?

What is Expression Trees and how they used in LINQ?

Could you compare Entity Framework vs LINQ to SQL vs ADO.NET with stored procedures?

When trying to decide between using the Entity Framework and LINQ to SQL as an ORM, what's the difference?

Could you explian what is the exact deference between deferred execution and Lazy evaluation in C#?

Define what is `let` clause?

Explain how standard query operators useful in LINQ?

When to use `First()` and when to use `FirstOrDefault()` with LINQ?

Explain what is the difference between `Skip()` and `SkipWhile()` extension method?

Explain the difference between `Select` and `Where`

Name some advantages of LINQ over Stored Procedures

When should I use a `CompiledQuery`?

What is an equivalent to the `let` keyword in chained LINQ extension method calls?

Can you provide a concise distinction between anonymous method and lambda expressions?

What is the difference between returning `IQueryable<T>` vs. `IEnumerable<T>`?

What are the benefits of a Deferred Execution in LINQ?

Why use `AsEnumerable()` rather than casting to `IEnumerable<T>`?

What is the difference between `Select` and `SelectMany`?

Name some disadvantages of LINQ over Stored Procedures

Filter out the first 3 even numbers from the list using LINQ

Using LINQ to remove elements from a `List<T>`

Get the indexes of top `n` items where item `value = true`

Top 37 LINQ Interview Questions

Explain what is LINQ? Why is it required?

What are the types of LINQ?

What are Anonymous Types?

Mention what is the role of DataContext classes in LINQ?

What are Extension Methods?

Explain why SELECT clause comes after FROM clause in LINQ?

Explain what is LINQ to Objects?

Explain what is the purpose of LINQ providers in LINQ?

Explain how LINQ is useful than Stored Procedures?

In LINQ how will you find the index of the element using where() with Lambda Expressions?

What is Anonymous function?

List out the three main components of LINQ?

What is LINQ in C#?

What is the difference between First() and Take(1)?

Explain what are LINQ compiled queries?

Explain what is Lambda Expressions in LINQ?

What is Expression Trees and how they used in LINQ?

Could you compare Entity Framework vs LINQ to SQL vs ADO.NET with stored procedures?

When trying to decide between using the Entity Framework and LINQ to SQL as an ORM, what's the difference?

Could you explian what is the exact deference between deferred execution and Lazy evaluation in C#?

Define what is let clause?

Explain how standard query operators useful in LINQ?

When to use First() and when to use FirstOrDefault() with LINQ?

Explain what is the difference between Skip() and SkipWhile() extension method?

Explain the difference between Select and Where

Name some advantages of LINQ over Stored Procedures

When should I use a CompiledQuery?

What is an equivalent to the let keyword in chained LINQ extension method calls?

Can you provide a concise distinction between anonymous method and lambda expressions?

What is the difference between returning IQueryable<T> vs. IEnumerable<T>?

What are the benefits of a Deferred Execution in LINQ?

Why use AsEnumerable() rather than casting to IEnumerable<T>?

What is the difference between Select and SelectMany?

Name some disadvantages of LINQ over Stored Procedures

Filter out the first 3 even numbers from the list using LINQ

Using LINQ to remove elements from a List<T>

Get the indexes of top n items where item value = true

Mention what is the role of `DataContext` classes in LINQ?

Explain why `SELECT` clause comes after `FROM` clause in LINQ?

In LINQ how will you find the index of the element using `where()` with Lambda Expressions?

What is the difference between `First()` and `Take(1)`?

Define what is `let` clause?

When to use `First()` and when to use `FirstOrDefault()` with LINQ?

Explain what is the difference between `Skip()` and `SkipWhile()` extension method?

Explain the difference between `Select` and `Where`

When should I use a `CompiledQuery`?

What is an equivalent to the `let` keyword in chained LINQ extension method calls?

What is the difference between returning `IQueryable<T>` vs. `IEnumerable<T>`?

Why use `AsEnumerable()` rather than casting to `IEnumerable<T>`?

What is the difference between `Select` and `SelectMany`?

Using LINQ to remove elements from a `List<T>`

Get the indexes of top `n` items where item `value = true`