LINQ Interview Questions and Answers (70) - Page 2

NOTE: This is objective type question, Please click question title for correct answer.

    

public static long display()

        {

            var tempval = (from h in objDB.tbl_mvc_login

                           select h).Count ();



            return tempval;

        }

    

public static long display()

        {

            var tempval = (from h in objDB.tbl_mvc_login

                           select h).LongCount ();



            return tempval;

        }

Look carefully to the above methods declared. They both does the same thing but LongCount() has a greater range than Count(). According to MSDN, it has the range from

long.MinValue = -9223372036854775808

long.MaxValue =  9223372036854775807 

which is quite big. Its DotNet Framework type is System.Int64. While count() DotNet Framework type is System.Int32 which has a range from

long.MinValue = -2,147,483,648

long.MaxValue =  2,147,483,647 

So, next time if you want to count something which is quite big then use LongCount() extension method otherwise use Count().


Thanks and Regards
Akiii

public static int display()

        {

            int[] numbersArray = { 1, 2, 3, 4, 5 };

                        

            return numbersArray.Aggregate((x1, x2) => x1 * x2);

        }

output : 120

In the above code, "numbersArray" is an integer array. Here, the first one being the first number or the previous result, and the second one is the second or next number to participate the calculation.

The calculation goes like :-

1 * 1 = 1 (stored in x1)

x1 * 2 = 2 (stored in x1)

x1 * 3 = 6 (stored in x1)

x1 * 4 = 24 (stored in x1)

x1 * 5 = 120 (stored and returned back)

Thanks and Regards
Akiii

FirstOrDefault() = gets the first item that matches a given criteria.

SingleOrDefault() = if you specify this extension method that means you are specifically saying that there can be only one value that matches the criteria. If there are more then 1 value that matches the criteria, throw an exception.



Thanks and Regards
Akiii

• First() - There is at least one result, an exception is thrown if no result is returned.

• Single() - There is exactly 1 result, no more, no less, an exception is thrown if no result is returned.


Thanks and Regards
Akiii

Let us look at the below situation

<?xml version='1.0' encoding='UTF-8'?>

  <Countries>

	<State Name = 'Karnataka'>

		<City Name='Bangalore' />  

                <City Name= 'Guledgudda' />   

                <City Name= 'Hubli' />  

                <City Name= 'Tumkur' />                         

	</State>  

   </Countries>

The challenge is to get the City Names using XDocument class. The below code will help us to do so

string inputXml = @"<?xml version='1.0' encoding='UTF-8'?>

		     <Countries>

			<State Name = 'Karnataka'>

			 <City Name='Bangalore' />  

                         <City Name= 'Guledgudda' />   

                         <City Name= 'Hubli' />  

                         <City Name= 'Tumkur' />                         

			</State>  

		     </Countries>";

XDocument countrySource = XDocument.Parse(inputXml);  



//The query

          

countrySource

.Descendants("State")

.SelectMany(i => i.Elements())

.ToList()

.ForEach(i=>Console.WriteLine((string)i.Attribute("Name")));





//Output

Bangalore

Guledgudda

Hubli

Tumkur

Consider the below input

var input = new string[] { "Apple", "Banana", "Mango", "Apple", "Orange", "Mango", "Strawberry", "Apple" };

The problem is to write a query using LINQ and LAMBDA that will count the nunber of fruits.

Solution

var input = new string[] { "Apple", "Banana", "Mango", "Apple", "Orange", "Mango", "Strawberry", "Apple" };

            

//Using LINQ

(from a in input

 group a by a into g

 select new

 {

   Key = g.Key

   ,Count = g.Count()



 })

 .ToList()

 .ForEach(i => Console.WriteLine("Number of {0} is {1}", i.Key, i.Count));



//Using Lambda

 input

 .GroupBy(g => g)

 .Select(i => new { Key = i.Key, Count = i.Count() })

 .ToList()

 .ForEach(i => Console.WriteLine("Number of {0} is {1}", i.Key, i.Count));

Output

Number of Apple is 3

Number of Banana is 1

Number of Mango is 2

Number of Orange is 1

Number of Strawberry is 1

Consider the below input

var input = new string[] { "Apple", "Banana", "Mango", "Apple", "Orange", "Mango", "Strawberry", "Apple" };

The problem is to write a query using LINQ that will count the number of fruits and will assign back the value to the same array i.e. we should not create another array for storing the computed values.

Solution

var input = new string[] { "Apple", "Banana", "Mango", "Apple", "Orange", "Mango", "Strawberry", "Apple" };

            

input = (from a in input

        group a by a into g

        where g.Count() >= 2

        select g.Key + " ( " + g.Count() + " )").ToArray();

Output

Apple ( 3 )

Mango ( 2 )

DataTable dt = new DataTable();



var maxLength = dt.AsEnumerable()

                  .SelectMany(r => r.ItemArray.OfType<string>())

                  .Max(i => i.Length);

First cast the Datatable to System.Collections.Generic.IEnumerable<T> object by using the AsEnumerable() extension method,then using the SelectMany extension method
to find out the items in the ItemArray whose type is string and finally figuring out the max length of the records.

DataTable dt = new DataTable();



  var maximumColumnsLengths =

                        Enumerable.Range(0, dt.Columns.Count)

                        .Select(col => dt.AsEnumerable()

                        .Select(row => row[col]).OfType<string>()

                        .Max(val => val.Length)).ToList();

I failed to answer this question in my interview session. So I searched the answer for the question and found in MSDN. After my understanding I just wrote a simple program to understand the left outer join in LINQ.

namespace LeftOuterJoin

{    namespace LeftOuterJoin

    {

        class Employee

        {

            public string EmpName { get; set; }

            public int EmpAge { get; set; }

            public string EmpDeptID { get; set; }

        }

        class Department

        {

            public string DeptID { get; set; }

            public string DeptName { get; set; }

        }

        class Program

        {

            public static void Main(string[] args)

            {

                Employee objEmp1 = new Employee { EmpName = "Naga", EmpAge = 29, EmpDeptID = "1" };

                Employee objEmp2 = new Employee { EmpName = "Sundar", EmpAge = 30, EmpDeptID = "2" };

                Employee objEmp3 = new Employee { EmpName = "Siva", EmpAge = 28, EmpDeptID = "3" };

                Employee objEmp4 = new Employee { EmpName = "Shankar", EmpAge = 31, EmpDeptID = "4" };

                Department objDept1 = new Department { DeptID = "1", DeptName = "IT" };

                Department objDept2 = new Department { DeptID = "2", DeptName = "Admin" };

                Department objDept3 = new Department { DeptID = "3", DeptName = "Testing" };

                Department objDept4 = new Department { DeptID = "4", DeptName = "HR" };

                Department objDept5 = new Department { DeptID = "5", DeptName = "Sales" };

                //Creating List of Objects

                List<Employee> employees = new List<Employee> { objEmp1, objEmp2, objEmp3, objEmp4 };

                List<Department> depts = new List<Department> { objDept1, objDept2, objDept3, objDept4, objDept5 };

                //Left Side Department Right side Employee

                var DeptEmpCollection = from dept in depts

                                        join emp in employees on dept.DeptID equals emp.EmpDeptID into de

                                        from Employees in de.DefaultIfEmpty()

                                        select new { dept.DeptName, EmployeesName = (Employees == null ? "--No Employee--" : Employees.EmpName) };

                foreach (var EmpDept in DeptEmpCollection)

                {

                    Console.WriteLine("Dept {0}, EmpName {1}", EmpDept.DeptName, EmpDept.EmployeesName);

                }

                Console.Read();

            }

        }

    }

}

var employee = (from h in contextobject.Employee 

                where h.EmployeeName == "test"

                select h).FirstOrDefault<Employee>();

Thanks and Regards
Akiii

var employeeList = (from h in context.Employee

                                        where h.EmployeeName == "test"

                                        select h).ToList<Employee>();

Thanks and Regards
Akiii

IEnumerable Vrs IQueryable


In Linq, to query data from database and collections we use IEnumerable and IQueryable. IEnumerable is inherited by IQueryable, so it has all features of it and of its capabilities. Both has their own importance to query data and data manipulation.


IEnumerable :-

1. It exists in System.Collection namespace.
2. It can move forward only over collection.
3. It is best to query data from in-memory collections like Array, List, etc.
4. It is suitable for Linq to Objects and Linq To Xml queries.
5. It doesn't support lazy loading, hence not suitable for paging like scenario.

DataContextClasses db= new DataContextClasses();
IEnumerable<Employee>List =dc.Employees.Where(m=>m.Name.StartsWith("a"));
list=list.Take<Employee>(10);


IQueryable :-

1. It exists in System.Linq namespace.
2. It can move forward only over collection.
3. It is best to query data from out-memory like remote database.
4. It is suitable for Linq to Sql queries.
5. It support lazy loading, hence suitable for paging like scenario.

DataContextClasses db= new DataContextClasses();
IQueryable<Employee>List =dc.Employees.Where(m=>m.Name.StartsWith("a"));
list=list.Take<Employee>(10);

1.We can debug LINQ as it is part of .Net, whereas Stored procedure can’t be.

2. Deployment is easy with LINQ as everything compiled into DLL whereas with Stored procedure script is required for deployment.

3. At compile time we can find error, if any in LINQ but it not possible with Stored procedure.

Stored procedure compiles one time and executed every time whereas LINQ compiled everytime , so Stored Procedure is faster as compare to LINQ.

Var is used to declare implicitly typed local variable means it tells compiler to figure out the type of the variable at compile time.
Since, 'var' is anonymous type, hence it is used where we don't know the type of output like joining of two tables.

var q = (from e in tblEmployee
join d in tblDepartment
on e.DeptID equals d.DeptID
select new
{
e.EmpID, e.FirstName, d.DeptName
});

NOTE: This is objective type question, Please click question title for correct answer.

NOTE: This is objective type question, Please click question title for correct answer.

NOTE: This is objective type question, Please click question title for correct answer.