Linq- Projection Operators (Select, SelectMany)

The following 2 standard LINQ query operators belong to Projection Operators category.
Select, SelectMany.

Projection Operators (Select & SelectMany) are used to transform the results of a query.

Select clause in SQL allows to specify what columns we want to retrieve.

In a similar fashion LINQ SELECT standard query operator allows us to specify what properties we want to retrieve. It also allows us to perform calculations.

Example 1: Retrieves just the EmployeeID property of all employees

IEnumerable<int> employeeIds = Employee.GetAllEmployees()

    .Select(emp => emp.EmployeeID);

Example 2: Projects FirstName & Gender properties of all employees into anonymous type.

var result = Employee.GetAllEmployees().Select(emp => new

                    {

                        FirstName = emp.FirstName,

                        Gender = emp.Gender

                    });

foreach (var v in result)

{

    Console.WriteLine(v.FirstName + " - " + v.Gender);

}

  

Example 3: Computes FullName and MonthlySalay of all employees and projects these 2 new computed properties into anonymous type.

var result = Employee.GetAllEmployees().Select(emp => new

{

    FullName = emp.FirstName + " " + emp.LastName,

    MonthlySalary = emp.AnnualSalary / 12

});

foreach (var v in result)

{

    Console.WriteLine(v.FullName + " - " + v.MonthlySalary);

}

Example 4: Give 10% bonus to all employees whose annual salary is greater than 50000 and project all such employee's FirstName, AnnualSalay and Bonus into anonymous type.

var result = Employee.GetAllEmployees()

                .Where(emp => emp.AnnualSalary > 50000)

                .Select(emp => new

                 {

                    Name = emp.FirstName,

                    Salary = emp.AnnualSalary,

                    Bonus = emp.AnnualSalary * .1

                 });

foreach (var v in result)

{

    Console.WriteLine(v.Name + " : " + v.Salary + " - " + v.Bonus);

}

Posted in: LINQ