Select records which has no day-off throughout the week in List<T> - C#

Question

I have an Employee class which defined as this:

Employee
{
   public int Id { get; set; }
   public string Name { get; set; }
   public DateTime WorkDate { get; set; }
   public bool isOff { get; set; }
}

This is my class implementation and usage:

List<Employee> workers = new List<Employee>()
{
    new Employee { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/11/2016"), IsOff = false},
    new Employee { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/12/2016"), IsOff = false},
    new Employee { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/13/2016"), IsOff = true},
    new Employee { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/14/2016"), IsOff = false},
    new Employee { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/15/2016"), IsOff = false},
    new Employee { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/16/2016"), IsOff = false},
    new Employee { Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/17/2016"), IsOff = false},
    new Employee { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/11/2016"), IsOff = false},
    new Employee { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/12/2016"), IsOff = false},
    new Employee { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/13/2016"), IsOff = false},
    new Employee { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/14/2016"), IsOff = false},
    new Employee { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/15/2016"), IsOff = false},
    new Employee { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/16/2016"), IsOff = false},
    new Employee { Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/17/2016"), IsOff = false},
};

In the initialization above there is only 1 record that is off:

Id = 1, Name = "Emp 1" and the WorkDate = 4/13/2016

Now how can i get the id of an employee which has no day off throughout the week (from April 11-17)? Which is Id = 2

A LINQ solution is far better but i dont know how to do it.

UPDATED

To avoid confusion of the object Employee i changed it to EmployeeSchedule

class EmployeeSchedule
{
   public int Id { get; set; }
   public string Name { get; set; }
   public DateTime WorkDate { get; set; }
   public bool isOff { get; set; }
}

This is the implementation

List<EmployeeSchedule> workers = new List<EmployeeSchedule>()
{
    new EmployeeSchedule{ Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/11/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/12/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/13/2016"), IsOff = true},
    new EmployeeSchedule{ Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/14/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/15/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/16/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 1, Name = "Emp 1", WorkDate = Convert.ToDateTime("4/17/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/11/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/12/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/13/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/14/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/15/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/16/2016"), IsOff = false},
    new EmployeeSchedule{ Id = 2, Name = "Emp 2", WorkDate = Convert.ToDateTime("4/17/2016"), IsOff = false},
};

The selected answer is still applicable.

Answer 1

Now how can i get the id of an employee which has no day off throughout the week (from April 11-17)? Which is Id = 2

You could use Linq extensions, and achieve this.

var empid = workers.GroupBy(g=> g.Id)           
                   .Where(x=>x.All(e=>!e.IsOff))
                   .Select(x=>x.Key)

Answer 2

That means you need a fromDate, toDate, and you have to find the employees from the list subject to the condition that, WorkDate should be in between fromDate and toDate, and also isOff == false that means has no day off throughout the week So you can use the following snippet :

 DateTime fromDate = new DateTime(2016, 04, 11);
 DateTime toDate = new DateTime(2016, 04, 17);
 var noDayOfList = workers.GroupBy(x=> x.Id)
                          .Where(x =>
                                 x.All(y=> 
                                 y.WorkDate >= fromDate && 
                                 y.WorkDate <= toDate && 
                                 !y.isOff))
                          .Select(z=>z.Key).ToList();