Compare 2 list objects

You could try something like this:

      List<Employee> oldEmp = new List<Employee>();
      List<Employee> newEmp = new List<Employee>();
      oldEmp.Add(new Employee
      {
        EmployeeId=1,
        Description="A",
        Summary = "1"
      });
      newEmp.Add(new Employee
      {
        EmployeeId = 1,
        Description = "A",
        Summary = "1"
      });
      oldEmp.Add(new Employee
      {
        EmployeeId = 2,
        Description = "B",
        Summary = "1"
      });
      newEmp.Add(new Employee
      {
        EmployeeId = 2,
        Description = "B",
        Summary = "2"
      });
      oldEmp.Add(new Employee
      {
        EmployeeId = 3,
        Description = "C",
        Summary = "1"
      });
      newEmp.Add(new Employee
      {
        EmployeeId = 3,
        Description = "C",
        Summary = "1"
      });

      List<Employee> difference = oldEmp.Where(x => !newEmp.Any(x1 => x1.Summary.Equals(x.Summary)))
            .Union(newEmp.Where(x => !oldEmp.Any(x1 => x1.Summary.Equals(x.Summary)))).ToList();