Django queryset NOT INTERSECT for 2 models using postgres

Question

I have a Django app, and I am trying to find out Employee that was NOT in Attendance 2017-12-05. I am trying to find out a queryset to accomplish this.

The following are the details of the model, records, and the outcome I am trying to accomplish.

I have 2 models:

class Employee(models.Model):
    fullname = models.CharField(max_length=30, blank=False)    

class Attendance(models.Model):
    CHECKIN = 1
    CHECKOUT = 2
    ATTENDANCE_TYPE_CHOICES = (
        (CHECKIN, "Check In"),
        (CHECKOUT, "Check Out"),
    )
    employee = models.ForeignKey(Employee)
    activity_type = models.IntegerField(choices = ATTENDANCE_TYPE_CHOICES, default=CHECKIN)
    timestamp = models.DateTimeField(auto_now_add=True)

Assuming I have the records below:

Employee
{"id":1, "employee":"michael jackson",
"id":2, "fullname":"mariah carey",
"id":3, "fullname":"taylor swift",
"id":4, "fullname":"selena gomez"}

Attendance
{"id":1, "employee": 1,"activity_type": 1, timestamp: "2017-12-05 09:08",     
"id":2, "employee": 2,"activity_type": 1, timestamp: "2017-12-05 10:13",
"id":3, "employee": 2,"activity_type": 2, timestamp: "2017-12-05 15:13", 
"id":4, "employee": 2,"activity_type": 1, timestamp: "2017-12-05 19:13", 
"id":5, "employee": 3,"activity_type": 1, timestamp: "2017-12-06 08:08"}

This is the intended output I am trying to accomplish:

For the date 2017-12-05, this employee was not in attendance (meaning there was no record in Attendance for 2017-12-05)

{"id":3, "fullname":"taylor swift",
"id":4, "fullname":"selena gomez"}

What is the queryset to list out the employee that is not in attendance on a particular date 2017-12-05 ? I believe its an intersect and doing a NOT with the employee.

Answer 1

You can do this with a simple exclude() query:

from datetime import date

today = date.today()

Employee.objects.exclude(attendance__timestamp__date=today)

This will give you all the employees where there was no attendance recorded for that date.

See this section of the documentation for explanation of how to create the lookup.