def test_ntile(self):
"""
Compute the group for each of the employees across the entire company,
based on how high the salary is for them. There are twelve employees
so it divides evenly into four groups.
"""
qs = Employee.objects.annotate(ntile=Window(
expression=Ntile(num_buckets=4),
order_by=F('salary').desc(),
)).order_by('ntile', '-salary', 'name')
self.assertQuerysetEqual(
qs, [
('Miller', 'Management', 100000, 1),
('Johnson', 'Management', 80000, 1),
('Wilkinson', 'IT', 60000, 1),
('Smith', 'Sales', 55000, 2),
('Brown', 'Sales', 53000, 2),
('Adams', 'Accounting', 50000, 2),
('Jenson', 'Accounting', 45000, 3),
('Jones', 'Accounting', 45000, 3),
('Johnson', 'Marketing', 40000, 3),
('Smith', 'Marketing', 38000, 4),
('Williams', 'Accounting', 37000, 4),
('Moore', 'IT', 34000, 4),
], lambda x: (x.name, x.department, x.salary, x.ntile))
def test_negative_num_buckets_ntile(self):
msg = "num_buckets must be greater than 0"
with self.assertRaisesMessage(ValueError, msg):
Ntile(num_buckets=-1)