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from django.core.exceptions import FieldError
from django.db.models import F
from django.test import TestCase
from models import Company, Employee
class ExpressionsTests(TestCase):
def test_filter(self):
Company.objects.create(
name="Example Inc.", num_employees=2300, num_chairs=5,
ceo=Employee.objects.create(firstname="Joe", lastname="Smith")
)
Company.objects.create(
name="Foobar Ltd.", num_employees=3, num_chairs=4,
ceo=Employee.objects.create(firstname="Frank", lastname="Meyer")
)
Company.objects.create(
name="Test GmbH", num_employees=32, num_chairs=1,
ceo=Employee.objects.create(firstname="Max", lastname="Mustermann")
)
company_query = Company.objects.values(
"name", "num_employees", "num_chairs"
).order_by(
"name", "num_employees", "num_chairs"
)
# We can filter for companies where the number of employees is greater
# than the number of chairs.
self.assertQuerysetEqual(
company_query.filter(num_employees__gt=F("num_chairs")), [
{
"num_chairs": 5,
"name": "Example Inc.",
"num_employees": 2300,
},
{
"num_chairs": 1,
"name": "Test GmbH",
"num_employees": 32
},
],
lambda o: o
)
# We can set one field to have the value of another field
# Make sure we have enough chairs
company_query.update(num_chairs=F("num_employees"))
self.assertQuerysetEqual(
company_query, [
{
"num_chairs": 2300,
"name": "Example Inc.",
"num_employees": 2300
},
{
"num_chairs": 3,
"name": "Foobar Ltd.",
"num_employees": 3
},
{
"num_chairs": 32,
"name": "Test GmbH",
"num_employees": 32
}
],
lambda o: o
)
# We can perform arithmetic operations in expressions
# Make sure we have 2 spare chairs
company_query.update(num_chairs=F("num_employees")+2)
self.assertQuerysetEqual(
company_query, [
{
'num_chairs': 2302,
'name': u'Example Inc.',
'num_employees': 2300
},
{
'num_chairs': 5,
'name': u'Foobar Ltd.',
'num_employees': 3
},
{
'num_chairs': 34,
'name': u'Test GmbH',
'num_employees': 32
}
],
lambda o: o,
)
# Law of order of operations is followed
company_query.update(
num_chairs=F('num_employees') + 2 * F('num_employees')
)
self.assertQuerysetEqual(
company_query, [
{
'num_chairs': 6900,
'name': u'Example Inc.',
'num_employees': 2300
},
{
'num_chairs': 9,
'name': u'Foobar Ltd.',
'num_employees': 3
},
{
'num_chairs': 96,
'name': u'Test GmbH',
'num_employees': 32
}
],
lambda o: o,
)
# Law of order of operations can be overridden by parentheses
company_query.update(
num_chairs=((F('num_employees') + 2) * F('num_employees'))
)
self.assertQuerysetEqual(
company_query, [
{
'num_chairs': 5294600,
'name': u'Example Inc.',
'num_employees': 2300
},
{
'num_chairs': 15,
'name': u'Foobar Ltd.',
'num_employees': 3
},
{
'num_chairs': 1088,
'name': u'Test GmbH',
'num_employees': 32
}
],
lambda o: o,
)
# The relation of a foreign key can become copied over to an other
# foreign key.
self.assertEqual(
Company.objects.update(point_of_contact=F('ceo')),
3
)
self.assertQuerysetEqual(
Company.objects.all(), [
"Joe Smith",
"Frank Meyer",
"Max Mustermann",
],
lambda c: unicode(c.point_of_contact),
)
c = Company.objects.all()[0]
c.point_of_contact = Employee.objects.create(firstname="Guido", lastname="van Rossum")
c.save()
# F Expressions can also span joins
self.assertQuerysetEqual(
Company.objects.filter(ceo__firstname=F("point_of_contact__firstname")), [
"Foobar Ltd.",
"Test GmbH",
],
lambda c: c.name
)
Company.objects.exclude(
ceo__firstname=F("point_of_contact__firstname")
).update(name="foo")
self.assertEqual(
Company.objects.exclude(
ceo__firstname=F('point_of_contact__firstname')
).get().name,
"foo",
)
self.assertRaises(FieldError,
lambda: Company.objects.exclude(
ceo__firstname=F('point_of_contact__firstname')
).update(name=F('point_of_contact__lastname'))
)
# F expressions can be used to update attributes on single objects
test_gmbh = Company.objects.get(name="Test GmbH")
self.assertEqual(test_gmbh.num_employees, 32)
test_gmbh.num_employees = F("num_employees") + 4
test_gmbh.save()
test_gmbh = Company.objects.get(pk=test_gmbh.pk)
self.assertEqual(test_gmbh.num_employees, 36)
# F expressions cannot be used to update attributes which are foreign
# keys, or attributes which involve joins.
test_gmbh.point_of_contact = None
test_gmbh.save()
self.assertTrue(test_gmbh.point_of_contact is None)
def test():
test_gmbh.point_of_contact = F("ceo")
self.assertRaises(ValueError, test)
test_gmbh.point_of_contact = test_gmbh.ceo
test_gmbh.save()
test_gmbh.name = F("ceo__last_name")
self.assertRaises(FieldError, test_gmbh.save)
# F expressions cannot be used to update attributes on objects which do
# not yet exist in the database
acme = Company(
name="The Acme Widget Co.", num_employees=12, num_chairs=5,
ceo=test_gmbh.ceo
)
acme.num_employees = F("num_employees") + 16
self.assertRaises(TypeError, acme.save)
|
