from __future__ import absolute_import, unicode_literals 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': 'Example Inc.', 'num_employees': 2300 }, { 'num_chairs': 5, 'name': 'Foobar Ltd.', 'num_employees': 3 }, { 'num_chairs': 34, 'name': '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': 'Example Inc.', 'num_employees': 2300 }, { 'num_chairs': 9, 'name': 'Foobar Ltd.', 'num_employees': 3 }, { 'num_chairs': 96, 'name': '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': 'Example Inc.', 'num_employees': 2300 }, { 'num_chairs': 15, 'name': 'Foobar Ltd.', 'num_employees': 3 }, { 'num_chairs': 1088, 'name': '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)