133 lines
5.3 KiB
Python
133 lines
5.3 KiB
Python
"""
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Tests for F() query expression syntax.
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"""
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from django.db import models
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class Employee(models.Model):
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firstname = models.CharField(max_length=50)
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lastname = models.CharField(max_length=50)
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def __unicode__(self):
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return u'%s %s' % (self.firstname, self.lastname)
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class Company(models.Model):
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name = models.CharField(max_length=100)
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num_employees = models.PositiveIntegerField()
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num_chairs = models.PositiveIntegerField()
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ceo = models.ForeignKey(
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Employee,
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related_name='company_ceo_set')
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point_of_contact = models.ForeignKey(
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Employee,
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related_name='company_point_of_contact_set',
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null=True)
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def __unicode__(self):
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return self.name
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__test__ = {'API_TESTS': """
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>>> from django.db.models import F
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>>> Company(name='Example Inc.', num_employees=2300, num_chairs=5,
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... ceo=Employee.objects.create(firstname='Joe', lastname='Smith')).save()
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>>> Company(name='Foobar Ltd.', num_employees=3, num_chairs=3,
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... ceo=Employee.objects.create(firstname='Frank', lastname='Meyer')).save()
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>>> Company(name='Test GmbH', num_employees=32, num_chairs=1,
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... ceo=Employee.objects.create(firstname='Max', lastname='Mustermann')).save()
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>>> company_query = Company.objects.values('name','num_employees','num_chairs').order_by('name','num_employees','num_chairs')
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# We can filter for companies where the number of employees is greater than the
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# number of chairs.
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>>> company_query.filter(num_employees__gt=F('num_chairs'))
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[{'num_chairs': 5, 'name': u'Example Inc.', 'num_employees': 2300}, {'num_chairs': 1, 'name': u'Test GmbH', 'num_employees': 32}]
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# We can set one field to have the value of another field
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# Make sure we have enough chairs
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>>> _ = company_query.update(num_chairs=F('num_employees'))
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>>> company_query
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[{'num_chairs': 2300, 'name': u'Example Inc.', 'num_employees': 2300}, {'num_chairs': 3, 'name': u'Foobar Ltd.', 'num_employees': 3}, {'num_chairs': 32, 'name': u'Test GmbH', 'num_employees': 32}]
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# We can perform arithmetic operations in expressions
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# Make sure we have 2 spare chairs
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>>> _ =company_query.update(num_chairs=F('num_employees')+2)
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>>> company_query
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[{'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}]
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# Law of order of operations is followed
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>>> _ =company_query.update(num_chairs=F('num_employees') + 2 * F('num_employees'))
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>>> company_query
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[{'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}]
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# Law of order of operations can be overridden by parentheses
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>>> _ =company_query.update(num_chairs=((F('num_employees') + 2) * F('num_employees')))
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>>> company_query
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[{'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}]
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# The relation of a foreign key can become copied over to an other foreign key.
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>>> Company.objects.update(point_of_contact=F('ceo'))
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3
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>>> [c.point_of_contact for c in Company.objects.all()]
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[<Employee: Joe Smith>, <Employee: Frank Meyer>, <Employee: Max Mustermann>]
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>>> c = Company.objects.all()[0]
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>>> c.point_of_contact = Employee.objects.create(firstname="Guido", lastname="van Rossum")
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>>> c.save()
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# F Expressions can also span joins
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>>> Company.objects.filter(ceo__firstname=F('point_of_contact__firstname')).distinct()
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[<Company: Foobar Ltd.>, <Company: Test GmbH>]
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>>> _ = Company.objects.exclude(ceo__firstname=F('point_of_contact__firstname')).update(name='foo')
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>>> Company.objects.exclude(ceo__firstname=F('point_of_contact__firstname')).get().name
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u'foo'
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>>> _ = Company.objects.exclude(ceo__firstname=F('point_of_contact__firstname')).update(name=F('point_of_contact__lastname'))
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Traceback (most recent call last):
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...
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FieldError: Joined field references are not permitted in this query
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# F expressions can be used to update attributes on single objects
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>>> test_gmbh = Company.objects.get(name='Test GmbH')
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>>> test_gmbh.num_employees
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32
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>>> test_gmbh.num_employees = F('num_employees') + 4
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>>> test_gmbh.save()
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>>> test_gmbh = Company.objects.get(pk=test_gmbh.pk)
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>>> test_gmbh.num_employees
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36
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# F expressions cannot be used to update attributes which are foreign keys, or
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# attributes which involve joins.
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>>> test_gmbh.point_of_contact = None
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>>> test_gmbh.save()
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>>> test_gmbh.point_of_contact is None
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True
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>>> test_gmbh.point_of_contact = F('ceo')
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Traceback (most recent call last):
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...
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ValueError: Cannot assign "<django.db.models.expressions.F object at ...>": "Company.point_of_contact" must be a "Employee" instance.
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>>> test_gmbh.point_of_contact = test_gmbh.ceo
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>>> test_gmbh.save()
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>>> test_gmbh.name = F('ceo__last_name')
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>>> test_gmbh.save()
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Traceback (most recent call last):
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...
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FieldError: Joined field references are not permitted in this query
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# F expressions cannot be used to update attributes on objects which do not yet
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# exist in the database
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>>> acme = Company(name='The Acme Widget Co.', num_employees=12, num_chairs=5,
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... ceo=test_gmbh.ceo)
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>>> acme.num_employees = F('num_employees') + 16
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>>> acme.save()
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Traceback (most recent call last):
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...
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TypeError: int() argument must be a string or a number...
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"""}
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