352 lines
13 KiB
Python
352 lines
13 KiB
Python
"""
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7. The lookup API
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This demonstrates features of the database API.
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"""
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from django.db import models
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from django.conf import settings
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class Article(models.Model):
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headline = models.CharField(maxlength=100)
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pub_date = models.DateTimeField()
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class Meta:
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ordering = ('-pub_date', 'headline')
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def __unicode__(self):
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return self.headline
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__test__ = {'API_TESTS':r"""
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# Create a couple of Articles.
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>>> from datetime import datetime
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>>> a1 = Article(headline='Article 1', pub_date=datetime(2005, 7, 26))
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>>> a1.save()
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>>> a2 = Article(headline='Article 2', pub_date=datetime(2005, 7, 27))
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>>> a2.save()
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>>> a3 = Article(headline='Article 3', pub_date=datetime(2005, 7, 27))
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>>> a3.save()
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>>> a4 = Article(headline='Article 4', pub_date=datetime(2005, 7, 28))
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>>> a4.save()
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>>> a5 = Article(headline='Article 5', pub_date=datetime(2005, 8, 1, 9, 0))
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>>> a5.save()
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>>> a6 = Article(headline='Article 6', pub_date=datetime(2005, 8, 1, 8, 0))
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>>> a6.save()
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>>> a7 = Article(headline='Article 7', pub_date=datetime(2005, 7, 27))
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>>> a7.save()
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# Each QuerySet gets iterator(), which is a generator that "lazily" returns
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# results using database-level iteration.
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>>> for a in Article.objects.iterator():
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... print a.headline
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Article 5
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Article 6
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Article 4
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Article 2
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Article 3
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Article 7
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Article 1
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# iterator() can be used on any QuerySet.
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>>> for a in Article.objects.filter(headline__endswith='4').iterator():
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... print a.headline
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Article 4
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# count() returns the number of objects matching search criteria.
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>>> Article.objects.count()
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7L
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>>> Article.objects.filter(pub_date__exact=datetime(2005, 7, 27)).count()
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3L
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>>> Article.objects.filter(headline__startswith='Blah blah').count()
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0L
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# count() should respect sliced query sets.
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>>> articles = Article.objects.all()
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>>> articles.count()
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7L
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>>> articles[:4].count()
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4
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>>> articles[1:100].count()
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6L
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>>> articles[10:100].count()
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0
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# Date and date/time lookups can also be done with strings.
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>>> Article.objects.filter(pub_date__exact='2005-07-27 00:00:00').count()
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3L
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# in_bulk() takes a list of IDs and returns a dictionary mapping IDs
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# to objects.
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>>> Article.objects.in_bulk([1, 2])
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{1: <Article: Article 1>, 2: <Article: Article 2>}
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>>> Article.objects.in_bulk([3])
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{3: <Article: Article 3>}
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>>> Article.objects.in_bulk([1000])
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{}
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>>> Article.objects.in_bulk([])
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{}
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>>> Article.objects.in_bulk('foo')
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Traceback (most recent call last):
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...
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AssertionError: in_bulk() must be provided with a list of IDs.
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>>> Article.objects.in_bulk()
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Traceback (most recent call last):
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...
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TypeError: in_bulk() takes exactly 2 arguments (1 given)
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>>> Article.objects.in_bulk(headline__startswith='Blah')
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Traceback (most recent call last):
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...
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TypeError: in_bulk() got an unexpected keyword argument 'headline__startswith'
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# values() returns a list of dictionaries instead of object instances -- and
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# you can specify which fields you want to retrieve.
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>>> Article.objects.values('headline')
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[{'headline': u'Article 5'}, {'headline': u'Article 6'}, {'headline': u'Article 4'}, {'headline': u'Article 2'}, {'headline': u'Article 3'}, {'headline': u'Article 7'}, {'headline': u'Article 1'}]
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>>> Article.objects.filter(pub_date__exact=datetime(2005, 7, 27)).values('id')
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[{'id': 2}, {'id': 3}, {'id': 7}]
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>>> list(Article.objects.values('id', 'headline')) == [{'id': 5, 'headline': 'Article 5'}, {'id': 6, 'headline': 'Article 6'}, {'id': 4, 'headline': 'Article 4'}, {'id': 2, 'headline': 'Article 2'}, {'id': 3, 'headline': 'Article 3'}, {'id': 7, 'headline': 'Article 7'}, {'id': 1, 'headline': 'Article 1'}]
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True
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>>> for d in Article.objects.values('id', 'headline'):
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... i = d.items()
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... i.sort()
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... i
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[('headline', u'Article 5'), ('id', 5)]
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[('headline', u'Article 6'), ('id', 6)]
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[('headline', u'Article 4'), ('id', 4)]
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[('headline', u'Article 2'), ('id', 2)]
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[('headline', u'Article 3'), ('id', 3)]
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[('headline', u'Article 7'), ('id', 7)]
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[('headline', u'Article 1'), ('id', 1)]
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# You can use values() with iterator() for memory savings, because iterator()
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# uses database-level iteration.
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>>> for d in Article.objects.values('id', 'headline').iterator():
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... i = d.items()
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... i.sort()
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... i
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[('headline', u'Article 5'), ('id', 5)]
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[('headline', u'Article 6'), ('id', 6)]
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[('headline', u'Article 4'), ('id', 4)]
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[('headline', u'Article 2'), ('id', 2)]
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[('headline', u'Article 3'), ('id', 3)]
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[('headline', u'Article 7'), ('id', 7)]
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[('headline', u'Article 1'), ('id', 1)]
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# you can use values() even on extra fields
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>>> for d in Article.objects.extra( select={'id_plus_one' : 'id + 1'} ).values('id', 'id_plus_one'):
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... i = d.items()
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... i.sort()
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... i
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[('id', 5), ('id_plus_one', 6)]
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[('id', 6), ('id_plus_one', 7)]
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[('id', 4), ('id_plus_one', 5)]
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[('id', 2), ('id_plus_one', 3)]
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[('id', 3), ('id_plus_one', 4)]
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[('id', 7), ('id_plus_one', 8)]
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[('id', 1), ('id_plus_one', 2)]
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# however, an exception FieldDoesNotExist will still be thrown
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# if you try to access non-existent field (field that is neither on the model nor extra)
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>>> Article.objects.extra( select={'id_plus_one' : 'id + 1'} ).values('id', 'id_plus_two')
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Traceback (most recent call last):
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...
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FieldDoesNotExist: Article has no field named 'id_plus_two'
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# if you don't specify which fields, all are returned
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>>> list(Article.objects.filter(id=5).values()) == [{'id': 5, 'headline': 'Article 5', 'pub_date': datetime(2005, 8, 1, 9, 0)}]
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True
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# Every DateField and DateTimeField creates get_next_by_FOO() and
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# get_previous_by_FOO() methods.
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# In the case of identical date values, these methods will use the ID as a
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# fallback check. This guarantees that no records are skipped or duplicated.
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>>> a1.get_next_by_pub_date()
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<Article: Article 2>
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>>> a2.get_next_by_pub_date()
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<Article: Article 3>
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>>> a2.get_next_by_pub_date(headline__endswith='6')
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<Article: Article 6>
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>>> a3.get_next_by_pub_date()
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<Article: Article 7>
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>>> a4.get_next_by_pub_date()
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<Article: Article 6>
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>>> a5.get_next_by_pub_date()
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Traceback (most recent call last):
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...
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DoesNotExist: Article matching query does not exist.
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>>> a6.get_next_by_pub_date()
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<Article: Article 5>
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>>> a7.get_next_by_pub_date()
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<Article: Article 4>
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>>> a7.get_previous_by_pub_date()
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<Article: Article 3>
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>>> a6.get_previous_by_pub_date()
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<Article: Article 4>
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>>> a5.get_previous_by_pub_date()
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<Article: Article 6>
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>>> a4.get_previous_by_pub_date()
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<Article: Article 7>
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>>> a3.get_previous_by_pub_date()
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<Article: Article 2>
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>>> a2.get_previous_by_pub_date()
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<Article: Article 1>
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# Underscores and percent signs have special meaning in the underlying
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# SQL code, but Django handles the quoting of them automatically.
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>>> a8 = Article(headline='Article_ with underscore', pub_date=datetime(2005, 11, 20))
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>>> a8.save()
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>>> Article.objects.filter(headline__startswith='Article')
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[<Article: Article_ with underscore>, <Article: Article 5>, <Article: Article 6>, <Article: Article 4>, <Article: Article 2>, <Article: Article 3>, <Article: Article 7>, <Article: Article 1>]
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>>> Article.objects.filter(headline__startswith='Article_')
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[<Article: Article_ with underscore>]
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>>> a9 = Article(headline='Article% with percent sign', pub_date=datetime(2005, 11, 21))
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>>> a9.save()
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>>> Article.objects.filter(headline__startswith='Article')
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[<Article: Article% with percent sign>, <Article: Article_ with underscore>, <Article: Article 5>, <Article: Article 6>, <Article: Article 4>, <Article: Article 2>, <Article: Article 3>, <Article: Article 7>, <Article: Article 1>]
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>>> Article.objects.filter(headline__startswith='Article%')
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[<Article: Article% with percent sign>]
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# exclude() is the opposite of filter() when doing lookups:
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>>> Article.objects.filter(headline__contains='Article').exclude(headline__contains='with')
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[<Article: Article 5>, <Article: Article 6>, <Article: Article 4>, <Article: Article 2>, <Article: Article 3>, <Article: Article 7>, <Article: Article 1>]
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>>> Article.objects.exclude(headline__startswith="Article_")
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[<Article: Article% with percent sign>, <Article: Article 5>, <Article: Article 6>, <Article: Article 4>, <Article: Article 2>, <Article: Article 3>, <Article: Article 7>, <Article: Article 1>]
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>>> Article.objects.exclude(headline="Article 7")
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[<Article: Article% with percent sign>, <Article: Article_ with underscore>, <Article: Article 5>, <Article: Article 6>, <Article: Article 4>, <Article: Article 2>, <Article: Article 3>, <Article: Article 1>]
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# Backslashes also have special meaning in the underlying SQL code, but Django
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# automatically quotes them appropriately.
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>>> a10 = Article(headline='Article with \\ backslash', pub_date=datetime(2005, 11, 22))
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>>> a10.save()
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>>> Article.objects.filter(headline__contains='\\')
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[<Article: Article with \ backslash>]
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# none() returns an EmptyQuerySet that behaves like any other QuerySet object
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>>> Article.objects.none()
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[]
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>>> Article.objects.none().filter(headline__startswith='Article')
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[]
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>>> Article.objects.none().count()
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0
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>>> [article for article in Article.objects.none().iterator()]
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[]
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# using __in with an empty list should return an empty query set
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>>> Article.objects.filter(id__in=[])
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[]
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>>> Article.objects.exclude(id__in=[])
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[<Article: Article with \ backslash>, <Article: Article% with percent sign>, <Article: Article_ with underscore>, <Article: Article 5>, <Article: Article 6>, <Article: Article 4>, <Article: Article 2>, <Article: Article 3>, <Article: Article 7>, <Article: Article 1>]
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# Programming errors are pointed out with nice error messages
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>>> Article.objects.filter(pub_date_year='2005').count()
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Traceback (most recent call last):
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...
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TypeError: Cannot resolve keyword 'pub_date_year' into field. Choices are: id, headline, pub_date
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>>> Article.objects.filter(headline__starts='Article')
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Traceback (most recent call last):
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...
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TypeError: Cannot resolve keyword 'headline__starts' into field. Choices are: id, headline, pub_date
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# Create some articles with a bit more interesting headlines for testing field lookups:
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>>> now = datetime.now()
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>>> for a in Article.objects.all():
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... a.delete()
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>>> a1 = Article(pub_date=now, headline='f')
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>>> a1.save()
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>>> a2 = Article(pub_date=now, headline='fo')
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>>> a2.save()
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>>> a3 = Article(pub_date=now, headline='foo')
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>>> a3.save()
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>>> a4 = Article(pub_date=now, headline='fooo')
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>>> a4.save()
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>>> a5 = Article(pub_date=now, headline='hey-Foo')
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>>> a5.save()
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# zero-or-more
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>>> Article.objects.filter(headline__regex=r'fo*')
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[<Article: f>, <Article: fo>, <Article: foo>, <Article: fooo>]
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>>> Article.objects.filter(headline__iregex=r'fo*')
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[<Article: f>, <Article: fo>, <Article: foo>, <Article: fooo>, <Article: hey-Foo>]
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# one-or-more
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>>> Article.objects.filter(headline__regex=r'fo+')
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[<Article: fo>, <Article: foo>, <Article: fooo>]
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# wildcard
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>>> Article.objects.filter(headline__regex=r'fooo?')
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[<Article: foo>, <Article: fooo>]
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# and some more:
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>>> a6 = Article(pub_date=now, headline='bar')
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>>> a6.save()
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>>> a7 = Article(pub_date=now, headline='AbBa')
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>>> a7.save()
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>>> a8 = Article(pub_date=now, headline='baz')
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>>> a8.save()
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>>> a9 = Article(pub_date=now, headline='baxZ')
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>>> a9.save()
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# leading anchor
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>>> Article.objects.filter(headline__regex=r'^b')
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[<Article: bar>, <Article: baxZ>, <Article: baz>]
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>>> Article.objects.filter(headline__iregex=r'^a')
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[<Article: AbBa>]
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# trailing anchor
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>>> Article.objects.filter(headline__regex=r'z$')
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[<Article: baz>]
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>>> Article.objects.filter(headline__iregex=r'z$')
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[<Article: baxZ>, <Article: baz>]
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# character sets
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>>> Article.objects.filter(headline__regex=r'ba[rz]')
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[<Article: bar>, <Article: baz>]
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>>> Article.objects.filter(headline__regex=r'ba.[RxZ]')
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[<Article: baxZ>]
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>>> Article.objects.filter(headline__iregex=r'ba[RxZ]')
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[<Article: bar>, <Article: baxZ>, <Article: baz>]
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# and yet more:
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>>> a10 = Article(pub_date=now, headline='foobar')
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>>> a10.save()
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>>> a11 = Article(pub_date=now, headline='foobaz')
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>>> a11.save()
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>>> a12 = Article(pub_date=now, headline='ooF')
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>>> a12.save()
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>>> a13 = Article(pub_date=now, headline='foobarbaz')
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>>> a13.save()
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>>> a14 = Article(pub_date=now, headline='zoocarfaz')
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>>> a14.save()
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>>> a15 = Article(pub_date=now, headline='barfoobaz')
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>>> a15.save()
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>>> a16 = Article(pub_date=now, headline='bazbaRFOO')
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>>> a16.save()
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# alternation
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>>> Article.objects.filter(headline__regex=r'oo(f|b)')
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[<Article: barfoobaz>, <Article: foobar>, <Article: foobarbaz>, <Article: foobaz>]
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>>> Article.objects.filter(headline__iregex=r'oo(f|b)')
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[<Article: barfoobaz>, <Article: foobar>, <Article: foobarbaz>, <Article: foobaz>, <Article: ooF>]
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>>> Article.objects.filter(headline__regex=r'^foo(f|b)')
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[<Article: foobar>, <Article: foobarbaz>, <Article: foobaz>]
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# greedy matching
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>>> Article.objects.filter(headline__regex=r'b.*az')
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[<Article: barfoobaz>, <Article: baz>, <Article: bazbaRFOO>, <Article: foobarbaz>, <Article: foobaz>]
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>>> Article.objects.filter(headline__iregex=r'b.*ar')
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[<Article: bar>, <Article: barfoobaz>, <Article: bazbaRFOO>, <Article: foobar>, <Article: foobarbaz>]
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"""}
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if settings.DATABASE_ENGINE not in ('mysql', 'mysql_old'):
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__test__['API_TESTS'] += r"""
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# grouping and backreferences
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>>> Article.objects.filter(headline__regex=r'b(.).*b\1')
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[<Article: barfoobaz>, <Article: bazbaRFOO>, <Article: foobarbaz>]
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"""
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