180 lines
6.4 KiB
Python
180 lines
6.4 KiB
Python
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"""
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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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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 __repr__(self):
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return self.headline
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API_TESTS = """
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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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# 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 1, 2: Article 2}
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>>> Article.objects.in_bulk([3])
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{3: 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': 'Article 5'}, {'headline': 'Article 6'}, {'headline': 'Article 4'}, {'headline': 'Article 2'}, {'headline': 'Article 3'}, {'headline': 'Article 7'}, {'headline': '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', 'Article 5'), ('id', 5)]
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[('headline', 'Article 6'), ('id', 6)]
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[('headline', 'Article 4'), ('id', 4)]
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[('headline', 'Article 2'), ('id', 2)]
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[('headline', 'Article 3'), ('id', 3)]
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[('headline', 'Article 7'), ('id', 7)]
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[('headline', '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', 'Article 5'), ('id', 5)]
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[('headline', 'Article 6'), ('id', 6)]
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[('headline', 'Article 4'), ('id', 4)]
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[('headline', 'Article 2'), ('id', 2)]
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[('headline', 'Article 3'), ('id', 3)]
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[('headline', 'Article 7'), ('id', 7)]
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[('headline', 'Article 1'), ('id', 1)]
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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 2
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>>> a2.get_next_by_pub_date()
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Article 3
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>>> a3.get_next_by_pub_date()
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Article 7
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>>> a4.get_next_by_pub_date()
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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 does not exist for ...
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>>> a6.get_next_by_pub_date()
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Article 5
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>>> a7.get_next_by_pub_date()
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Article 4
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>>> a7.get_previous_by_pub_date()
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Article 3
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>>> a6.get_previous_by_pub_date()
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Article 4
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>>> a5.get_previous_by_pub_date()
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Article 6
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>>> a4.get_previous_by_pub_date()
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Article 7
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>>> a3.get_previous_by_pub_date()
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Article 2
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>>> a2.get_previous_by_pub_date()
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Article 1
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# Underscores and percent signs have special meaning in the underlying
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# database library, 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_ with underscore, Article 5, Article 6, Article 4, Article 2, Article 3, Article 7, Article 1]
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>>> Article.objects.filter(headline__startswith='Article_')
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[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% with percent sign, Article_ with underscore, Article 5, Article 6, Article 4, Article 2, Article 3, Article 7, Article 1]
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>>> Article.objects.filter(headline__startswith='Article%')
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[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 5, Article 6, Article 4, Article 2, Article 3, Article 7, Article 1]
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>>> Article.objects.exclude(headline__startswith="Article_")
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[Article% with percent sign, Article 5, Article 6, Article 4, Article 2, Article 3, Article 7, Article 1]
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>>> Article.objects.exclude(headline="Article 7")
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[Article% with percent sign, Article_ with underscore, Article 5, Article 6, Article 4, Article 2, Article 3, Article 1]
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"""
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