233 lines
6.9 KiB
Python
233 lines
6.9 KiB
Python
"""
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4. Many-to-one relationships
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To define a many-to-one relationship, use ``ForeignKey()`` .
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"""
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from django.db import models
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class Reporter(models.Model):
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first_name = models.CharField(maxlength=30)
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last_name = models.CharField(maxlength=30)
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email = models.EmailField()
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def __repr__(self):
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return "%s %s" % (self.first_name, self.last_name)
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class Article(models.Model):
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headline = models.CharField(maxlength=100)
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pub_date = models.DateField()
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reporter = models.ForeignKey(Reporter)
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def __repr__(self):
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return self.headline
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class Meta:
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ordering = ('headline',)
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API_TESTS = """
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# Create a few Reporters.
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>>> r = Reporter(first_name='John', last_name='Smith', email='john@example.com')
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>>> r.save()
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>>> r2 = Reporter(first_name='Paul', last_name='Jones', email='paul@example.com')
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>>> r2.save()
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# Create an Article.
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>>> from datetime import datetime
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>>> a = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter=r)
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>>> a.save()
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>>> a.reporter.id
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1
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>>> a.reporter
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John Smith
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# Article objects have access to their related Reporter objects.
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>>> r = a.reporter
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>>> r.first_name, r.last_name
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('John', 'Smith')
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# Create an Article via the Reporter object.
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>>> new_article = r.article_set.create(headline="John's second story", pub_date=datetime(2005, 7, 29))
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>>> new_article
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John's second story
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>>> new_article.reporter.id
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1
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# Create a new article, and add it to the article set.
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>>> new_article2 = Article(headline="Paul's story", pub_date=datetime(2006, 1, 17))
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>>> r.article_set.add(new_article2)
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>>> new_article2.reporter.id
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1
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>>> r.article_set.all()
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[John's second story, Paul's story, This is a test]
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# Add the same article to a different article set - check that it moves.
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>>> r2.article_set.add(new_article2)
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>>> new_article2.reporter.id
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2
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>>> r.article_set.all()
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[John's second story, This is a test]
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>>> r2.article_set.all()
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[Paul's story]
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# Assign the article to the reporter directly using the descriptor
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>>> new_article2.reporter = r
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>>> new_article2.save()
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>>> new_article2.reporter
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John Smith
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>>> new_article2.reporter.id
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1
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>>> r.article_set.all()
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[John's second story, Paul's story, This is a test]
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>>> r2.article_set.all()
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[]
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# Set the article back again using set descriptor.
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>>> r2.article_set = [new_article, new_article2]
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>>> r.article_set.all()
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[This is a test]
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>>> r2.article_set.all()
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[John's second story, Paul's story]
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# Funny case - assignment notation can only go so far; because the
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# ForeignKey cannot be null, existing members of the set must remain
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>>> r.article_set = [new_article]
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>>> r.article_set.all()
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[John's second story, This is a test]
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>>> r2.article_set.all()
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[Paul's story]
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# Reporter cannot be null - there should not be a clear or remove method
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>>> hasattr(r2.article_set, 'remove')
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False
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>>> hasattr(r2.article_set, 'clear')
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False
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# Reporter objects have access to their related Article objects.
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>>> r.article_set.all()
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[John's second story, This is a test]
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>>> r.article_set.filter(headline__startswith='This')
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[This is a test]
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>>> r.article_set.count()
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2
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>>> r2.article_set.count()
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1
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# Get articles by id
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>>> Article.objects.filter(id__exact=1)
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[This is a test]
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>>> Article.objects.filter(pk=1)
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[This is a test]
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# Query on an article property
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>>> Article.objects.filter(headline__startswith='This')
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[This is a test]
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# The API automatically follows relationships as far as you need.
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# Use double underscores to separate relationships.
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# This works as many levels deep as you want. There's no limit.
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# Find all Articles for any Reporter whose first name is "John".
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>>> Article.objects.filter(reporter__first_name__exact='John')
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[John's second story, This is a test]
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# Query twice over the related field.
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>>> Article.objects.filter(reporter__first_name__exact='John', reporter__last_name__exact='Smith')
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[John's second story, This is a test]
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# The underlying query only makes one join when a related table is referenced twice.
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>>> query = Article.objects.filter(reporter__first_name__exact='John', reporter__last_name__exact='Smith')
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>>> null, sql, null = query._get_sql_clause()
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>>> sql.count('INNER JOIN')
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1
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# The automatically joined table has a predictable name.
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>>> Article.objects.filter(reporter__first_name__exact='John').extra(where=["many_to_one_article__reporter.last_name='Smith'"])
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[John's second story, This is a test]
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# Find all Articles for the Reporter whose ID is 1.
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>>> Article.objects.filter(reporter__id__exact=1)
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[John's second story, This is a test]
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>>> Article.objects.filter(reporter__pk=1)
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[John's second story, This is a test]
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# You need two underscores between "reporter" and "id" -- not one.
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>>> Article.objects.filter(reporter_id__exact=1)
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Traceback (most recent call last):
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...
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TypeError: Cannot resolve keyword 'reporter_id' into field
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# You need to specify a comparison clause
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>>> Article.objects.filter(reporter_id=1)
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Traceback (most recent call last):
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...
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TypeError: Cannot resolve keyword 'reporter_id' into field
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# "pk" shortcut syntax works in a related context, too.
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>>> Article.objects.filter(reporter__pk=1)
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[John's second story, This is a test]
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# You can also instantiate an Article by passing
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# the Reporter's ID instead of a Reporter object.
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>>> a3 = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter_id=r.id)
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>>> a3.save()
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>>> a3.reporter.id
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1
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>>> a3.reporter
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John Smith
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# Similarly, the reporter ID can be a string.
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>>> a4 = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter_id="1")
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>>> a4.save()
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>>> a4.reporter
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John Smith
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# Reporters can be queried
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>>> Reporter.objects.filter(id__exact=1)
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[John Smith]
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>>> Reporter.objects.filter(pk=1)
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[John Smith]
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>>> Reporter.objects.filter(first_name__startswith='John')
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[John Smith]
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# Reporters can query in opposite direction of ForeignKey definition
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>>> Reporter.objects.filter(article__id__exact=1)
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[John Smith]
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>>> Reporter.objects.filter(article__pk=1)
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[John Smith]
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>>> Reporter.objects.filter(article__headline__startswith='This')
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[John Smith, John Smith, John Smith]
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>>> Reporter.objects.filter(article__headline__startswith='This').distinct()
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[John Smith]
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# Queries can go round in circles.
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>>> Reporter.objects.filter(article__reporter__first_name__startswith='John')
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[John Smith, John Smith, John Smith, John Smith]
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>>> Reporter.objects.filter(article__reporter__first_name__startswith='John').distinct()
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[John Smith]
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# If you delete a reporter, his articles will be deleted.
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>>> Article.objects.all()
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[John's second story, Paul's story, This is a test, This is a test, This is a test]
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>>> Reporter.objects.order_by('first_name')
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[John Smith, Paul Jones]
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>>> r2.delete()
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>>> Article.objects.all()
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[John's second story, This is a test, This is a test, This is a test]
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>>> Reporter.objects.order_by('first_name')
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[John Smith]
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# Deletes using a join in the query
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>>> Reporter.objects.filter(article__headline__startswith='This').delete()
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>>> Reporter.objects.all()
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[]
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>>> Article.objects.all()
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[]
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"""
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