69 lines
1.9 KiB
Python
69 lines
1.9 KiB
Python
"""
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9. Many-to-many relationships via an intermediary table
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For many-to-many relationships that need extra fields on the intermediary
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table, use an intermediary model.
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In this example, an ``Article`` can have multiple ``Reporter``s, and each
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``Article``-``Reporter`` combination (a ``Writer``) has a ``position`` field,
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which specifies the ``Reporter``'s position for the given article (e.g. "Staff
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writer").
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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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def __str__(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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def __str__(self):
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return self.headline
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class Writer(models.Model):
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reporter = models.ForeignKey(Reporter)
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article = models.ForeignKey(Article)
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position = models.CharField(maxlength=100)
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def __str__(self):
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return '%s (%s)' % (self.reporter, self.position)
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API_TESTS = """
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# Create a few Reporters.
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>>> r1 = Reporter(first_name='John', last_name='Smith')
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>>> r1.save()
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>>> r2 = Reporter(first_name='Jane', last_name='Doe')
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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(headline='This is a test', pub_date=datetime(2005, 7, 27))
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>>> a.save()
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# Create a few Writers.
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>>> w1 = Writer(reporter=r1, article=a, position='Main writer')
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>>> w1.save()
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>>> w2 = Writer(reporter=r2, article=a, position='Contributor')
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>>> w2.save()
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# Play around with the API.
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>>> a.writer_set.select_related().order_by('-position')
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[<Writer: John Smith (Main writer)>, <Writer: Jane Doe (Contributor)>]
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>>> w1.reporter
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<Reporter: John Smith>
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>>> w2.reporter
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<Reporter: Jane Doe>
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>>> w1.article
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<Article: This is a test>
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>>> w2.article
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<Article: This is a test>
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>>> r1.writer_set.all()
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[<Writer: John Smith (Main writer)>]
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"""
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