author | Sverre Rabbelier <srabbelier@gmail.com> |
Thu, 02 Apr 2009 23:05:31 +0000 | |
changeset 2056 | bbd16a156bde |
parent 109 | 620f9b141567 |
permissions | -rwxr-xr-x |
109
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Load ../../google_appengine into trunk/thirdparty/google_appengine.
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parents:
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""" |
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9. Many-to-many relationships via an intermediary table |
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|
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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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|
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from django.db import models |
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|
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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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|
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def __str__(self): |
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return "%s %s" % (self.first_name, self.last_name) |
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|
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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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__test__ = {'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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"""} |