1 """ |
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2 9. Many-to-many relationships via an intermediary table |
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3 |
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4 For many-to-many relationships that need extra fields on the intermediary |
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5 table, use an intermediary model. |
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6 |
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7 In this example, an ``Article`` can have multiple ``Reporter``s, and each |
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8 ``Article``-``Reporter`` combination (a ``Writer``) has a ``position`` field, |
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9 which specifies the ``Reporter``'s position for the given article (e.g. "Staff |
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10 writer"). |
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11 """ |
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12 |
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13 from django.db import models |
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14 |
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15 class Reporter(models.Model): |
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16 first_name = models.CharField(maxlength=30) |
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17 last_name = models.CharField(maxlength=30) |
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18 |
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19 def __str__(self): |
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20 return "%s %s" % (self.first_name, self.last_name) |
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21 |
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22 class Article(models.Model): |
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23 headline = models.CharField(maxlength=100) |
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24 pub_date = models.DateField() |
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25 |
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26 def __str__(self): |
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27 return self.headline |
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28 |
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29 class Writer(models.Model): |
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30 reporter = models.ForeignKey(Reporter) |
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31 article = models.ForeignKey(Article) |
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32 position = models.CharField(maxlength=100) |
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33 |
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34 def __str__(self): |
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35 return '%s (%s)' % (self.reporter, self.position) |
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36 |
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37 __test__ = {'API_TESTS':""" |
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38 # Create a few Reporters. |
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39 >>> r1 = Reporter(first_name='John', last_name='Smith') |
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40 >>> r1.save() |
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41 >>> r2 = Reporter(first_name='Jane', last_name='Doe') |
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42 >>> r2.save() |
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43 |
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44 # Create an Article. |
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45 >>> from datetime import datetime |
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46 >>> a = Article(headline='This is a test', pub_date=datetime(2005, 7, 27)) |
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47 >>> a.save() |
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48 |
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49 # Create a few Writers. |
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50 >>> w1 = Writer(reporter=r1, article=a, position='Main writer') |
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51 >>> w1.save() |
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52 >>> w2 = Writer(reporter=r2, article=a, position='Contributor') |
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53 >>> w2.save() |
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54 |
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55 # Play around with the API. |
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56 >>> a.writer_set.select_related().order_by('-position') |
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57 [<Writer: John Smith (Main writer)>, <Writer: Jane Doe (Contributor)>] |
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58 >>> w1.reporter |
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59 <Reporter: John Smith> |
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60 >>> w2.reporter |
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61 <Reporter: Jane Doe> |
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62 >>> w1.article |
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63 <Article: This is a test> |
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64 >>> w2.article |
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65 <Article: This is a test> |
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66 >>> r1.writer_set.all() |
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67 [<Writer: John Smith (Main writer)>] |
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68 """} |
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