1 """

     2 20. Multiple many-to-many relationships between the same two tables

     3 

     4 In this example, an Article can have many Categories (as "primary") and many

     5 Categories (as "secondary").

     6 

     7 Set ``related_name`` to designate what the reverse relationship is called.

     8 """

     9 

    10 from django.db import models

    11 

    12 class Category(models.Model):

    13     name = models.CharField(maxlength=20)

    14     class Meta:

    15        ordering = ('name',)

    16 

    17     def __str__(self):

    18         return self.name

    19 

    20 class Article(models.Model):

    21     headline = models.CharField(maxlength=50)

    22     pub_date = models.DateTimeField()

    23     primary_categories = models.ManyToManyField(Category, related_name='primary_article_set')

    24     secondary_categories = models.ManyToManyField(Category, related_name='secondary_article_set')

    25     class Meta:

    26        ordering = ('pub_date',)

    27 

    28     def __str__(self):

    29         return self.headline

    30 

    31 __test__ = {'API_TESTS':"""

    32 >>> from datetime import datetime

    33 

    34 >>> c1 = Category(name='Sports')

    35 >>> c1.save()

    36 >>> c2 = Category(name='News')

    37 >>> c2.save()

    38 >>> c3 = Category(name='Crime')

    39 >>> c3.save()

    40 >>> c4 = Category(name='Life')

    41 >>> c4.save()

    42 

    43 >>> a1 = Article(headline='Area man steals', pub_date=datetime(2005, 11, 27))

    44 >>> a1.save()

    45 >>> a1.primary_categories.add(c2, c3)

    46 >>> a1.secondary_categories.add(c4)

    47 

    48 >>> a2 = Article(headline='Area man runs', pub_date=datetime(2005, 11, 28))

    49 >>> a2.save()

    50 >>> a2.primary_categories.add(c1, c2)

    51 >>> a2.secondary_categories.add(c4)

    52 

    53 >>> a1.primary_categories.all()

    54 [<Category: Crime>, <Category: News>]

    55 

    56 >>> a2.primary_categories.all()

    57 [<Category: News>, <Category: Sports>]

    58 

    59 >>> a1.secondary_categories.all()

    60 [<Category: Life>]

    61 

    62 

    63 >>> c1.primary_article_set.all()

    64 [<Article: Area man runs>]

    65 >>> c1.secondary_article_set.all()

    66 []

    67 >>> c2.primary_article_set.all()

    68 [<Article: Area man steals>, <Article: Area man runs>]

    69 >>> c2.secondary_article_set.all()

    70 []

    71 >>> c3.primary_article_set.all()

    72 [<Article: Area man steals>]

    73 >>> c3.secondary_article_set.all()

    74 []

    75 >>> c4.primary_article_set.all()

    76 []

    77 >>> c4.secondary_article_set.all()

    78 [<Article: Area man steals>, <Article: Area man runs>]

    79 """}