81 lines
2.5 KiB
Python
81 lines
2.5 KiB
Python
"""
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34. Generic relations
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Generic relations let an object have a foreign key to any object through a
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content-type/object-id field. A ``GenericForeignKey`` field can point to any
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object, be it animal, vegetable, or mineral.
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The canonical example is tags (although this example implementation is *far*
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from complete).
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"""
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from django.contrib.contenttypes import generic
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from django.contrib.contenttypes.models import ContentType
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from django.db import models
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class TaggedItem(models.Model):
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"""A tag on an item."""
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tag = models.SlugField()
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content_type = models.ForeignKey(ContentType)
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object_id = models.PositiveIntegerField()
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content_object = generic.GenericForeignKey()
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class Meta:
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ordering = ["tag", "content_type__name"]
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def __unicode__(self):
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return self.tag
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class ValuableTaggedItem(TaggedItem):
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value = models.PositiveIntegerField()
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class Comparison(models.Model):
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"""
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A model that tests having multiple GenericForeignKeys
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"""
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comparative = models.CharField(max_length=50)
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content_type1 = models.ForeignKey(ContentType, related_name="comparative1_set")
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object_id1 = models.PositiveIntegerField()
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content_type2 = models.ForeignKey(ContentType, related_name="comparative2_set")
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object_id2 = models.PositiveIntegerField()
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first_obj = generic.GenericForeignKey(ct_field="content_type1", fk_field="object_id1")
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other_obj = generic.GenericForeignKey(ct_field="content_type2", fk_field="object_id2")
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def __unicode__(self):
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return u"%s is %s than %s" % (self.first_obj, self.comparative, self.other_obj)
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class Animal(models.Model):
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common_name = models.CharField(max_length=150)
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latin_name = models.CharField(max_length=150)
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tags = generic.GenericRelation(TaggedItem)
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comparisons = generic.GenericRelation(Comparison,
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object_id_field="object_id1",
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content_type_field="content_type1")
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def __unicode__(self):
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return self.common_name
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class Vegetable(models.Model):
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name = models.CharField(max_length=150)
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is_yucky = models.BooleanField(default=True)
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tags = generic.GenericRelation(TaggedItem)
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def __unicode__(self):
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return self.name
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class Mineral(models.Model):
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name = models.CharField(max_length=150)
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hardness = models.PositiveSmallIntegerField()
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# note the lack of an explicit GenericRelation here...
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def __unicode__(self):
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return self.name
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