"""

34. Generic relations

Generic relations let an object have a foreign key to any object through a

content-type/object-id field. A ``GenericForeignKey`` field can point to any

object, be it animal, vegetable, or mineral.

The canonical example is tags (although this example implementation is *far*

from complete).

"""

from django.contrib.contenttypes import generic

from django.contrib.contenttypes.models import ContentType

from django.db import models

class TaggedItem(models.Model):

    """A tag on an item."""

    tag = models.SlugField()

    content_type = models.ForeignKey(ContentType)

    object_id = models.PositiveIntegerField()

    content_object = generic.GenericForeignKey()

    class Meta:

        ordering = ["tag", "content_type__name"]

    def __unicode__(self):

        return self.tag

class ValuableTaggedItem(TaggedItem):

    value = models.PositiveIntegerField()

class Comparison(models.Model):

    """

    A model that tests having multiple GenericForeignKeys

    """

    comparative = models.CharField(max_length=50)

    content_type1 = models.ForeignKey(ContentType, related_name="comparative1_set")

    object_id1 = models.PositiveIntegerField()

    content_type2 = models.ForeignKey(ContentType,  related_name="comparative2_set")

    object_id2 = models.PositiveIntegerField()

    first_obj = generic.GenericForeignKey(ct_field="content_type1", fk_field="object_id1")

    other_obj = generic.GenericForeignKey(ct_field="content_type2", fk_field="object_id2")

    def __unicode__(self):

        return u"%s is %s than %s" % (self.first_obj, self.comparative, self.other_obj)

class Animal(models.Model):

    common_name = models.CharField(max_length=150)

    latin_name = models.CharField(max_length=150)

    tags = generic.GenericRelation(TaggedItem)

    comparisons = generic.GenericRelation(Comparison,

                                          object_id_field="object_id1",

                                          content_type_field="content_type1")

    def __unicode__(self):

        return self.common_name

class Vegetable(models.Model):

    name = models.CharField(max_length=150)

    is_yucky = models.BooleanField(default=True)

    tags = generic.GenericRelation(TaggedItem)

    def __unicode__(self):

        return self.name

class Mineral(models.Model):

    name = models.CharField(max_length=150)

    hardness = models.PositiveSmallIntegerField()

    # note the lack of an explicit GenericRelation here...

    def __unicode__(self):

        return self.name