~ubuntu-branches/ubuntu/quantal/python-django/quantal

"""

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.db import models

from django.contrib.contenttypes.models import ContentType

from django.contrib.contenttypes import generic

 

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", "-object_id"]

 

    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

 

__test__ = {'API_TESTS':"""

# Create the world in 7 lines of code...

>>> lion = Animal(common_name="Lion", latin_name="Panthera leo")

>>> platypus = Animal(common_name="Platypus", latin_name="Ornithorhynchus anatinus")

>>> eggplant = Vegetable(name="Eggplant", is_yucky=True)

>>> bacon = Vegetable(name="Bacon", is_yucky=False)

>>> quartz = Mineral(name="Quartz", hardness=7)

>>> for o in (platypus, lion, eggplant, bacon, quartz):

...     o.save()

 

# Objects with declared GenericRelations can be tagged directly -- the API

# mimics the many-to-many API.

>>> bacon.tags.create(tag="fatty")

<TaggedItem: fatty>

>>> bacon.tags.create(tag="salty")

<TaggedItem: salty>

>>> lion.tags.create(tag="yellow")

<TaggedItem: yellow>

>>> lion.tags.create(tag="hairy")

<TaggedItem: hairy>

>>> platypus.tags.create(tag="fatty")

<TaggedItem: fatty>

 

>>> lion.tags.all()

[<TaggedItem: hairy>, <TaggedItem: yellow>]

>>> bacon.tags.all()

[<TaggedItem: fatty>, <TaggedItem: salty>]

 

# You can easily access the content object like a foreign key.

>>> t = TaggedItem.objects.get(tag="salty")

>>> t.content_object

<Vegetable: Bacon>

 

# Recall that the Mineral class doesn't have an explicit GenericRelation

# defined. That's OK, because you can create TaggedItems explicitly.

>>> tag1 = TaggedItem(content_object=quartz, tag="shiny")

>>> tag2 = TaggedItem(content_object=quartz, tag="clearish")

>>> tag1.save()

>>> tag2.save()

 

# However, excluding GenericRelations means your lookups have to be a bit more

# explicit.

>>> from django.contrib.contenttypes.models import ContentType

>>> ctype = ContentType.objects.get_for_model(quartz)

>>> TaggedItem.objects.filter(content_type__pk=ctype.id, object_id=quartz.id)

[<TaggedItem: clearish>, <TaggedItem: shiny>]

 

# You can set a generic foreign key in the way you'd expect.

>>> tag1.content_object = platypus

>>> tag1.save()

>>> platypus.tags.all()

[<TaggedItem: fatty>, <TaggedItem: shiny>]

>>> TaggedItem.objects.filter(content_type__pk=ctype.id, object_id=quartz.id)

[<TaggedItem: clearish>]

 

# Queries across generic relations respect the content types. Even though there are two TaggedItems with a tag of "fatty", this query only pulls out the one with the content type related to Animals.

>>> Animal.objects.order_by('common_name')

[<Animal: Lion>, <Animal: Platypus>]

>>> Animal.objects.filter(tags__tag='fatty')

[<Animal: Platypus>]

>>> Animal.objects.exclude(tags__tag='fatty')

[<Animal: Lion>]

 

# If you delete an object with an explicit Generic relation, the related

# objects are deleted when the source object is deleted.

# Original list of tags:

>>> [(t.tag, t.content_type, t.object_id) for t in TaggedItem.objects.all()]

[(u'clearish', <ContentType: mineral>, 1), (u'fatty', <ContentType: vegetable>, 2), (u'fatty', <ContentType: animal>, 1), (u'hairy', <ContentType: animal>, 2), (u'salty', <ContentType: vegetable>, 2), (u'shiny', <ContentType: animal>, 1), (u'yellow', <ContentType: animal>, 2)]

 

>>> lion.delete()

>>> [(t.tag, t.content_type, t.object_id) for t in TaggedItem.objects.all()]

[(u'clearish', <ContentType: mineral>, 1), (u'fatty', <ContentType: vegetable>, 2), (u'fatty', <ContentType: animal>, 1), (u'salty', <ContentType: vegetable>, 2), (u'shiny', <ContentType: animal>, 1)]

 

# If Generic Relation is not explicitly defined, any related objects

# remain after deletion of the source object.

>>> quartz.delete()

>>> [(t.tag, t.content_type, t.object_id) for t in TaggedItem.objects.all()]

[(u'clearish', <ContentType: mineral>, 1), (u'fatty', <ContentType: vegetable>, 2), (u'fatty', <ContentType: animal>, 1), (u'salty', <ContentType: vegetable>, 2), (u'shiny', <ContentType: animal>, 1)]

 

# If you delete a tag, the objects using the tag are unaffected

# (other than losing a tag)

>>> tag = TaggedItem.objects.get(id=1)

>>> tag.delete()

>>> bacon.tags.all()

[<TaggedItem: salty>]

>>> [(t.tag, t.content_type, t.object_id) for t in TaggedItem.objects.all()]

[(u'clearish', <ContentType: mineral>, 1), (u'fatty', <ContentType: animal>, 1), (u'salty', <ContentType: vegetable>, 2), (u'shiny', <ContentType: animal>, 1)]

 

>>> TaggedItem.objects.filter(tag='fatty').delete()

 

>>> ctype = ContentType.objects.get_for_model(lion)

>>> Animal.objects.filter(tags__content_type=ctype)

[<Animal: Platypus>]

 

# Simple tests for multiple GenericForeignKeys

# only uses one model, since the above tests should be sufficient.

>>> tiger, cheetah, bear = Animal(common_name="tiger"), Animal(common_name="cheetah"), Animal(common_name="bear")

>>> for o in [tiger, cheetah, bear]: o.save()

 

# Create directly

>>> Comparison(first_obj=cheetah, other_obj=tiger, comparative="faster").save()

>>> Comparison(first_obj=tiger, other_obj=cheetah, comparative="cooler").save()

 

# Create using GenericRelation

>>> tiger.comparisons.create(other_obj=bear, comparative="cooler")

<Comparison: tiger is cooler than bear>

>>> tiger.comparisons.create(other_obj=cheetah, comparative="stronger")

<Comparison: tiger is stronger than cheetah>

 

>>> cheetah.comparisons.all()

[<Comparison: cheetah is faster than tiger>]

 

# Filtering works

>>> tiger.comparisons.filter(comparative="cooler")

[<Comparison: tiger is cooler than cheetah>, <Comparison: tiger is cooler than bear>]

 

# Filtering and deleting works

>>> subjective = ["cooler"]

>>> tiger.comparisons.filter(comparative__in=subjective).delete()

>>> Comparison.objects.all()

[<Comparison: cheetah is faster than tiger>, <Comparison: tiger is stronger than cheetah>]

 

# If we delete cheetah, Comparisons with cheetah as 'first_obj' will be deleted

# since Animal has an explicit GenericRelation to Comparison through first_obj.

# Comparisons with cheetah as 'other_obj' will not be deleted.

>>> cheetah.delete()

>>> Comparison.objects.all()

[<Comparison: tiger is stronger than None>]

 

# GenericForeignKey should work with subclasses (see #8309)

>>> quartz = Mineral.objects.create(name="Quartz", hardness=7)

>>> valuedtag = ValuableTaggedItem(content_object=quartz, tag="shiny", value=10)

>>> valuedtag.save()

>>> valuedtag.content_object

<Mineral: Quartz>

 

# GenericInlineFormSet tests ##################################################

 

>>> from django.contrib.contenttypes.generic import generic_inlineformset_factory

 

>>> GenericFormSet = generic_inlineformset_factory(TaggedItem, extra=1)

>>> formset = GenericFormSet()

>>> for form in formset.forms:

...     print form.as_p()

<p><label for="id_generic_relations-taggeditem-content_type-object_id-0-tag">Tag:</label> <input id="id_generic_relations-taggeditem-content_type-object_id-0-tag" type="text" name="generic_relations-taggeditem-content_type-object_id-0-tag" maxlength="50" /></p> 

<p><label for="id_generic_relations-taggeditem-content_type-object_id-0-DELETE">Delete:</label> <input type="checkbox" name="generic_relations-taggeditem-content_type-object_id-0-DELETE" id="id_generic_relations-taggeditem-content_type-object_id-0-DELETE" /><input type="hidden" name="generic_relations-taggeditem-content_type-object_id-0-id" id="id_generic_relations-taggeditem-content_type-object_id-0-id" /></p>

>>> formset = GenericFormSet(instance=Animal())

>>> for form in formset.forms:

...     print form.as_p()

<p><label for="id_generic_relations-taggeditem-content_type-object_id-0-tag">Tag:</label> <input id="id_generic_relations-taggeditem-content_type-object_id-0-tag" type="text" name="generic_relations-taggeditem-content_type-object_id-0-tag" maxlength="50" /></p>

<p><label for="id_generic_relations-taggeditem-content_type-object_id-0-DELETE">Delete:</label> <input type="checkbox" name="generic_relations-taggeditem-content_type-object_id-0-DELETE" id="id_generic_relations-taggeditem-content_type-object_id-0-DELETE" /><input type="hidden" name="generic_relations-taggeditem-content_type-object_id-0-id" id="id_generic_relations-taggeditem-content_type-object_id-0-id" /></p>

 

>>> formset = GenericFormSet(instance=platypus)

>>> for form in formset.forms:

...     print form.as_p()

<p><label for="id_generic_relations-taggeditem-content_type-object_id-0-tag">Tag:</label> <input id="id_generic_relations-taggeditem-content_type-object_id-0-tag" type="text" name="generic_relations-taggeditem-content_type-object_id-0-tag" value="shiny" maxlength="50" /></p>

<p><label for="id_generic_relations-taggeditem-content_type-object_id-0-DELETE">Delete:</label> <input type="checkbox" name="generic_relations-taggeditem-content_type-object_id-0-DELETE" id="id_generic_relations-taggeditem-content_type-object_id-0-DELETE" /><input type="hidden" name="generic_relations-taggeditem-content_type-object_id-0-id" value="..." id="id_generic_relations-taggeditem-content_type-object_id-0-id" /></p>

<p><label for="id_generic_relations-taggeditem-content_type-object_id-1-tag">Tag:</label> <input id="id_generic_relations-taggeditem-content_type-object_id-1-tag" type="text" name="generic_relations-taggeditem-content_type-object_id-1-tag" maxlength="50" /></p>

<p><label for="id_generic_relations-taggeditem-content_type-object_id-1-DELETE">Delete:</label> <input type="checkbox" name="generic_relations-taggeditem-content_type-object_id-1-DELETE" id="id_generic_relations-taggeditem-content_type-object_id-1-DELETE" /><input type="hidden" name="generic_relations-taggeditem-content_type-object_id-1-id" id="id_generic_relations-taggeditem-content_type-object_id-1-id" /></p>

 

>>> formset = GenericFormSet(instance=lion, prefix='x')

>>> for form in formset.forms:

...     print form.as_p()

<p><label for="id_x-0-tag">Tag:</label> <input id="id_x-0-tag" type="text" name="x-0-tag" maxlength="50" /></p>

<p><label for="id_x-0-DELETE">Delete:</label> <input type="checkbox" name="x-0-DELETE" id="id_x-0-DELETE" /><input type="hidden" name="x-0-id" id="id_x-0-id" /></p>

"""}