Changes between Initial Version and Version 1 of CookBookGenericAttribute

Timestamp:

Dec 13, 2006, 2:38:39 PM (19 years ago)

Author:

David S. <davidschein@…>

Comment:

--

CookBookGenericAttribute

@@ +1 @@
+See http://www.djangoproject.com/documentation/models/generic_relations/.
+
+'''Note''': As of today, 13-DEC-06, this admonishment applies: 
+{{{
+Generic relations: a "generic foreign key" feature is currently under development, 
+but not yet completed. There is no support for it yet in the admin application, and 
+it is probably unwise to attempt to use it in a production application.
+}}}
+--from http://code.djangoproject.com/ 
+
+Also, I do not think that this is particularly good data modeling if you have a choice, but when migrating an application and dealing with legacy data as you go, it can be useful if it is not abused.
+
+== Model Source Code ==
+{{{
+#!python
+class AttributeManager(models.Manager):
+    def with_attr(self, attr_name):
+        return Attribute.objects.filter(name=attr_name)
+
+    def type_with_attr(self, type_name, attr_name):
+        return Attribute.objects.filter(content_type__name=type_name, name=attr_name)
+
+    def type_with_attr_value(self, type_name, attr_name, value):
+        return Attribute.objects.filter(content_type__name=type_name, name=attr_name, value=value)
+
+    def obj_attr_list(self, obj):
+        ctype = ContentType.objects.get_for_model(obj)
+        return  Attribute.objects.filter(content_type__pk=ctype.id, object_id=obj.id)
+
+    def obj_attr_value(self, obj, attr_name):
+        ctype = ContentType.objects.get_for_model(obj)
+        try:
+            av = Attribute.objects.get(name=attr_name, content_type__pk=ctype.id, object_id=obj.id)
+        except Attribute.DoesNotExist:
+            return None
+        return av.value
+
+class Attribute(models.Model):
+    name = models.CharField(maxlength=25)
+    content_type = models.ForeignKey(ContentType)
+    object_id = models.PositiveIntegerField()
+    value = models.CharField(maxlength=255)
+   
+    content_object = models.GenericForeignKey()
+    objects = AttributeManager()
+
+    class meta:
+        unique_together = (('name', 'content_type', 'object_id'),)
+    
+    def __str__(self):
+        return "%s.%s.%s=%s" % (self.content_type.name, self.content_object, self.name, self.value,)
+}}}
+
+== Sample API usage ==
+This sample code assumes you added the above models to the sample found at http://www.djangoproject.com/documentation/models/generic_relations/.
+
+{{{
+#!python
+>>> diamond = Mineral.objects.create(name="Diamond", hardness=10)
+>>> emerald = Mineral.objects.create(name="Emerald", hardness=6)
+>>> Attribute.objects.create(content_object=quartz, name='color', value='black')
+<Attribute: mineral.Quartz.color=black>
+
+>>> Attribute.objects.create(content_object=emerald, name='color', value='green')
+<Attribute: mineral.Emerald.color=green>
+
+>>> Attribute.objects.with_attr('color')
+[<Attribute: mineral.Quartz.color=black>, <Attribute: mineral.Emerald.color=green>]
+
+>>> Attribute.objects.type_with_attr('mineral', 'color')
+[<Attribute: mineral.Quartz.color=black>, <Attribute: mineral.Emerald.color=green>]
+
+>>> Attribute.objects.create(content_object=eggplant, name='color', value='purple')
+<Attribute: vegetable.Eggplant.color=purple>
+
+>>> Attribute.objects.with_attr('color')
+[<Attribute: mineral.Quartz.color=black>, <Attribute: mineral.Emerald.color=green>, <Attribute: vegetable.Eggplant.color=
+purple>]
+
+>>> Attribute.objects.type_with_attr('mineral', 'color')
+[<Attribute: mineral.Quartz.color=black>, <Attribute: mineral.Emerald.color=green>]
+
+>>> Attribute.objects.type_with_attr_value('mineral', 'color', 'green')
+[<Attribute: mineral.Emerald.color=green>]
+
+>>> Attribute.objects.type_with_attr_value('mineral', 'color', 'red')
+[]
+
+>>> Attribute.objects.obj_attr_list(quartz)
+[<Attribute: mineral.Quartz.color=black>]
+
+>>> Attribute.objects.obj_attr_value(quartz, 'color')
+'black'
+}}}