All,
I'm seeing some unexpected behavior when using multi-level multi-table
inheritance. In the example below there are three levels in the class
hierarchy. When accessing the name field (which is stored in the Level1 base
class) from an object in Level3, the query does not seem to walk the hierarchy
correctly.
Note: I am using explicitly defined id and OneToOneFields so that I can
specify the db_column names (for compatibility with other legacy software using
the same database). Here's the models file, followed by a console log where I
created test objects (in an otherwise blank database):
# models.py
from django.db import models
class Level1(models.Model):
""" Top level base class """
level1_id = models.AutoField(primary_key=True, db_column='Level1_ID')
name = models.CharField(max_length=32, db_column='Name', blank=True,
null=True)
class Meta:
db_table = 'Level1'
class Level2(Level1):
""" Middle level class """
level2_id = models.AutoField(primary_key=True, db_column='Level2_ID')
level1 = models.OneToOneField('Level1', db_column='Level1_ID',
parent_link=True) # parent class
class Meta:
db_table = 'Level2'
class Level3(Level2):
""" Bottom level class """
level3_id = models.AutoField(primary_key=True, db_column='Level3_ID')
level2 = models.OneToOneField('Level2', db_column='Level2_ID',
parent_link=True) # parent class
class Meta:
db_table = 'Level3'
>From the manage.py shell I add two objects to an otherwise empty database:
(InteractiveConsole)
from sc_test.models import *
# add Level1 object
top1 = Level1()
top1.name = 'Top 1'
top1.save()
# add Level3 object
bot1 = Level3()
bot1.name = 'Bot 1'
bot1.save()
# query for Level1 objects
l1 = Level1.objects.all()
l1
[<Level1: Level1 object>, <Level1: Level1 object>]
# query for Level2 objects
l2 = Level2.objects.all()
l2
[<Level2: Level2 object>]
# query for Level3 objects
l3 = Level3.objects.all()
l3
[<Level3: Level3 object>]
# Get name of first Level1 object (looks ok)
l1[0].name
u'Top 1'
# Get name of second Level1 object (looks ok)
l1[1].name
u'Bot 1'
# First Level2 object (looks ok)
l2[0].name
u'Bot 1'
# First Level3 object (!! WRONG !!)
l3[0].name
u'Top 1'
(WRONG - expected this to return u'Bot 1')
Can anyone shed some light? Specifically, does multi-table inheritance only
work with one level of subclassing? If not, is there some syntax trick I'm
missing, or is this a bug in the inheritance code?
Thanks,
Dow
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