model grandchild joins to top instead of the middle first

[phowe]

I create a blank app with these models:

class Base( models.Model ):
  b_id = models.AutoField( primary_key=True )
  b_desc = models.CharField( max_length=100 )

class Middle( Base ):
  m_id = models.AutoField( primary_key=True )
  m_desc = models.CharField( max_length=100 )

class Top( Middle ):
  t_id = models.AutoField( primary_key=True )
  t_desc = models.CharField( max_length=100 )

I run this:

d = Top.objects.all()
print d.query
SELECT "example2_base"."b_id", "example2_base"."b_desc", "example2_middle"."base_ptr_id", "example2_middle"."m_id", "example2_middle"."m_desc", "example2_top"."middle_ptr_id", "example2_top"."t_id", "example2_top"."t_desc"
  FROM "example2_top"
  INNER JOIN "example2_base" ON ("example2_top"."middle_ptr_id" = "example2_base"."b_id")
  INNER JOIN "example2_middle" ON ("example2_top"."middle_ptr_id" = "example2_middle"."m_id")

The INNER JOIN links the Base model to the Top, I would expect the joins to look like this:

 INNER JOIN "example2_middle" ON ("example2_top"."middle_ptr_id" = "example2_middle"."m_id")
 INNER JOIN "example2_base" ON ("example2_middle"."base_ptr_id" = "example2_base"."b_id")

As long as the id's in the 3 tables stay in sync, the issue is not noticed, however if one of the id's gets incremented a head of one of the others, the query returns the wrong base parts of the model.

I found this while running 1.2, I also downloaded the 1.4 alpha and noticed the same results.

[Anssi Kääriäinen]

I can see your point here. There is no guarantee that b_id == m_id which is assumed by the generated code. The bug is not present if you don't have separate primary keys for each of the models. In general I would suggest not defining the additional primary keys, I can't see them serving any purpose.

I am marking this as accepted, but I don't think this will be high on the list of things to fix, just because your use case (each model having a new primary key) isn't that common.

[phowe]

Thanks for the pointer, I should be able to adapt my code in that direction.

Just an FYI I have noticed if I take all of the *_id fields, I this for the joins:

INNER JOIN "example3_base" ON ("example3_top"."middle_ptr_id" = "example3_base"."id")
INNER JOIN "example3_middle" ON ("example3_top"."middle_ptr_id" = "example3_middle"."base_ptr_id")

I guessing that the middle_ptr_id field in the top table should have been created as base_ptr_id (there is no middle id any more).

[phowe]

fixed by #18174

[Tim Graham]

Marking as duplicate of #18174 per comment 3.