[SQLObject] InheritableSQLObject and ForeignKeys: unpredictable behaviour.

[Alan F. <ala...@gm...>]

Hello, I think there's an unpredictable behaviour in
InheritableSQLObject and FKs handling. Whenever you define a FK in any
'standard' SQLObject, you get a 'foreignkeyID' attribute returning the
same result as getattr(SQLObject,'foreignkey').id but, I think (I didn't
check actual debug output), skipping an additional SELECT query from the
DB ( I think the 'foreignkeyID' attribute simply returns the value in
the column from the table, while the other method actually queries the
DB for the record in the referred table and returns the id - same
result, longer execution ).

Whenever you try doing this with a child InheritableSQLObject, you get
an error. Trying to fetch the result from the parent table does no good,
since SQLObject returns a child instance anyway, if there's any.

I think this is a 'gotcha' - i was widely using such shortcut in my
software, and now I'm forced to redesign it :-(.

If the 'foreignkeyID' version is 'for internal use only' by the
software, it should be prefixed by _, but I think it would be a great
improvement to have it working as it is now for InheritableSQLObject as
well.

#begin inheritablefks.py
from sqlobject import *
from sqlobject.inheritance import InheritableSQLObject

__connection__= #fill in your connection URI

class Referred(SQLObject):
    referred=IntCol()

class Standard(SQLObject):
    standard=IntCol()
    referred=ForeignKey('Referred')

class Parent(InheritableSQLObject):
    parent=IntCol()
    referred=ForeignKey('Referred')

class Child(Parent):
    child=IntCol()


Referred.createTable()
Standard.createTable()
Parent.createTable()
Child.createTable()

ref=Referred(referred=1)
std=Standard(standard=2,referred=ref)
child=Child(parent=3,child=4,referred=ref)

print std.referredID
try:
    print child.referredID
except AttributeError:
    print 'Child:No such attribute'

parent=Parent.get(child.id)

try:
    print parent.referredID
except AttributeError:
    print 'Parent: No such attribute'
#end inheritablefks.py




-- 
Alan Franzoni <ala...@gm...>
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