Consider the following code:
from sqlobject import *
from sqlobject.inheritance import InheritableSQLObject
__connection__ = "sqlite:/:memory:"
def default_morx():
deriveds = list(Derived.select())
if deriveds.count():
return deriveds[0].morx
else:
return -1
class Base(InheritableSQLObject):
pass
class Derived(Base):
morx = IntCol(default=default_morx)
Base.createTable()
Derived.createTable()
d = Derived()
---
It tries to create a table class with a reasonable default value for a
column. But it raises an error because when default_morx is called,
there is a half-constructed object hanging aroung. Look at the debug
output (of a version in which default_morx doesn't do any database
access and simply returns 1):
3/QueryIns: INSERT INTO base (child_name) VALUES ('Derived')
3/QueryR : INSERT INTO base (child_name) VALUES ('Derived')
4/QueryOne: SELECT child_name FROM base WHERE id = (1)
4/QueryR : SELECT child_name FROM base WHERE id = (1)
[called default_morx here]
5/QueryIns: INSERT INTO derived (id, morx, child_name) VALUES (1, 1,
NULL)
5/QueryR : INSERT INTO derived (id, morx, child_name) VALUES (1, 1,
NULL)
6/QueryOne: SELECT morx, child_name FROM derived WHERE id = (1)
6/QueryR : SELECT morx, child_name FROM derived WHERE id = (1)
Notice that there is a row in base at the time default_morx is called,
but not a corresponding row in derived.
There are two ways I can see to deal with this:
1. Wait to create the row in base until just before the row in derived
is to be created.
2. (maybe) use transactions.
3. Have a is_fully_created boolean on every base element, and filter on
that -- then set it when done creating.
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