Lets say there are Employee, Engineer, Manager, etc whole tree, with
Employee in the root; all levels do have instances and its
polymorphical multitable inheritance.
Let's the Employee has attribute age - number, and manager - pointing
to some other Employee.
how to get all Employees which have a manager of age less than 40?
a straight forward sql-like thing would look like:
mgr = tableEmployee.alias()
r = session.query( Employee).select(
(tableEmployee.c.manager_id == mgr.id) & (mgr.c.age < 40) )
but can i do something smarter... e.g. some .join, .filter or
something similar?
The reason of talking about Property.get_join() here is that i am
actualy creating the above clause on the run, autoconverting from an
expression func (e.g. lambda self: self.manager.age<40). After lots
of other machinery, i am using mapper.props[key].get_join() to
guess/add the (implicit) join-conditions.
The property here is self-referential.
If the mapper (Employee) is not polymorphic - e.g. none of the other
subclasess exist - all is okay, get_join() returns something that i
ClauseAdapt to use an aliased table instead the original:
tblemployee.manager_id == tblempluyee.db_id
-> tblemployee.manager_id == tblemployee_0123.db_id
But if the mapper is polymorphic, prop.get_join() returns the
(mapper.select_table's) polymunion put on both sides:
pu_employee.manager_id == pu_employee.db_id
which my code does not recognise - its looking for tblemployee.db_id.
so the question is: is there any way to make the get_join() to not
return polymunions on _both_ sides? i see they come from some
ClauseAdaptor (many2one case) being applied...
And why it has to apply to both sides?
what i need is something like replacing only one side:
pu_employee.manager_id == tblemployee.db_id
anyway, i can roll my own get_join() replacement, i am already
workarounding the cache u have there, and having my own join_via...
(and back to the first question, the .join_to() and .join_via() finaly
use the prop.get_join() - hence i dont see how to get out of the
loop..)
btw are there any changes in these mechanics in the 0.4?
i haven't looked there yet.
ciao
svil
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