at first glance it seems like you need just session.query
(Employee).join('managers').filter(mgr.c.age 40) ?
oh, but the issue is that managers is self-referring and needs to
be an alias ?
we have a mini feature in 0.4 so far which creates aliases, but its
not quite what you want yet, it looks like:
session.query(Employee).filter_by(['managers'], age=40)
that will create an anonymized join to the same table. this is
using get_join() with the keyword create_aliases (which you can
also try out. for your stuff, you should be working with 0.4
directly right now since youre on the cutting edge).
But also, due to recent inclement weather, we want to try to expand
out this feature from filter_by() into something that can use any
operator. this would look like...well..it would look like
Class.prop == whatever . *cue dramatic music* since multiple
class.prop==whatevers will combine together using AND semantics,
they probably will have to create aliased joins.
so yeah, everyone's wanted that since version 0.1, sonow you'll
all get it.
On Jul 11, 2007, at 4:56 PM, [EMAIL PROTECTED] wrote:
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.age40). 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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