[sqlalchemy] Re: ORM ramblings 2 - and announcing some o2r wrapper
mmmh. This is about underlying base-framework of a system, equivalent in complexity to ERP. So i have unknown hierarchy of classes - be them documents, entities, whatever u fancy. And they can point to each other in an unknown way. if u want some example: DocumentA1 has some data and references other such documents (e.g. parent - in a reason-consequence chain); then DocumentA2 inherits DocumentA1 and adds some more fields to fill. More, i'm dealing with this O2R stuff over 10 years and i'm sick of specificaly write something over and over if it can be automated. But just recently i saw some light in the tunnel - SAlchemy. Therefore, all this about automating the O2R mapping. Major step? can be. i will do it. On Jan 17, 11:29 am, Paul Johnston [EMAIL PROTECTED] wrote: Hi Svil, here the case where B inherits A, and A references either A or B. i cannot get this to work.What may help everyone here, is if you can give a concrete usage example of why you want to do this. It's likely there's a way to achieve what you want to do without such major steps. Paul --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: ORM ramblings 2 - and announcing some o2r wrapper
So i have unknown hierarchy of classes - be them documents, entities, whatever u fancy. And they can point to each other in an unknown way. so, you are looking to create an application that generates python applications, basically. hm, can be interpreted this way. just add 'and interpret them on the fly' i want to use and extend the python's self-reflection - and self-modificiation - to get a sort-of self-interpretable thing, but without generating any source. Haveing proper self-reflection can auto-generate me the source - or multiple sources for multiple target environments, e.g. idl-python-python+C+html+binary. i've done that multiple times - but i want the thing to interpret itself. i know it's slower, but more flexible. if you want to use SA for that, you have to completely master SA's relationships using simple, non-dynamically generated examples first, so you can get a feel for what it does. i've done tons of this, to get where i am now. And i keep doing it. My approach is like start always a new and try with minimal possible stuff, so any thing i am using (e.g. those primary-joins) has been required in a way, (e.g. when u have multiple references, SA wants u to explicitly specify which is what). For example, i notice in your example youre trying to send in primaryjoin conditions which are already expressed in the Table objects - that already is overly complex since SA can divine simple join conditions from the tables themselves. is it errorneus to explicitly put the (correct) joins even if they could be figured out by SA? for each pattern you are trying to create dynamically, create a non-dynamic version first, get that to work, then figure out what about your dynamic thing is different from the simple version. yes, yes. so far so good, see all the sa_*py files; and when i started combining the different viewpoints - pure inheritance, pure (cyclical) references, and pure types, the thing broke. i hear theres a hot new template language called Mako that does this kind of thing.* *hehe*. good. i have done many languages before, interpretable and compileable, but now i am basing all my language creations stuff onto python - that is, using the python as syntax interpreter, and eventualy completely replacing the actual semantix; be it on-the-fly or via the objects themselves. Two examples are the StaticType declarative structure language (creatings python objects of unchangeable structure; very usable for DBs, protocols and similar must-not-change stuff), and the expr.py, which has a way to interpret python functions into Expr-trees, which then can be translated (read code-generation) into whatever, like text or sql-alchemy column expressions. It's all like using the python to build _your_ syntax tree made of your objects, and then use the objects - or some visitor - to do code-generation/ interpretation. But this is all offtopic; i could explain much-more if anyone is interested. i really _really_ want to extend the SA to be able to automaticaly do table-decomposition and mapping of an object-hierarchy. As i said, think of activemapper that also does inheritance and queries, provided just a few hints of how user exactly wants it done. So, back to the question: inheritance and referencing together? This is what stops me now; otherwise i have about 10 diff.cases that SA goes wrong, but i've found a way around so don't bother about them _now_. Also, if u can fix that repeating return obj.__dict__[key] in orm/attributes.py InstrumentedAttribute.get()... to be just return value, will be great. line 214 or so. see, i am replacing it myself, runtime (see sahack4repeatability.py ;-), but it's not nice, changing library's source on the fly ;-). Tomorrow i'll put a version stripped of all my statictype stuff, and all of the testcases (if u want so), which may seem more nice to you... all is about 1500 lines so far. have fun. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: ORM ramblings 2 - and announcing some o2r wrapper
is it errorneus to explicitly put the (correct) joins even if they
could be figured out by SA?
its not. but made your code that much harder to read
well, this case does require them :-(
which has a way to interpret python functions into Expr-trees, which
then can be translated (read code-generation) into whatever, like text
or sql-alchemy column expressions.
are you using AST for this at least ? no need to reinvent the
wheel
AST... i don't parse it, python parses it. i just replace .__eq__()
with something else.
The funny thing is, the python compiled code of some expression can be
reinterpreted in diff.ways,
e.g. def myfunc(x,y): return x100 y.startswith('big')
..
myfunc( 23, big_balls_of_fire) - will eval the func yielding
true/false, while
myfunc( Var('x'), Var('y')) - will build you an expression (procided
Var()s have operators etc defined). And even give errors - not any
syntax will fit your new semantix.
of course, theoretically, there is some AST, and some grammar, but it's
sort-a virtual...
It's all like using the python to build _your_ syntax tree made of your
objects, and then use the objects - or some visitor - to do
code-generation/ interpretation.
sounds awfully generic, when i could just write a little AST visitor...
Each time a new grammar and AST and new visitor? and teach users to
that new grammar? and testsuite preventing the huns into rome? mmh. i
did that. couple of languages per year...
Users (be them end-customers or the other-team) know their semantix
pretty well and they can cope with just about any _sensible_ easy
grammar as far as it speaks in their lingo.
oh well. my choice is - no more grammars (lowlevel) - if i can avoid
them.
As i said, think of activemapper that also does inheritance and
queries, provided just a few hints of how user exactly wants it done.
as far as querying, im guessing you
are looking for an object-query-language (which is what all the pure
ORM types seem to be desiring...but strangely they never get)
not at all. SQL, OQL and probably all them *QL frighten me. Too
extreme. Looks like academical creation with little touch to mortal
people. i am targeting what u have with columns, but applied directly
to object attributes, and used more for filtering, than real
calculations.
Practical stuff, as u said - whatever we can do, now.
So, back to the question: inheritance and referencing together?
im in the business of maintaining and developing
SQLAlchemy, and if theres a bug which you can illustrate with a
*simple* test case of around 50 lines or less, ill fix the bug,
110. can't make it less ;-)
can?
and it is about A=Employee and B=Manager, and all Employees having a
manager.
http://linuxteam.sistechnology.com/orm/sa_B_inh_A_A_ref_AB2.py
usage:
1) $ python sa_B_inh_A_A_ref_AB2.py Alink=Manager
or
2) $ python sa_B_inh_A_A_ref_AB2.py Alink=Empluyee
same 2 errors.
if of any help, i've found that if no manager (reference) is being ever
assigned, then case 1 does not crash.
-
from sqlalchemy import *
#table_inheritance, polymorphic
def case( Alink='Manager' ):
class Employee( object):
name = 'notset'
def __str__(me):
return ' '.join( [me.__class__.__name__, str(me.id),
str(me.name), getattr( me.manager, 'name', 'none') ])
class Manager( Employee ):
bonus = 'notset'
def __str__(me):
return Employee.__str__(me) + ' ' + str(me.bonus)
db = create_engine( 'sqlite:///:memory:')
meta = BoundMetaData( db)
meta.engine.echo = 0
class tables: pass
tables.Employee = Table('Employee', meta,
Column('id', Integer, primary_key=True),
Column('name', String, ),
Column('atype', String),
Column('manager_id', Integer,
ForeignKey( Alink+'.id',
use_alter=True, name='whatever1'
)
)
)
tables.Manager = Table('Manager', meta,
Column('bonus', String, ),
Column('id', Integer,
ForeignKey( 'Employee.id'),
primary_key=True,
),
)
meta.create_all()
ajoin = {
'Employee': tables.Employee.select( tables.Employee.c.atype ==
'Employee'),
'Manager': join( tables.Employee, tables.Manager,
tables.Manager.c.id ==tables.Employee.c.id),
}
Ajoin = polymorphic_union( ajoin, None )
mA = mapper( Employee, tables.Employee,
select_table=Ajoin, polymorphic_on=Ajoin.c.atype,
polymorphic_identity='Employee'
)
mA.add_property( 'manager',
relation( Alink == 'Employee' and Employee or Manager,
primaryjoin=
tables.Employee.c.manager_id==(Alink=='Employee' and tables.Employee or
tables.Manager).c.id,
lazy=True, uselist=False, post_update=True
)
)
mB = mapper( Manager,
