[sqlalchemy] Re: Polymorphic and inheritance with missing children
On Feb 7, 2008, at 1:33 PM, Richard Levasseur wrote: For the syntax of it, I'd go for something like `child_obj.change_from(parent_obj)` or `child_obj = ChildClass.create_from(parent_obj)`, perhaps implicitly invoked when you do child_obj.type = parent_obj. Not sure about that last part, doesn't seem pythonic, and feels misleading. The point is to allow the child the ability to perform custom operations if need be (__change_type__?). Is the `session` part really necessary (I thought objects knew what session, if any, they were attached to?). I don't recall exactly if this is possible, but perhaps the child can have its __dict__ set to the parent's? That'd preserve any state and wouldn't require any loop-copy of attributes. the session part is introduced only in that we try not to attach lots of methods and accessors to user-defined classes. we like to leave user-defined classes as unmodified as possible which at the very least helps with the possibility of name collisions (like, if someones SA app has a change_from method already, this change would break their app). since everything else comes from session (like expunge(), refresh(), etc) this is where we like to put these things for consistency. however, thinking further about this I think how we'd actually do this would be the same way we do a primary key switch - the mapper already knows how to detect the delete of one instance and the insert of another, both with the same primary key attributes, and turn it into an update. So i would see this as an extension to that functionality, i.e.: parent = sess.query(Parent).get(1) child = Child(id=1) child.someattr = parent.someattr # copy attributes sess.delete(parent) sess.save(child) sess.flush() --~--~-~--~~~---~--~~ 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: Polymorphic and inheritance with missing children
On Feb 6, 7:01 pm, Michael Bayer [EMAIL PROTECTED] wrote: we dont yet support a seamless change of inheriting type. your best bet is to issue the SQL to the table directly which changes the polymorphic value to the new value, then inserting/deleting from the child tables as needed..then reload the object into your session (i.e. expunge() the old one first). Ok, I guess I'll play around with that at work a bit. the reason its not yet supported is because the extra steps of INSERTing and/or DELETEing in conjunction with what would normally just be an UPDATE are a little complex...also we'd have to pick an API for this (like, myobject = session.change_type(myobject, FooClass) ? not sure). but we'll get this in there sooner or later (sooner if its an urgent need for people). In our instance, its fairly important, we have about 30 different types, half of which have child tables, the other half are within the same parent table. I still need to figure out how to load the child when its record is missing, too. For the syntax of it, I'd go for something like `child_obj.change_from(parent_obj)` or `child_obj = ChildClass.create_from(parent_obj)`, perhaps implicitly invoked when you do child_obj.type = parent_obj. Not sure about that last part, doesn't seem pythonic, and feels misleading. The point is to allow the child the ability to perform custom operations if need be (__change_type__?). Is the `session` part really necessary (I thought objects knew what session, if any, they were attached to?). I don't recall exactly if this is possible, but perhaps the child can have its __dict__ set to the parent's? That'd preserve any state and wouldn't require any loop-copy of attributes. --~--~-~--~~~---~--~~ 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] Elixir 0.5.1 released!
I am very pleased to announce that version 0.5.1 of Elixir (http://elixir.ematia.de) is now available. As always, feedback is very welcome, preferably on Elixir mailing list. This is mostly a bug fixes release (especially for people using inheritance), but we have also a few minor new features, including a new plugin for managing entities as (ordered) lists, enhanced support for custom base classes and an alternate (nicer) syntax to define synonym properties. The full list of changes can be seen at: http://elixir.ematia.de/trac/browser/elixir/tags/0.5.1/CHANGES What is Elixir? - Elixir is a declarative layer on top of the SQLAlchemy library. It is a fairly thin wrapper, which provides the ability to create simple Python classes that map directly to relational database tables (this pattern is often referred to as the Active Record design pattern), providing many of the benefits of traditional databases without losing the convenience of Python objects. Elixir is intended to replace the ActiveMapper SQLAlchemy extension, and the TurboEntity project but does not intend to replace SQLAlchemy's core features, and instead focuses on providing a simpler syntax for defining model objects when you do not need the full expressiveness of SQLAlchemy's manual mapper definitions. Mailing list http://groups.google.com/group/sqlelixir/about -- Gaëtan de Menten http://openhex.org --~--~-~--~~~---~--~~ 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] self referential query with order_by
I have a self referential hierarchy structure in a table that I have
mapped with SA 0.4. What I would like to do is query the table given a
node, and find its grandchildren based on some criteria in both the
child and grandchildren nodes. In SQL I would do:
SELECT * FROM nodehierarchy AS grandparent
JOIN nodehierarchy AS parent ON parent.parentuid = grandparent.uid
JOIN nodehierarchy AS child ON child.parentuid = parent.uid
WHERE grandparent.uid = some_value
AND parent.type=different_value
AND child.type=another_value
ORDER BY parent.name, child.name;
Following the third example from
http://www.sqlalchemy.org/docs/04/mappers.html#advdatamapping_relation_selfreferential_query
I have the following:
grandchildren = session.query(Node).filter(Node.c.type==var1).\
join('Parent', aliased=True).filter(Node.c.type==var2).\
join('Parent',aliased=True,
from_joinpoint=True).filter(Node.uid==var3).all () #
order_by(Node.Parent.name, Node.name).all()
grandchildren.sort (key=lambda i: (i.Parent.name,i.name))
However the commented out order_by() doesn't work I get AttributeError:
'InstrumentedAttribute' object has no attribute 'name'
As you can see I am currently sorting client side.
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[sqlalchemy] Re: Polymorphic and inheritance with missing children
Ok, so I've been looking into getting it to work when the child record doesn't exist. I haven't had much luck. I wrote a stub mapper extension for translate_row and populate_instance, but it doesn't seem to be called when it goes to fetch the information for the child row. mapper(Parent, parents, polymorphic.) mapper(Child, children, extension=MyExtension(def translate_row, def populate_instance)) query(Parent) my translate_row called my populate_instance called mapper.py:_get_poly_select_loader, the first inline post_execute is called to fetch the data: row = selectcontext.session.connection(self).execute(statement, params).fetchone() self.populate_instance(selectcontext, instance, row, isnew=False, instancekey=identitykey, ispostselect=True) Shouldn't translate_row be called before then? In the working case (child exists), neither of my extension methods are called, too. It makes sense that they would only be called once per result, but in this case a single result is actually 2 records fetch separately. --~--~-~--~~~---~--~~ 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 -~--~~~~--~~--~--~---
