[sqlalchemy] Re: class-object-like attribute lookup
Karl Guertin schrieb: Looks like you want recursive single table inheritance [1]. It doesn't need to be recursive, just a two-level parent-child relation. And I don't want to add any columns, so I was thinking that table inheritance is not the right approach, but I'm not sure about that. Chris --~--~-~--~~~---~--~~ 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: class-object-like attribute lookup
On 1/25/07, Christopher Arndt [EMAIL PROTECTED] wrote: It doesn't need to be recursive, just a two-level parent-child relation. And I don't want to add any columns, so I was thinking that table inheritance is not the right approach, but I'm not sure about that. I was thinking that you could check parent_id for null or not null and map that way, but it doesn't look like the polymorphic mapper can handle that. Ah well. --~--~-~--~~~---~--~~ 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: class-object-like attribute lookup
You could do this in a single join using COALESCE on the fallback columns. Rick On 1/25/07, Karl Guertin [EMAIL PROTECTED] wrote: On 1/25/07, Christopher Arndt [EMAIL PROTECTED] wrote: It doesn't need to be recursive, just a two-level parent-child relation. And I don't want to add any columns, so I was thinking that table inheritance is not the right approach, but I'm not sure about that. I was thinking that you could check parent_id for null or not null and map that way, but it doesn't look like the polymorphic mapper can handle that. Ah well. --~--~-~--~~~---~--~~ 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: class-object-like attribute lookup
COALESCEwow i need to read some SQL books again... :) On Jan 25, 2007, at 11:17 AM, Rick Morrison wrote: You could do this in a single join using COALESCE on the fallback columns. Rick On 1/25/07, Karl Guertin [EMAIL PROTECTED] wrote: On 1/25/07, Christopher Arndt [EMAIL PROTECTED] wrote: It doesn't need to be recursive, just a two-level parent-child relation. And I don't want to add any columns, so I was thinking that table inheritance is not the right approach, but I'm not sure about that. I was thinking that you could check parent_id for null or not null and map that way, but it doesn't look like the polymorphic mapper can handle that. Ah well. --~--~-~--~~~---~--~~ 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: class-object-like attribute lookup
Dude, you should be WRITING them! On 1/25/07, Michael Bayer [EMAIL PROTECTED] wrote: COALESCEwow i need to read some SQL books again... :) On Jan 25, 2007, at 11:17 AM, Rick Morrison wrote: You could do this in a single join using COALESCE on the fallback columns. Rick On 1/25/07, Karl Guertin [EMAIL PROTECTED] wrote: On 1/25/07, Christopher Arndt [EMAIL PROTECTED] wrote: It doesn't need to be recursive, just a two-level parent-child relation. And I don't want to add any columns, so I was thinking that table inheritance is not the right approach, but I'm not sure about that. I was thinking that you could check parent_id for null or not null and map that way, but it doesn't look like the polymorphic mapper can handle that. Ah well. --~--~-~--~~~---~--~~ 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: class-object-like attribute lookup
On Jan 25, 2007, at 9:35 AM, Christopher Arndt wrote:
As you can see 'parent_id' is a self-referencing FK to the
bookmarks table. The
idea now is to allow users to have their own copies of mapped
'Bookmark'
objects, that are a sort of child of an existing 'Bookmark' object
and allow
them to overwrite certain columns like e.g. 'title' and
'description'. But if
the column is NULL, it should be looked up in the parent object/
row. Sort-of
like in class/object attributes in Python classes.
i almost understand what you mean, but what column is NULL? if the
parent_id column is null, then youre the topmost parent bookmark
(i.e. no parent to be looked up). if the owner_id column is null,
no user points to this bookmark.
it sounds like basically many users would point to a common record in
the bookmark table, and for those users who want to override
certain attributes, a new copy of that bookmark object is made for
them and a new record with their owner_id gets inserted into the
database. is that it ?
ohyou mean, yes, they have their local bookmark copy, but if an
attribute is NULL, it goes up to the parent. right:
class Bookmark(object):
def _get_inherited_attr(self, key):
if getattr(self, _ + key) is None:
if self.parent is not None:
return getattr(self.parent, _ + key)
return None
title = property(lambda self:self._get_inherited_attr(title),
lambda self, value:self._title=value)
description = property(lambda self:self._get_inherited_attr
(description), lambda self, value:self._description=value)
url = property(lambda self:self._get_inherited_attr(url),
lambda self, value:self._url=value)
mapper(Bookmark, bookmark_table, properties={
'parent':relation(Bookmark, remote_side=bookmark_table.c.id),
'_title':bookmark_table.c.title,
'_description':bookmark_table.c.description,
'_url':bookmark_table.c.url
})
the above can be made more concise by creating your own property
class, i.e. a class that has __get__() and __set__() methods, instead
of using the property() function.
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