Aha! I see where you're headed with this. As it turns out, the pages for a
story truly are unordered. The purpose here is to write a "Choose your own
adventure" style of story. I only included info on the problem I was
having. The missing piece of the model allows for a page to have a number
of choices that link to another page. So, the full (relevant) model is:
class Story(SQLObject):
"""
Contains the first page, and meta about a story.
"""
title=UnicodeCol(alternateID=True, length=100)
summary=UnicodeCol()
pages=MultipleJoin('Page')
first_page=ForeignKey('Page', default=None)
class Page(SQLObject):
"""
A page in a story.
"""
short_title=UnicodeCol(alternateID=True, length=20)
text=UnicodeCol()
story=ForeignKey('Story', cascade=True, default=None)
choices=MultipleJoin('Choice')
class Choice(SQLObject):
"""
A choice for a page in a story.
"""
text=UnicodeCol()
page=ForeignKey('Page', cascade=True, default=None)
choice_page=ForeignKey('Page', cascade='null', default=None)
Did this answer the "bigger problem"? Thanks for the help!
Mike
On Sun, Jan 25, 2009 at 3:01 PM, Oleg Broytmann <p...@phd.pp.ru> wrote:
> On Sat, Jan 24, 2009 at 06:07:12PM -0500, Michael LeSauvage wrote:
> > All help appreciated. The following is my data model. The idea here is
> > that a *Story* can be comprised of many pages. One, and only one, of
> those
> > pages may be the starting point of the story. I attempted to model this
> via
> > a MultipleJoin (pages in a story), a ForeignKey(to map to a single page
> for
> > a story), and a link back from the Page using a ForeignKey.
> >
> > class Story(SQLObject):
> > """
> > Contains the first page, and meta about a story.
> > """
> > title=UnicodeCol(alternateID=True, length=100)
> > summary=UnicodeCol()
> > pages=MultipleJoin('Page')
> > first_page=ForeignKey('Page', default=None) #without this, model
> works
> > #alternate, but feels like a kludge: first_page=IntCol(default=0)
> >
> > class Page(SQLObject):
> > """
> > A page in a story.
> > """
> > short_title=UnicodeCol(alternateID=True, length=20)
> > text=UnicodeCol()
> > story=ForeignKey('Story', default=None)
> >
> > I clearly don't understand what's going on under the hood.
> ...
> > Heh. OK, more detail. The *problem* is that when I generate the
> database
> > (using Turbogears, so automatic via tg-admin sql create), I get told I
> have
> > a circular dependency between Page and Story. Do I really?i
>
> Yes, you have. It is easy to see what is going on if you add '?debug=1'
> to the database URI and watch the output (or logs - I don't know where TG
> puts stdout/stderr).
>
> 1/QueryR : CREATE TABLE story (
> id SERIAL PRIMARY KEY,
> title VARCHAR(100) NOT NULL UNIQUE,
> summary TEXT,
> first_page_id INT
> )
> 1/COMMIT : auto
> 1/QueryR : ALTER TABLE story ADD CONSTRAINT first_page_id_exists FOREIGN
> KEY (first_page_id) REFERENCES page (id)
> 1/COMMIT : auto
>
> See? SQLObject created one table and tried to create a constraint - and
> failed because there is no the other table.
>
> > Is this
> > something I have to worry about?
>
> No, at least not with SQLObject - don't know about TG. There is a way in
> SQLObject to defer constraint creation until all tables are created. I will
> show you the way. Later.
>
> Now I see a problem in your model, and I consider the problem as bigger
> problem. After we fix the bigger problem it is possible the problem you
> have encountered becomes irrelevant. That's why I said 'later'.
> Let me start with a question that is actually a hint. Is you Story an
> *unordered* collection of Pages?! Before answering please remember SQL
> doesn't guarantee any order of rows until a query specifies an order.
>
> Oleg.
> --
> Oleg Broytmann http://phd.pp.ru/ p...@phd.pp.ru
> Programmers don't die, they just GOSUB without RETURN.
>
>
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