sqlobject-discuss

[SQLObject] Reimplements the constructor...

[<mic...@ya...>]

Hi guys!

Can I reimplement the constructor of an object. My problem is that I
have to create an article, this article can be inside a title, and can
be inside a section, I need a tree implementation for this objects:

- title 1
  - section 1
    o article 1
  - section 2
    o article 2
  o article 3

The article can be inside a section but it´s not forced, it can be
inside the title too...

I want to reimplement the constructor to know when I adding the article
in a section or in a title, so, if the user adding in a section, I can
get the title from the section, the article will always have a title,
even if it is in a section...

Is it a good idea? Thanks for any help and sorry about my poor english :)

=====
--
Michel Thadeu Sabchuk
Curitiba/PR


	
	
		
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Re: [SQLObject] Reimplements the constructor...

[Luke O. <lu...@me...>]

> I want to reimplement the constructor to know when I adding the article
> in a section or in a title, so, if the user adding in a section, I can
> get the title from the section, the article will always have a title,
> even if it is in a section...
>
> Is it a good idea? Thanks for any help and sorry about my poor english :)

I may be misunderstanding you, is article.title a ForeignKey to title that may
be NULL (when the title comes from article.section)? If so, from a database
perspective I would not duplicate the data to set article.title =
article.section.title. If section.title changes, then you need more
application code to correctly update the article title, etc.

Instead, transparently retrieve the section's title if the article has no
title:

class Article(sqlobject):
  title = ForeignKey('Title', default=None)
  section = ForeignKey('Section', default=None)
  ..

  def _get_title(self):
    storedTitle = self._SO_get_title()
    if storedTitle:
      return storedTitle
    else if self.section:
      return self.section.title
    else:
      return None

a = Article(section=aSection, ...)
a.title   # returns aSection.title
a.title = aTitle
a.title   # returns aTitle

Logic may not be exactly how you need it (which has precedence if an article
has both a title and a section?), but I would generally solve this in this
way: leave the data model clean and get the behavior I want by overriding the
properties. (See
http://www.sqlobject.org/docs/SQLObject.html#overriding-column-attributes if
the _get_columnName thing is unfamiliar.)

- Luke

Re: [SQLObject] Reimplements the constructor...

[<mic...@ya...>]

Hi Luke!

> I may be misunderstanding you, is article.title a ForeignKey to title
> that may
> be NULL (when the title comes from article.section)? If so, from a
> database
> perspective I would not duplicate the data to set article.title =
> article.section.title. If section.title changes, then you need more
> application code to correctly update the article title, etc.
> 
> Instead, transparently retrieve the section's title if the article
> has no
> title:

Hugh, oh yeah, I done something with my idea, but your idea is better,
maybe :) I coding a system to store and search my country laws, see,
the tree can be:

- law
  - title
    - section
      - subsection
        - article

or only:

- law
  - title
    - article

I done some code, and it´s working for me, look:

class Container:
  def createParentObjects(self, kw):
    _containers=['law', 'title', 'section', 'subsection', 'article']
    class_name=self.__class__.__name__.lower()
    index=_containers.index(class_name)
    containers=_containers[:index]
    # first i count how many containers was passed to the constructor
    l=[kw.has_key(x) for x in containers]
    if l.count(1)!=1:
      raise TypeError, 'You can pass only one container!'
    index=l.index(1) # there is only one index to element 1
    key=containers[index]
    # then I create the antecessors
    for container in containers[:index]:
      kw[container]=kw[key].__getattribute__(container)
    return kw

class Title(SQLObject, SubContainer):
  ...
  def __init__(self, **kw):
    SQLObject.__init__(self, **self.createParentObjects(kw))

This way I don´t need to rewrite all the constructors with the same
code, but I have the problem that I can´t change the article´s place...
I will try to implement a way using the _get_attribute idea...

thanks for all help :)

=====
--
Michel Thadeu Sabchuk
Curitiba/PR


	
	
		
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