Tml wrote:
>
> Hi,
>
> I want to make a relation such that.. i have users post some
> articles.. and can link them as relatd to other articles.
>
> I have the Article table like this:
> articles = Table('articles', metadata,
> Column('id', Integer, primary_key=True),
> Column('topic', Unicode(256), nullable=False),
> Column('rank', Integer),
> Column('content', Unicode, nullable=False),
> mysql_engine='InnoDB'
> )
>
> And I have a related articles association table like this:
>
> articles_related_articles =
> Column('article_id', Integer, ForeignKey('articles.id'),
> index=True, nullable=False),
> Column('related_id', Integer, nullable=False),
> Column('bias', SmallInteger, default=0),
> mysql_engine='InnoDB'
> )
>
You probably want to add ForeignKey('articles.id') to the related_id
column as well, and add primary_key=True to both article_id and
related_id since they identify the row.
>
> So, if article 1 is related to article 2.. then there should be two
> rows in the articles_related_articles table like:
> > 1 2 0
> > 2 1 0
>
> This is how I make the relation mapping in SA:
>
> mapper(ArticleRelatedArticle, articles_realted_articles,
> primary_key=[articles_realted_articles.c.article_id,
> articles_related_articles.c.related_id],
> properties={'article': relation(Article),}
> )
>
> assign_mapper(context, Article, articles,
> 'related': relation(ArticlesRelatedArticles,
> cascade="all, delete-
> orphan", lazy=True)
> )
>
You're using assign_mapper for one class, and plain mapper for another.
I don't know whether that might be part of the confusion.
I think I would set up the ArticleRelatedArticle mapper something like
this (untested, probably contains mistakes):
assign_mapper(context, ArticleRelatedArticle, articles_related_articles,
properties={'article': relation(Article,
primaryjoin=articles_related_articles.c.article_id==articles.c.id,
backref='related'),
'related': relation(Article,
primaryjoin=articles_related_articles.c.related_id==articles.c.id,
backref='original')})
This would add two properties to your Article class, 'related' and
'original'. Both lists would contain ArticleRelatedArticle instances,
which have 'article' , 'related' and 'bias' properties.
You might also want to look into the association proxy plugin
(http://www.sqlalchemy.org/docs/plugins.html#plugins_associationproxy)
which would make this less verbose when you aren't using the 'bias'
property.
>
> I am doing this in the shell, but its not working as expected. I dont
> see those two rows created, and related_id is always getting
> overrideen to NULL, even though I have it specified while creating the
> object.
>
> In [1]: a = Article.select()[0]
> In [3]: a.id
> Out[3]: 1L
> In [4]: b = Article.select()[1]
> In [5]: c = ArticlesRelatedArticles(article_id=a.id, related_id=b.id)
> In [6]: a.related.append(c)
> In [7]: session.flush()
> /usr/lib/python2.4/site-packages/SQLAlchemy-0.3.4-py2.4.egg/sq
> lalchemy/
> databases/mysql.py:313: Warning: Field 'related_id' doesn't have a
> default value
I think this might be because you aren't using assign_mapper for the
ArticleRelatedArticle class, so it doesn't get the magic 'assign
constructor parameters to attributes' behaviour
Hope that helps,
Simon
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