we do have a self-referential example using ActiveMapper:
http://www.sqlalchemy.org/trac/browser/sqlalchemy/trunk/test/ext/
activemapper.py#L223
i think the problem you have is that youre putting "comment_id",
which is the name of a table column, as the backref name. it should
be the name of a relationship that will give you the parent Comment
object, such as "parent_comment".
On Jul 30, 2006, at 2:41 PM, Graham Higgins wrote:
> Hi,
>
> I've encountered a couple of instances of a specific SQL design
> pattern, aimed at mimicking a linked list (of comments and sub-
> comments to blog entries) and I'd just like to check that the pattern
> is known not to be supported in ActiveMapper.
>
> Michael Bayer describes the pattern as "handling a hierarchical
> relationship on itself", and in his implementation, "contains a lazy
> reference both to its parent comment and its list of child comments."
>
> 1st instance is reflog's Turboblog, uses SQLObject and handles the
> mapping explicitly:
>
> class Comment(SQLObject):
> class sqlmeta:
> table = "turboblog_comment"
> [...]
> parent_id = IntCol(default=-1)
> sub_comments = RelatedJoin("Comment",joinColumn="parent_id")
>
> 2nd instance is Michael Bayer's zblog, uses SQLAlchemy, mapping is
> handled via foreign_key:
>
> comments = Table('comments', metadata,
> Column('comment_id', Integer, primary_key=True),
> [...]
> Column('parent_comment_id', Integer, ForeignKey
> ('comments.comment_id')),
> )
>
> augmented with:
>
> # comment mapper. This mapper is handling a hierarchical
> relationship on itself, and contains
> # a lazy reference both to its parent comment and its list of child
> comments.
> mapper(Comment, tables.comments, properties={
> 'id':tables.comments.c.comment_id,
> 'post':relation(Post, lazy=True, backref=backref('comments',
> cascade="all, delete-orphan")),
> 'user':relation(user.User, lazy=False, backref=backref
> ('comments', cascade="all, delete-orphan")),
> 'parent':relation(Comment,
> primaryjoin=tables.comments.c.parent_comment_id==tables.comments.c.com
> me
> nt_id, foreignkey=tables.comments.c.comment_id, lazy=True,
> uselist=False),
>
> I've tried both approaches in ActiveMapper, neither of which seem to
> work (but I'm a newbie w.r.t sqlalchemy):
>
> class Comment(ActiveMapper):
> class mapping:
> __table__= "comment"
> comment_id = column(Integer, primary_key=True)
> [...]
> parent_id = column(Integer, default=-1)
> sub_comments = one_to_many("Comment", colname="parent_id",
> backref="comment_id")
>
> ArgumentError: Cant find any foreign key relationships between
> 'comment' and 'comment'
>
> class Comment(ActiveMapper):
> class mapping:
> __table__= "comment"
> comment_id = column(Integer, primary_key=True)
> [...]
> parent_id = column(Integer,
> foreign_key="comment.comment_id", index=True)
> sub_comments = one_to_many("Comment", colname="parent_id",
> backref="comment_id")
>
> AttributeError: 'ColumnProperty' object has no attribute
> '_get_target_class'
>
> I'm thinking that this design pattern may be outside the intentions
> of ActiveMapper --- Michael Bayer has already indicated that
> "ActiveMapper is just giving you a thin layer of "shortcut" on top of
> things".
>
> (It's not that it can't be done with an explicit Table+mapper, it's
> just that I'm lazy and prefer to work at the highest level of
> abstraction available if possible.)
>
> Cheers,
>
> Graham Higgins.
>
>
>
>
>
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