Hi Massimo,
this is a very promising feature !
My quick two cents:
Why not turn this generic by replacing the 'body' field with a 'node_name'
field and add an attribute node table ?
For example:
db.define_table('node',
Field('parent_id','reference node'),
Field('node_name','string'))
and
db.define_table('attribute',
Field('node_id','reference node'),
Field('key','string'),
Field('value','string'))
The tree definition above needs to create a fake root node, forces a given
node to belong to only one parent node and is efficient when traversing
tree from leaf to trunk but for a given node the children node(s) are
unknown.
The tree definition below could be a better solution, but may require extra
work to keep references integrity especially when moving or deleting nodes:
db.define_table('node',
Field('parent_id','list:reference node'),
Field('child_id','list:reference node'), // sorting this
may permit to manage siblings
Field('node_name','string'))
Eventually a delirious attribute table evolution might be to have a type
field (string, integer, reference, ....) and validator per node attribute,
but I can't figure out how to do that :)
Thanks again for this new feature,
Mirko,
PS: btw, no plans for DAL ZODB support ?
http://www.zodb.org/en/latest/documentation/guide/introduction.html
On Monday, October 21, 2013 5:57:00 AM UTC+2, Massimo Di Pierro wrote:
>
> It is a recurrent problem that is displays tree-like structures like
> threaded comments. For example:
>
> db.define_table('post',
> Field('parent_id','reference post'),
> Field('body'))
>
> where each comment has a body and a parent_id (parent_id==None for the
> root comment(s))
> We can populate the comments with some dummy data:
>
> def make_up_data():
> import random, uuid
> ids = [None]
> for k in range(100):
> ids.append(db.post.insert(parent_id=random.choice(ids),
> body=str(uuid.uuid4())))
> if k==0:
> ids.pop(None)
> if db(db.post).isempty(): make_up_data()
>
> The new feature in trunk allows you to select the comments are organized
> them into trees.
>
> roots = db(db.post).select().as_trees()
>
> This returns a list of parent nodes. Each not stores its own children,
> recursively.
>
> Now you can print them all using a tree traversal:
>
> def show(row,n=0):
> return ' '*n+row.body+'\n'+''.join(show(c,n+1) for c in
> row.children)
> print show(roots[0])
>
> Notice you can specify the name of the parent field:
>
> roots = db(db.post).select().as_trees(parent_name="parent_id")
>
> Please let me know if you think this can be improved.
>
>
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