[Zope-dev] Making PersistentList satisfy zope.schema.List

[Roger Ineichen]

Hi Paul

  

> -----Ursprüngliche Nachricht-----
> Von: zope-dev-bounces at zope.org 
> [mailto:zope-dev-bounces at zope.org] Im Auftrag von Paul Carduner
> Gesendet: Dienstag, 30. Juni 2009 21:18
> An: zope-dev
> Betreff: [Zope-dev] Making PersistentList satisfy zope.schema.List
> 
> I noticed that PersistentList and PersistentDict do not 
> satisfy zope.schema.List or zope.schema.Dict, which is rather 
> annoying.  For
> example:
> 
> class IBlogPost(Interface):
>     tags = zope.schema.List(title=u'Tags', 
> value_type=zope.schema.TextLine)
> 
> class BlogPost(Persistent):
>     implements(IBlogPost)
> 
>     tags = FieldProperty(IBlogPost['tags'])
> 
>     def __init__(self):
>         super(BlogPost, self).__init__()
>         self.tags = persistent.list.PersistentList() #aaah, 
> WrongType error...
>
> will throw a WrongType: ([], <type 'list'>) error, which is 
> especially confusing because the repr for PersistentList 
> makes it look an awful lot like a regular list.
> 
> same thing happens with PersistentDict.
> 
> I would like to modify zope.schema._bootstrapfields by 
> changing the _type attribute of the List class to (list, 
> UserList), and do the same for Dict with (dict, UserDict).  
> Then anything inheriting from UserList (including 
> PersistentList) will satisfy the schema.
> 
> Can anyone think of a reason why this would be bad?

I think it's different. If you use a zope.schem.List field
the widgets will store the list at once. This whould replace
the initial created PeristentList. (or not?)

In general if you store a simple list as attribute on a 
persistent class it's fine, everything is stored.

If you like to append or pop from this list, then yes, you
will need a PersistentList otherwise the changes in the 
list are not stored back to the DB. (right?)

Fazit,
the zope.schema.List field and the Sequence widget
is not compatible with initial PersitentList beause
the widget will probably replace the list with a
simple list.

Note, I'm not 100% sure if I'm correct. But it is at
least something which we have to make sure that this
is working.

Regards
Roger Ineichen
 
> --
> Paul Carduner
> http://www.carduner.net
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