[Grok-dev] schema.List returns a list, but is it persistent?

[Sebastian Ware]

That is true, however I would definitely call that behaviour a bug in  
schema.List. The assumption that only data manipulation is done with  
applyData sounds risky. You could get some pretty creepy bugs...

Anyway, I'll look into your suggestion.

A suggestion is to change the behaviour of applyData so that it  
returns PersistentList.

Mvh Sebastian

On 26 aug 2009, at 17.25, Leonardo Rochael Almeida wrote:

> IIRC, It is only a problem if you try to modify the list itself
> directly (like appending to, or extending the list,  or removing or
> replacing items or slices in the list). schema.List returns a new list
> for every form submission, instead of trying to alter the old list to
> include the new items. This new list is assigned to the object during
> applyData, so it will be persisted correctly.
>
> On the other hand, it's very easy to create your own class that
> extends from schema.List to return your own datatype. IIRC you only
> have to override one attribute in the subclass, and it will receive
> the same widgets as the superclass unless you register differently or
> alter the implemented interfaces.
>
> Cheers, Leo
>
> On Wed, Aug 26, 2009 at 11:56, Sebastian  
> Ware<sebastian at urbantalk.se> wrote:
>> Lists need to be implemented as PersistentList in order to be
>> automatically persisted to ZODB, however schema.List returns an
>> ordinary list and applyData seemingly stores this list as is. Isn't
>> this a big problem?
>>
>>     tags = schema.List(title=u"Content Tags",
>> value_type=schema.Choice(title=u"Content Tag",
>>            vocabulary='Content Tags'), default = [])
>>
>> Mvh Sebastian
>>
>>
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