Mailing List Archive: Zope: Dev

z3c.form: data manager for PersistentDict/PersistentMapping

Index | Next | Previous | View Threaded

mh at gocept

Jul 11, 2009, 8:43 AM

Post #1 of 6 (791 views)
Permalink

z3c.form: data manager for PersistentDict/PersistentMapping

Hello,

z3c.form.datamanager.DictionaryField is a data manager which is
registered for fields on a dict. In its __init__ it checks whether the
data object is an instance of dict. So this data manager does neither
work for UserDict nor PersistentDict/PersistentMapping.
I'd like to change this but there are two possibilities and I'm not
sure which is the best one:

1.) Add a subclasses of DictionaryField which is registered for
UserDict and which checks whether the data object is an instance of
UserDict.
(PersistentDict and PersistentMapping are subclasses of UserDict.)

2.) Register DictionaryField for
zope.interface.common.mapping.IMapping. This might have a problem as
neither UserDict nor PersistentDict/PersistentMapping seem to provide
this interface. (Why?)

Any suggestions?

Yours sincerely,
--
Michael Howitz · mh [at] gocept · software developer
gocept gmbh & co. kg · forsterstraße 29 · 06112 halle (saale) · germany
http://gocept.com · tel +49 345 1229889 8 · fax +49 345 1229889 1
Zope and Plone consulting and development

_______________________________________________
Zope-Dev maillist - Zope-Dev [at] zope
http://mail.zope.org/mailman/listinfo/zope-dev
** No cross posts or HTML encoding! **
(Related lists -
http://mail.zope.org/mailman/listinfo/zope-announce
http://mail.zope.org/mailman/listinfo/zope )

dev at projekt01

Jul 11, 2009, 4:46 PM

Post #2 of 6 (747 views)
Permalink

Re: z3c.form: data manager forPersistentDict/PersistentMapping [In reply to]

Hi Michael

> Betreff: [Zope-dev] z3c.form: data manager
> forPersistentDict/PersistentMapping
>
> Hello,
>
> z3c.form.datamanager.DictionaryField is a data manager which
> is registered for fields on a dict. In its __init__ it checks
> whether the data object is an instance of dict. So this data
> manager does neither work for UserDict nor
> PersistentDict/PersistentMapping.
> I'd like to change this but there are two possibilities and
> I'm not sure which is the best one:
>
> 1.) Add a subclasses of DictionaryField which is registered
> for UserDict and which checks whether the data object is an
> instance of UserDict.
> (PersistentDict and PersistentMapping are subclasses of
> UserDict.)

I think this is the right solution because there are many
places in zope which do not work if a PeristentDict or
PeristentList is given instead of a simple dict or list
type.

I'm not sure but I guess not even the zope.schema validation
implementation does this part correct for list or dict fields.

class List(AbstractCollection):
"""A field representing a List."""
implements(IList)
_type = list

class Dict(MinMaxLen, Iterable):
"""A field representing a Dict."""
implements(IDict)
_type = dict

But remember, using a PersistentDict or PersitentList
field is only needed if you like to add or remove single
values from the list or dict.

Normaly you should never use a widget for PersistentList
or PeristentDict objects because the widget whould
set an empty dict or list within the new selected items
as value. Which means a PersistentDict or PersistentList
whould get replaced by a simple python type.

I'm pretty sure there are many apps out there where someone
defined a PersitentList and the first time a sequence widget
was used for set some data the PersistentList was replaced
by a simple list typ. This should not be a problem till
you will call pop or remove from this list without to marke
the persistent class itself as changed. (_p_changed = True)

As I remember, Adam Groszer suggested that we should change
the widget implementation and support to reuse the previous
class as value base if a PersistentDict or PeristentList
is used.

> 2.) Register DictionaryField for
> zope.interface.common.mapping.IMapping. This might have a
> problem as neither UserDict nor
> PersistentDict/PersistentMapping seem to provide this
> interface. (Why?)

Also the dict or list do not provide zope interfaces.
I think that's fine and we should not patch python
at this level.

Regards
Roger Ineichen

_______________________________________________
Zope-Dev maillist - Zope-Dev [at] zope
http://mail.zope.org/mailman/listinfo/zope-dev
** No cross posts or HTML encoding! **
(Related lists -
http://mail.zope.org/mailman/listinfo/zope-announce
http://mail.zope.org/mailman/listinfo/zope )

mh at gocept

Jul 13, 2009, 3:58 AM

Post #3 of 6 (736 views)
Permalink

Re: z3c.form: data manager forPersistentDict/PersistentMapping [In reply to]

Am 12.07.2009 um 01:46 schrieb Roger Ineichen:
> Hi Michael
>
>> Betreff: [Zope-dev] z3c.form: data manager
>> forPersistentDict/PersistentMapping
>>
>> Hello,
>>
>> z3c.form.datamanager.DictionaryField is a data manager which
>> is registered for fields on a dict. In its __init__ it checks
>> whether the data object is an instance of dict. So this data
>> manager does neither work for UserDict nor
>> PersistentDict/PersistentMapping.
>> I'd like to change this but there are two possibilities and
>> I'm not sure which is the best one:
>>
>> 1.) Add a subclasses of DictionaryField which is registered
>> for UserDict and which checks whether the data object is an
>> instance of UserDict.
>> (PersistentDict and PersistentMapping are subclasses of
>> UserDict.)
>
> I think this is the right solution

I think so, too, but I was not sure.

> because there are many
> places in zope which do not work if a PeristentDict or
> PeristentList is given instead of a simple dict or list
> type.
>
> I'm not sure but I guess not even the zope.schema validation
> implementation does this part correct for list or dict fields.

This is another problem. z3c.form.datamanager.DictionaryField sets the
value directly on the dict, so I'd like to use a PersistentMapping
instead of a dict to get the persistency stuff for free. I use the
PersistentMapping to store the schema values, as I need to keep them
in the session.

Yours sincerely,
--
Michael Howitz · mh [at] gocept · software developer
gocept gmbh & co. kg · forsterstraße 29 · 06112 halle (saale) · germany
http://gocept.com · tel +49 345 1229889 8 · fax +49 345 1229889 1
Zope and Plone consulting and development

_______________________________________________
Zope-Dev maillist - Zope-Dev [at] zope
http://mail.zope.org/mailman/listinfo/zope-dev
** No cross posts or HTML encoding! **
(Related lists -
http://mail.zope.org/mailman/listinfo/zope-announce
http://mail.zope.org/mailman/listinfo/zope )

mh at gocept

Jul 13, 2009, 4:21 AM

Post #4 of 6 (729 views)
Permalink

Re: z3c.form: data manager for PersistentDict/PersistentMapping [In reply to]

Am 11.07.2009 um 17:43 schrieb Michael Howitz:
> Hello,
>
> z3c.form.datamanager.DictionaryField is a data manager which is
> registered for fields on a dict. In its __init__ it checks whether the
> data object is an instance of dict. So this data manager does neither
> work for UserDict nor PersistentDict/PersistentMapping.
> I'd like to change this but there are two possibilities and I'm not
> sure which is the best one:
>
> 1.) Add a subclasses of DictionaryField which is registered for
> UserDict and which checks whether the data object is an instance of
> UserDict.
> (PersistentDict and PersistentMapping are subclasses of UserDict.)
>
> 2.) Register DictionaryField for
> zope.interface.common.mapping.IMapping. This might have a problem as
> neither UserDict nor PersistentDict/PersistentMapping seem to provide
> this interface. (Why?)

Replying to myself, as I saw on the z3c.form trunk that
DictionaryField already allows providers of
zope.interface.common.mapping.IMapping additionally to dict instances
as the storage object.
The existing solution uses the second of my possibilities, but this is
not the one which I'd like to prefer, as it does not work with
PersistentMapping out of the box.
The idea behind this change on the trunk seems to be: to allow
SessionPkgData as storage. I currently do not use it directly but use
a PersistentMapping inside SessionPkgData. But maybe this is a
sufficient solution for now.

Yours sincerely,
--
Michael Howitz · mh [at] gocept · software developer
gocept gmbh & co. kg · forsterstraße 29 · 06112 halle (saale) · germany
http://gocept.com · tel +49 345 1229889 8 · fax +49 345 1229889 1
Zope and Plone consulting and development

_______________________________________________
Zope-Dev maillist - Zope-Dev [at] zope
http://mail.zope.org/mailman/listinfo/zope-dev
** No cross posts or HTML encoding! **
(Related lists -
http://mail.zope.org/mailman/listinfo/zope-announce
http://mail.zope.org/mailman/listinfo/zope )

srichter at cosmos

Jul 13, 2009, 7:49 AM

Post #5 of 6 (740 views)
Permalink

Re: z3c.form: data manager for PersistentDict/PersistentMapping [In reply to]

On Saturday 11 July 2009, Michael Howitz wrote:
> z3c.form.datamanager.DictionaryField is a data manager which is
> registered for fields on a dict. In its __init__ it checks whether the
> data object is an instance of dict. So this data manager does neither
> work for UserDict nor PersistentDict/PersistentMapping.
> I'd like to change this but there are two possibilities and I'm not
> sure which is the best one:
>
> 1.) Add a subclasses of DictionaryField which is registered for
> UserDict and which checks whether the data object is an instance of
> UserDict.
> (PersistentDict and PersistentMapping are subclasses of UserDict.)
>
> 2.) Register DictionaryField for
> zope.interface.common.mapping.IMapping. This might have a problem as
> neither UserDict nor PersistentDict/PersistentMapping seem to provide
> this interface. (Why?)

I looked at this recently and the reason is that for containers we did not
usually want the dictionary field data manager, because we usually want the
regular instance based one.

I am okay to add PersistentDict and PersistentMapping to the list. I am
already feeling unsure about UserDict, because people might want the instance
version instead. It is better to register the adapter for the specific cases of
your application.

Regards,
Stephan
--
Entrepreneur and Software Geek
Google me. "Zope Stephan Richter"
_______________________________________________
Zope-Dev maillist - Zope-Dev [at] zope
http://mail.zope.org/mailman/listinfo/zope-dev
** No cross posts or HTML encoding! **
(Related lists -
http://mail.zope.org/mailman/listinfo/zope-announce
http://mail.zope.org/mailman/listinfo/zope )

mh at gocept

Jul 13, 2009, 11:45 PM

Post #6 of 6 (731 views)
Permalink

Re: z3c.form: data manager for PersistentDict/PersistentMapping [In reply to]

Am 13.07.2009 um 16:49 schrieb Stephan Richter:
> On Saturday 11 July 2009, Michael Howitz wrote:
>> z3c.form.datamanager.DictionaryField is a data manager which is
>> registered for fields on a dict. In its __init__ it checks whether
>> the
>> data object is an instance of dict. So this data manager does neither
>> work for UserDict nor PersistentDict/PersistentMapping.
>> I'd like to change this but there are two possibilities and I'm not
>> sure which is the best one:
>>
>> 1.) Add a subclasses of DictionaryField which is registered for
>> UserDict and which checks whether the data object is an instance of
>> UserDict.
>> (PersistentDict and PersistentMapping are subclasses of
>> UserDict.)
>>
>> 2.) Register DictionaryField for
>> zope.interface.common.mapping.IMapping. This might have a problem as
>> neither UserDict nor PersistentDict/PersistentMapping seem to provide
>> this interface. (Why?)
>
> I looked at this recently and the reason is that for containers we
> did not
> usually want the dictionary field data manager, because we usually
> want the
> regular instance based one.
>
> I am okay to add PersistentDict and PersistentMapping to the list. I
> am
> already feeling unsure about UserDict, because people might want the
> instance
> version instead. It is better to register the adapter for the
> specific cases of
> your application.

I'm fine with that, so I'm going to allow PersistentDict and
PersistentMapping in the constructor of DictionaryField and I'll add
an note why the adapter is only registered for dict and not for the
other possible data storages.

Yours sincerely,
--
Michael Howitz · mh [at] gocept · software developer
gocept gmbh & co. kg · forsterstraße 29 · 06112 halle (saale) · germany
http://gocept.com · tel +49 345 1229889 8 · fax +49 345 1229889 1
Zope and Plone consulting and development

_______________________________________________
Zope-Dev maillist - Zope-Dev [at] zope
http://mail.zope.org/mailman/listinfo/zope-dev
** No cross posts or HTML encoding! **
(Related lists -
http://mail.zope.org/mailman/listinfo/zope-announce
http://mail.zope.org/mailman/listinfo/zope )

Index | Next | Previous | View Threaded

Interested in having your list archived? Contact Gossamer Threads