Have a look at [1] it is a composite field implementation. [1] https://groups.google.com/forum/m/#!msg/django-developers/MZUcOE6-7GY/sZkBaHvC8wgJ [2] https://github.com/django/deps/blob/master/draft/0191-composite-fields.rst [3] https://github.com/django/deps/blob/master/draft/0192-standalone-composite-fields.rst On Aug 20, 2015 10:31 AM, <boitole...@gmail.com> wrote:
> > > Le mardi 18 août 2015 01:36:28 UTC+2, Tim Graham a écrit : >> >> I think the general idea is captured in ticket #5929 -- Allow Fields to >> use multiple db columns (complex datatypes). Is that the gist of your >> proposal? >> > > Thank you for this link! It seems to discuss the same end result as what I > tried to present in my first message: the ability to have a single > models.Field managing an arbitrary number of DB columns under the hood. > > The proposed approach is perhaps a bit different: if I understood the > ticked correctly, it proposes to change the base Field class to make it > possible, when deriving from it, to manage one or several DB columns. My > first idea was more to mimic the composite pattern implementation already > in use with forms.MultiValueField: > * The models.Field *leaf* classes would still manage a single DB column. > * Introduce a models.MultiField class, which is a container of > models.Field classes (be it leaf classes or other MultiField classes). This > container would address the multiple columns indirectly, through the > interface of the composing fields. And, to the eyes of the rest of the > code, it would behave as a normal field, notably offering the to_python() > feature, hiding the composition in its implementation details. > > I did not take time yet to try and assemble a prototype of this idea; In > fact, I first wanted to confirm if such approach has not already been > rejected in the past, before investing work in it ;) > > Does it sound like a feasible/interesting idea ? Or is there a good reason > not to do it / too many obvious technical complications that I did not > foresee ? > > Thank you for reading, > Ad > > >> https://code.djangoproject.com/ticket/5929 >> >> On Monday, August 17, 2015 at 5:11:01 AM UTC-4, boito...@gmail.com wrote: >>> >>> Hi, >>> >>> While implementing our collection management system based on Django, >>> we are always excited by the extensibility of the framework. >>> Most recently, we were exposed to the *forms.MultiValueField* and* >>> widgets.MultiWidget*, that seem to offer composition capacities to >>> users of the *form* and *widget* layers. Yet, we did not find any >>> equivalent in the *model* layer, which seemed a bit surprising knowing >>> that those 3 layers can work hand-in-hand very easily >>> >>> Is there a rationale to prevent implementation of such a >>> models.MultiField class ? It could be a wrapper around the composite >>> pattern in the *model* layer, allowing users to easily define custom >>> models.Field that would leverage existing *models.Field* classes, by >>> assembling them for specific purposes (while maximizing reuse). >>> >>> ---- >>> >>> This question was also raised in Stack Overflow here: >>> http://stackoverflow.com/q/32014748/1027706. Below is a summary of the >>> question's example motivating such feature request: >>> >>> Imagine we want to store partial date in the DB (i.e., a date that is >>> either complete , or just month+year, or just year). We could model it in >>> the models layer using a *models.DateField* + a *models.CharField* >>> (this last field storing whether the date is complete, or month+year, or >>> just year). >>> >>> Now, if we move to the forms layer, let's say we want a custom >>> validation step that when a date is partial, the "unused" part of the >>> DateField must be the value '1'. Because a *ModelForm* automatically >>> maps one *forms.Field* to each *models.Field*, this constraint would >>> require a cross-field validation. >>> >>> On the other hand, if there was a *models.MultiField*, one could define >>> a *PartialDate* class to inherit from said *MultiField*. It would then >>> be seen by other layers as a single *models.Field* (implemented by >>> aggregating two other *models.Field*, but that would be an >>> implementation detail hidden from other layers). In *ModelForm*, this >>> single *models.Field* would map a to a single custom* forms.Field* (probably >>> deriving from *forms.MultiValueField*), and the validation step above >>> would not need to be a cross-field validation anymore (more precisely, this >>> validation could now happen at the *forms.MultiValueField* level, >>> instead of the *Form* level). With this approach, it seems that the >>> *models.PartialDate* and the *forms.PartialDate* could be written once, >>> and reused in as many models and applications as possible, thus respecting >>> Django's DRY philosophy. >>> >>> ---- >>> >>> Could a prototype implementation of such composite model field be of >>> interest ? >>> >>> >>> -- > You received this message because you are subscribed to the Google Groups > "Django developers (Contributions to Django itself)" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to django-developers+unsubscr...@googlegroups.com. > To post to this group, send email to django-developers@googlegroups.com. > Visit this group at http://groups.google.com/group/django-developers. > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-developers/ca502bdb-da07-4ccc-a60e-5eb537cd80ac%40googlegroups.com > <https://groups.google.com/d/msgid/django-developers/ca502bdb-da07-4ccc-a60e-5eb537cd80ac%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. 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