As it turns out, this is the approach I've settled on for my Postgres Composite Type/Field implementation.
https://bitbucket.org/schinckel/django-postgres/src/6a6078d8a2cc30bfb61d093354b8228f76484a0c/postgres/fields/composite_field.py?at=default Some issues I have identified are: * it's not really possible at this stage to have something that triggers a migration operation to create the type. In practice I've just been writing that migration as a RunSQL operation, but it would be nice to have this included in the project state in some way. * There is a fair bit of duplicated code between the composite field metaclass and the django model metaclass. It's possible there are better ways to handle this. I haven't done anything with querying/lookups at this stage, but that's an exciting possible feature. I also blogged about this last year: http://schinckel.net/2014/09/24/using-postgres-composite-types-in-django/ Matt. On Friday, August 21, 2015 at 8:41:23 PM UTC+9:30, Anssi Kääriäinen wrote: > > I've been thinking how we could move forward with composite fields without > requiring too much changes in one go (large changes tend to never happen). > > It seems the first step forward would be to introduce a composite field > with the following properties: > > class Foo(models.Model): > x = models.IntegerField() > y = models.IntegerField() > point = models.CompositeField((x, y)) > > foo.point would always return a named tuplet. You could customize the > return value to a full fledged object by implementing a custom subclass of > CompositeField, but Django will not have any opinion on what should happen > when you do: > foo.x = 1 > foo.y = 2 > foo.point.x = 2 > foo.point.x == foo.x ??? > > this was one of the main concerns in the DEP. > > In addition, on query side you should be able to use > .filter(point__x__lte=...), and you should be able to select > .values('point'). We also need migrations support, and likely changes in a > lot of other places in Django. > > The draft DEPs for this feature shouldn't be used as definite resource > when implementing this feature. > > - Anssi > > On Thursday, August 20, 2015 at 6:49:11 PM UTC+3, Aron Podrigal wrote: >> >> 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, <boito...@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-develop...@googlegroups.com. >>> To post to this group, send email to django-d...@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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