Hi Hansel, Might be missing the point, but... If you're looking to reference the individual fields, can you leverage the Postgres JsonField's key lookup functionality? As per https://docs.djangoproject.com/en/1.11/ref/contrib/postgres/fields/#key-index-and-path-lookups
A quick bit of code inspection appears to show Django's ORM assembling the necessary SQL for you: https://github.com/django/django/blob/b29c6c96c738bd7250a408b079dd8a4d4657849a/django/contrib/postgres/fields/jsonb.py#L90 At very least, this might give you somewhere to start from - eg: wrapping this capability, or implementing your own get_transform for the field may allow you to build the JSON paths manually if you're finding it's not suitable. Hope that helps... James On Fri, 27 Oct 2017 at 05:43 Hansel Dunlop <han...@interpretthis.org> wrote: > Thank you Kuba! That's interesting. Good to know it's possible . If not, > perhaps, advisable. I imagine my translated fields could register the > models they're on and "as_sql" could do a quick lookup to see if we were > referencing any of them in the particular query. > > I have looked at existing alternatives. In fact we're using > django-modeltranslation currently. The API of which I think is great. But I > don't want to continue to scale it because of the number of extra columns > it's adding to the database and the size and ugliness of the queries it's > generating. If we have a model with 10 translated fields and 160 translated > languages we would have just hit postgresql's 1600 column limit and the > queries themselves would be > 10KB. Not to mention the number of extra > database migrations we would have generated to get there. > > The APIs for django-hvad and django-parler both seem to have slightly > different goals. I want to completely avoid talking about translations in > my general code. Set the language for a request once based on the headers > it provides. And return an api response where any localised fields are > provided in that language without modifying any view or serializer code. > > I have a custom TranslatedField that achieves these goals, quite simply. > And it's good to know I can make further optimisations to it should I need > to. > > > On Fri, Oct 27, 2017 at 12:03 AM, Kuba <kuba.janos...@gmail.com> wrote: > >> Hi Hansel, >> >> >> On 26 October 2017 at 18:52, Hansel Dunlop <han...@interpretthis.org> >> wrote: >> >>> Hi all, >>> >>> So I just got a notification from Stackoverflow that this question - >>> https://stackoverflow.com/questions/46804936/custom-django-field-type-with-modified-column-look-up-in-select-part >>> - was just awarded the tumbleweed badge (no, votes, no answers, and no >>> views)... >>> >> >>> So throwing this open to the wider community here. I do suspect there is >>> no way of doing this in Django. But I wish there was. Because I'm trying to >>> create a custom translation infrastructure and it would help if I could >>> just return the actual text in the query rather than the whole blob of json. >>> >> >> >> so just regarding this part: *Does Django have any hooks that let me >> dynamically change the 'SELECT' part of the query?* >> >> Writing custom SQL backend (with only one custom part - the compiler) >> would be one relatively "easy" way to do that. As weird as it sounds it >> would take one method to override and mess up with. >> django.db.models.sql.compiler.SQLCompiler.as_sql is your friend. You'd need >> to find a clever way to figure out if given compiled sql query is the one >> you're interested in and only then alter it, to avoid performance >> penalties. I'm not sure it's a good idea, but it is possible. Of course >> it's quite deep in internals so passing any custom stuff there would be >> anyway kinda "threadlocal-magical". >> >> Regarding translations, just curious: have you considered django-hvad / >> django-parler? >> >> Cheers, >> Jakub >> >> >> >>> >>> I mean maybe I could on the fly modify the db_column value. But would >>> that be thread safe? Doubt it. >>> >>> -- >>> >>> Hansel >>> >>> _______________________________________________ >>> python-uk mailing list >>> python-uk@python.org >>> https://mail.python.org/mailman/listinfo/python-uk >>> >>> >> >> _______________________________________________ >> python-uk mailing list >> python-uk@python.org >> https://mail.python.org/mailman/listinfo/python-uk >> >> > > > -- > > Hansel > _______________________________________________ > python-uk mailing list > python-uk@python.org > https://mail.python.org/mailman/listinfo/python-uk >
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