Add support for Table Function Model.

[Petr Přikryl]

Opening based on discussion here ​https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/django-developers/3HC3twc_pGI/HWzlwAjoAQAJ

Motivation

I have some complex database View with CTEs. The problem here is that I need only few records from that View. But the View is always evaluated completely and limited after that. The solution here is re-writing View as Table Function ​https://stackoverflow.com/questions/11401749/pass-in-where-parameters-to-postgresql-view.

Proposed usage

class MyTableFunctionModel(Model)
    parent = models.ForeignKey('self', on_delete=models.DO_NOTHING)

    class Meta:
        db_table = 'my_function'
        table_function_args = [
            TableFunctionArg(name='foo', required=False),
            TableFunctionArg(name='bar', required=False),
        ]


MyTableFunctionModel.objects.table_function(foo=1, bar='value', parent__foo=2, parent__bar='cha')

# SELECT ... FROM my_function(1, 'value') T1 JOIN my_function(2, 'cha') T2 ON T1.id = T2.parent_id

Here are some my working experiments ​https://gist.github.com/petrprikryl/7cd765cd723c7df983de03706bf27d1a

[Mariusz Felisiak]

Thanks for this proposition, however it's quite niche IMO. Moreover if we want to support something in Django we need to support it fully and I can see here many caveats that can cause maintenance burden, e.g. migrations or lack of support on some databases.

It sounds like a third-party database backend is the best way to proceed.