Django custom for complex Func (sql function)

Question

In the process of finding a solution for Django ORM order by exact, I created a custom django Func:

from django.db.models import Func

class Position(Func):
         


        

Answer 1

basis on the John Moutafis ideas, final function is (inside the __init__ method we use Values for safety result.)

from django.db.models import Func, F, Value
from django.db.models.functions import Lower


class Instr(Func):
    function = 'INSTR'

    def __init__(self, string, substring, insensitive=False, **extra):
        if not substring:
            raise ValueError('Empty substring not allowed')
        if not insensitive:
            expressions = F(string), Value(substring)
        else:
            expressions = Lower(string), Lower(Value(substring))
        super(Instr, self).__init__(*expressions)

    def as_postgresql(self, compiler, connection):
        return self.as_sql(compiler, connection, function='STRPOS')