Django patch for join with extra

example_use.py

# -*- coding: utf-8 -*-
from .queryset import ExtraJoinQuerySet


class ModelQuerySet(ExtraJoinQuerySet):
    def attach_useful_vote(self, user=None):
        return self.extra(select={"field": "joined_table.field"},
            join=[
                """
                JOIN (SELECT rel_id, field FROM subselect_table) AS joined_table ON table.id = joined_table.rel_id
                """
            ],
        )

queryset.py

# -*- coding: utf-8 -*-

import new
from functools import update_wrapper

from django.db.models.query import QuerySet
from django.db.models.sql.query import Query


def replace_method(method, func):
    instance = method.im_self
    method_name = method.__name__
    orig_method = method
    func.super = orig_method
    update_wrapper(func, method)
    setattr(instance, method_name, new.instancemethod(func, instance, instance.__class__))


def SQLCompiler__get_from_clause(self):
    from_, f_params = SQLCompiler__get_from_clause.super()
    if getattr(self.query, "extra_join", None):
        from_.extend(self.query.extra_join)
    return from_, f_params


class ExtraJoinQuery(Query):
    extra_join = None

    def clone(self, **kwargs):
        q = super(ExtraJoinQuery, self).clone(**kwargs)
        q.extra_join = self.extra_join
        return q

    def get_compiler(self, using=None, connection=None):
        compiler = super(ExtraJoinQuery, self).get_compiler(using=using, connection=connection)
        replace_method(compiler.get_from_clause, SQLCompiler__get_from_clause)
        return compiler


class ExtraJoinQuerySet(QuerySet):
    def __init__(self, model=None, query=None, using=None):
        super(ExtraJoinQuerySet, self).__init__(model, query, using)
        self.query = query or ExtraJoinQuery(self.model)


    def extra(self, **kwargs):
        sql_join = kwargs.pop("join", [])
        extra_join = getattr(self.query, "extra_join", None) or []
        extra_join.extend(sql_join)
        setattr(self.query, "extra_join", extra_join)
        return super(ExtraJoinQuerySet, self).extra(**kwargs)