TypeError: Cannot create a consistent MRO for bases Mixin, object

Question

I am trying to add an explain() method to django QuerySet, but get the MRO error:

File ".../mixin.py", line 10, in <module>

    QuerySet.__bases__ += (QuerySetExplainMixin,)
TypeError: Cannot create a consistent method resolution
order (MRO) for bases QuerySetExplainMixin, object

the mixin and code I add it with:

from django.db import connections
from django.db.models.query import QuerySet

class QuerySetExplainMixin:
    def explain(self):
        cursor = connections[self.db].cursor()
        query, params = self.query.sql_with_params()
        cursor.execute('explain %s' % query, params)
        return '\n'.join(r[0] for r in cursor.fetchall())

QuerySet.__bases__ += (QuerySetExplainMixin,)

(credits of the mixin: https://stackoverflow.com/a/39168237/3385534 )

Answer 1

This code was written for Python 2, that's why you get a conflict in Python 3, i cannot see another way than below to set the new method on the QuerySet object :

from django.db import connections
from django.db.models.query import QuerySet

def explain(self):
    cursor = connections[self.db].cursor()
    query, params = self.query.sql_with_params()
    cursor.execute('explain %s' % query, params)
    return '\n'.join(r[0] for r in cursor.fetchall())

type.__setattr__(QuerySet, 'explain', explain)

I hope this can help you.