Easy way to run "explain" on query sets in django

Question

It seems like it should be easy to run "explain" directly off of a queryset in Django, but I don't see anything obvious for how to do it, and "explain" is a difficult thing to search for in the docs.

score 38 · Accepted Answer · edited Feb 24 '15 at 07:22

38

Well, there seems to be nothing out there except a toolbar so I wrote my own mixin to give me an explain() method on my querysets:

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

class QuerySetExplainMixin:
    def explain(self):
        cursor = connections[self.db].cursor()
        cursor.execute('explain %s' % str(self.query))
        return cursor.fetchall()

QuerySet.__bases__ += (QuerySetExplainMixin,)

Hopefully this is useful to others.

edited Feb 24 '15 at 07:22

Tzach

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answered Jul 13 '12 at 20:57

guidoism

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Please consider opening a ticket for django project. I would love to see this builtin. – Dmitry Shevchenko Jul 14 '12 at 00:39
1

Looks useful, would be even more so with an example of how to actually use it. – szeitlin Mar 15 '16 at 21:58
Thank you! This is delicious! – mkoistinen Sep 09 '17 at 16:17
There is a ticket to add a similar feature to django now : https://code.djangoproject.com/ticket/28574 – Tom Leys Mar 13 '18 at 22:27
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How to use it ? – Bhawan Oct 18 '18 at 06:51
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Do you include this at the bottom of the file or... where? – Will Taylor Feb 19 '19 at 17:51
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This has been built into Django now https://github.com/django/django/blob/858cfd74e958b63e81657e5a9fc5f751c19e8192/django/db/models/query.py#L772-L773 – danihodovic Jul 14 '19 at 07:13

score 38 · Answer 2 · answered Oct 09 '18 at 20:51

38

QuerySet.explain(), available in Django 2.1.0 and above, is now the official way to explain queries.

answered Oct 09 '18 at 20:51

orn688

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score 19 · Answer 3 · answered Aug 26 '16 at 14:06

Just a slight modification to guidoism's answer. This prevents getting a ProgrammingError: syntax error at or near ... error caused by the parameters not being correctly escaped in the raw query:

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,)

To use, simply invoke explain() at the end of your queryset, e.g.:

print SomeModel.objects.filter(...).explain()

Easy way to run "explain" on query sets in django

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