Easy way to run “explain” on query sets in django

问题

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.

回答1:

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.

回答2:

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()

回答3:

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

来源：https://stackoverflow.com/questions/11476664/easy-way-to-run-explain-on-query-sets-in-django