How to pull a random record using Django's ORM?

Question

Simply use:

MyModel.objects.order_by('?').first()

It is documented in QuerySet API.

Using order_by('?') will kill the db server on the second day in production. A better way is something like what is described in Getting a random row from a relational database.

from django.db.models.aggregates import Count
from random import randint

class PaintingManager(models.Manager):
    def random(self):
        count = self.aggregate(count=Count('id'))['count']
        random_index = randint(0, count - 1)
        return self.all()[random_index]

The solutions with order_by('?')[:N] are extremely slow even for medium-sized tables if you use MySQL (don't know about other databases).

order_by('?')[:N] will be translated to SELECT ... FROM ... WHERE ... ORDER BY RAND() LIMIT N query.

It means that for every row in table the RAND() function will be executed, then the whole table will be sorted according to value of this function and then first N records will be returned. If your tables are small, this is fine. But in most cases this is a very slow query.

I wrote simple function that works even if id's have holes (some rows where deleted):

def get_random_item(model, max_id=None):
    if max_id is None:
        max_id = model.objects.aggregate(Max('id')).values()[0]
    min_id = math.ceil(max_id*random.random())
    return model.objects.filter(id__gte=min_id)[0]

It is faster than order_by('?') in almost all cases.

Here's a simple solution:

from random import randint

count = Model.objects.count()
random_object = Model.objects.all()[randint(0, count - 1)] #single random object

You could create a manager on your model to do this sort of thing. To first understand what a manager is, the Painting.objects method is a manager that contains all(), filter(), get(), etc. Creating your own manager allows you to pre-filter results and have all these same methods, as well as your own custom methods, work on the results.

EDIT: I modified my code to reflect the order_by['?'] method. Note that the manager returns an unlimited number of random models. Because of this I've included a bit of usage code to show how to get just a single model.

from django.db import models

class RandomManager(models.Manager):
    def get_query_set(self):
        return super(RandomManager, self).get_query_set().order_by('?')

class Painting(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=50)

    objects = models.Manager() # The default manager.
    randoms = RandomManager() # The random-specific manager.

Usage

random_painting = Painting.randoms.all()[0]

Lastly, you can have many managers on your models, so feel free to create a LeastViewsManager() or MostPopularManager().

The other answers are either potentially slow (using order_by('?')) or use more than one SQL query. Here's a sample solution with no ordering and just one query (assuming Postgres):

random_instance_or_none = Model.objects.raw('''
    select * from {0} limit 1
    offset floor(random() * (select count(*) from {0}))
'''.format(Model._meta.db_table)).first()

Be aware that this will raise an index error if the table is empty. Write yourself a model-agnostic helper function to check for that.

Just a simple idea how I do it:

def _get_random_service(self, professional):
    services = Service.objects.filter(professional=professional)
    i = randint(0, services.count()-1)
    return services[i]