Using db_index with ForeignKey

Question

I just want to be on the safe side. I have this models:

class Player(models.Model):
     name = models.CharField(max_length=64, db_index=True)
     ...  

class Match(models.Model):
     date = models.DateField()
     playerA = models.ForeignKey(Player, related_name='playerA')   # neither here db_index
     playerB = models.ForeignKey(Player, related_name='playerB')   # nor here db_index
     ...

Is the usage of db_index correct? And, there is no need to add extra indexes to either playerA or playerB?

Yes, db_index won't case errors if that's what you mean, otherwise what is your question? — Maciej Gol
– Maciej Gol, Commented Nov 22, 2013 at 16:06
No errors I know, I rather want to know whether this is applied properly and will speed up filtering through playerA and playerB filters, or do I have to additionally set db_index on playerA and playerB fields in the model? — nutship
– nutship, Commented Nov 22, 2013 at 16:57

marcelor · Accepted Answer · 2013-11-23 05:13:08Z

3

Django automatically creates an index for all models.ForeignKey columns. Just run "./manage.py sql appname" and you'll see the sql statements for the creation of the indexes.

answered Nov 23, 2013 at 5:13

marcelor

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2 Comments

nutship Over a year ago

Thanks. Does it mean db_index in Player.name from my example is not needed at all?

marcelor Over a year ago

Exactly. db_index is only needed in a ForeignKey when you want to disable the automatic index creation, in that case you use db_index=False

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