Question

i’m building a django app from an existing database. for better or worse, i have a couple of views that i would like to base my models off. they look something like this:

class Device(Model):
  id = models.IntegerField( primary_key=True, db_column='node_id' )
  name = models.CharField(max_length=127, db_column='node' )
  class Meta:
    db_table = 'node' # db view
    managed = False

class Entity(Model):
  id = models.IntegerField( primary_key=True, db_column='_id' )
  device = models.ForeignKey(Device, db_column='node_id' )
  class Meta:
    db_table = 'entity' # db view
    managed = Fase

so things work okay. however, when i try to use a template that utilises the ForeignKey it is very slow:

{% for e in entities %}
  {{ e.device.name }}
{% endfor %}

looking at the logs, it appears to be repeating queries for each ‘node_id’, and ultimately timeout out.

(of course, if i do not include e.device.name is all quick)

is there a way i can optimise this?

to be fair, the ‘entity’ view already has the name of the device as another field (node), so i could use this instead but i would like the relation to exist.

Answer 1

have you try .select_related() in your view?

entities = Entity.objects.select_related('device').filter(...)

in the other hand, if it is and old database, and no autogenerated by django, probably node_id may not be an index in the database, this will slow down a lot any JOIN.