Hello there,
Lets say I have these two models (sorry about the spanish names!) ( Django
1.8.6 and MySQL backend )
class Especialidad(models.Model):
nombre = models.CharField(max_length=250, blank=False, unique=True)
class Usuario(AbstractBaseUser):
permisosEspecialidad = models.ManyToManyField("Especialidad", blank=True)
Let u be some Usuario instance, and the following query:
u.permisosEspecialidad.all().values_list('pk',flat=True)
The actual printed query is:
SELECT `samiBackend_especialidad`.`id`
FROM `samiBackend_especialidad`
INNER JOIN `samiBackend_usuario_permisosEspecialidad` ON (
`samiBackend_especialidad`.`id` =
`samiBackend_usuario_permisosEspecialidad`.`especialidad_id` )
WHERE `samiBackend_usuario_permisosEspecialidad`.`usuario_id` = 8
As my understanding, since I'm only selecting the id field which is already
present in the intermediary table (and is also a FK), the actual join is
redundant, as I have all the info I need in this case.
So the query could work like this
SELECT `samiBackend_usuario_permisosEspecialidad`.`especialidad_id`
FROM `samiBackend_usuario_permisosEspecialidad`
WHERE `samiBackend_usuario_permisosEspecialidad`.`usuario_id` = 8
I guess this works this way because this particular case might be hard to
detect or won't be compatible with any additional query building, however, for
ForeignKey relations, this optimization is already done (If you select the
primary key from the selected model only, it wont add a join)
What would be the complications to implement this? Would it worth the effort?
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