How make this special many2many fields validation using Django ORM?
- by e-satis
I have the folowing model:
class Step(models.Model):
order = models.IntegerField()
latitude = models.FloatField()
longitude = models.FloatField()
date = DateField(blank=True, null=True)
class Journey(models.Model):
boat = models.ForeignKey(Boat)
route = models.ManyToManyField(Step)
departure = models.ForeignKey(Step, related_name="departure_of", null=True)
arrival = models.ForeignKey(Step, related_name="arrival_of", null=True)
I would like to implement the following check:
# If a there is less than one step, raises ValidationError.
routes = tuple(self.route.order_by("date"))
if len(routes) <= 1:
raise ValidationError("There must be at least two setps in the route")
# save the first and the last step as departure and arrival
self.departure = routes[0]
self.arrival = routes[-1]
# departure and arrival must at least have a date
if not (self.departure.date or self.arrival.date):
raise ValidationError("There must be an departure and an arrival date. "
"Please set the date field for the first and last Step of the Journey")
# departure must occurs before arrival
if not (self.departure.date > self.arrival.date):
raise ValidationError("Departure must take place the same day or any date before arrival. "
"Please set accordingly the date field for the first and last Step of the Journey")
I tried to do that by overloading save(). Unfortunately, Journey.route is empty in save(). What's more, Journey.id doesn't exists yet. I didn't try django.db.models.signals.post_save but suppose it will fail because Journey.route is empty as well (when does this get filled anyway?). I see a solution in django.db.models.signals.m2m_changed but there are a lot of steps (thousands), and I want to avoid to perform an operation for every single of them.
