How to use custom fields for complex django models? - django

Question

I want to define a model where a field can be one of the other defined models.
I have three models like Plane, Train and Bus. Each model has its own fields.
e.g.
class Train(models.Model):
id = models.AutoField(primary_key=True)
train_name = models.CharField(max_length=200)
date_of_journey= models.DateField()
from_station = models.CharField(max_length=4)
to_station = models.CharField(max_length=4)
class_selection = models.CharField(max_length=6, choices=class_choices)
and
class Plane(models.Model):
id = models.AutoField(primary_key=True)
date_of_journey= models.DateField()
from_airport = models.CharField(max_length=4)
to_airport = models.CharField(max_length=4)
plane_model = models.CharField(max_length=10)
class Bus(models.Model):
id = models.AutoField(primary_key=True)
date_of_journey= models.DateField()
from_city = models.CharField(max_length=100)
to_city = models.CharField(max_length=100)
I want to make a model named Trip which will have following structure:
class Trip(models.Model):
id = models.AutoField(primary_key=True)
trip_name = models.CharField(max_length=250)
reason = models.CharField(max_length=30, null=True, blank=True)
individual_journey = JourneyType(oneToManyField)
A trip can have multiple individual journeys and each journey should be either a Bus journey, a Train journey or a plane journey.

Answer 1

from django.core.exceptions import ValidationError
class JourneyType(models.Model):
bus = models.ForeignKey('Bus', blank=True, null=True)
train = models.ForeignKey('Train', blank=True, null=True)
plain = models.ForeignKey('Plain', blank=True, null=True)
def clean(self):
if not (self.bus or self.train or self.plain) or \
(self.bus and self.train) or (self.bus and self.plain) or \
(self.train and self.plain):
raise ValidationError('You should specify (only) one journey type')
def __unicode__(self):
if self.bus:
return 'Bus id={0}'.format(self.bus)
elif self.train:
return 'Train id={0}'.format(self.train)
else:
return 'Plain id={0}'.format(self.plain)
class Trip(models.Model):
# ...
individual_journey = models.ForeignKey('JourneyType')