Django: Adding Many to Many field - django

Question

I am currently struggling to assign a many-to-many field to my newly created objects. Anyone knows what I am doing wrong?
Note: I have one solution in mind which is first creating the ticket, and then afterwards trying to assign it. Might that be the way to do it?
#Create ticket_tax
assign_event = Event.objects.all()
for event in assign_event:
TicketTax.objects.create(
event=event,
name=lorem,
percentage=0.19,
)
# Create tickets
price_gross = ['40.60', '30.30', '100.40', ]
name = ['Early Bird', 'Regular Ticket', 'Last Minute Ticket', ]
assign_event = Event.objects.all().first()
assign_ticket_tax = TicketTax.objects.all().first()
for i in range(len(price_gross)):
Ticket.objects.create(
event=assign_event,
ticket_tax=assign_ticket_tax.add(),
price_gross=price_gross[i],
name=name[i],
description='ABC',
start_at='2018-05-26 18:12:58.556925+02',
end_at='2018-05-29 18:12:58.556925+02',
quantity=100,
status='On sale',
)
models.py
class TicketTax(models.Model):
event = models.ForeignKey(
Event,
on_delete=models.PROTECT,
related_name='ticket_taxes'
)
name = models.CharField(max_length=100)
percentage = models.DecimalField(
max_digits=5,
decimal_places=4
)
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
class Ticket(models.Model):
event = models.ForeignKey(
Event,
on_delete=models.PROTECT,
related_name='tickets'
)
ticket_tax = models.ManyToManyField(TicketTax, blank=True)
price_gross = models.DecimalField(
max_digits=25,
decimal_places=2
)
name = models.CharField(max_length=100)
description = models.TextField(blank=True, null=True)
start_at = models.DateTimeField()
end_at = models.DateTimeField()
quantity = models.PositiveIntegerField()
status = models.CharField(
max_length=8,
choices=TicketStatus.CHOICES
)
is_archived = models.BooleanField(default=False)
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
def __str__(self):
return self.name

Answer 1

Note: I have one solution in mind which is first creating the ticket, and then afterwards trying to assign it. Might that be the way to do it?
That is exactly correct. You can't instantiate an object and assign a M2M in one create statement--since both objects need to exist in the database. This inside the for loop should (roughly) do what your code above is trying to do:
ticket = Ticket.objects.create(
event=assign_event,
price_gross=price_gross[i],
name=name[i],
description='ABC',
start_at='2018-05-26 18:12:58.556925+02',
end_at='2018-05-29 18:12:58.556925+02',
quantity=100,
status='On sale',
)
ticket.ticket_tax.add(TicketTax.objects.all().first())