django - When I try to add a deck of cards to my database i get: Integrity error decks_deck.cardID_id may not be NULL. What am I doing wrong? -

i made models this:

from django.db import models   class attribute(models.model):     idattr= models.charfield(primary_key=true, max_length=40)     description= models.charfield(max_length=40)     def __str__(self):         return self.description       class cardtype(models.model):     idcardtype= models.charfield(primary_key=true, max_length=40)     description= models.charfield(max_length=40)     def __str__(self):         return self.description  class monstertype(models.model):     idmonstertype= models.charfield(primary_key=true, max_length=40)     description= models.charfield(max_length=40)     def __str__(self):         return self.description   class cardclass(models.model):     idcardclass= models.charfield(primary_key=true, max_length=40)     description= models.charfield(max_length=40)     def __str__(self):         return self.description   class card(models.model):     idcard= models.charfield(primary_key=true, max_length=40)     name= models.charfield(max_length=40)     description= models.charfield(max_length=100)     attrid= models.foreignkey(attribute)     cardtypeid= models.foreignkey(cardtype, null=true, blank=true)     monstertypeid= models.foreignkey(monstertype, null=true, blank=true)     cardclassid= models.foreignkey(cardclass)     def __str__(self):         return self.name      class deck(models.model):     iddeck= models.charfield(primary_key=true, max_length=40)     name= models.charfield(max_length=40)     cardid= models.manytomanyfield(card)      def __str__(self):         return self.name 

however when fill in required fields in database error cardid saying may not null.

the card class used add cards , deck should show list of added cards throught cardid field, does. fill in other fields , select cards want add deck. after clicking save error mentioned above.

i've read various posts on site , read djago documentation, haven't been able solve it. appreciate get.

can use this

id = models.autofield(primary_key=true)