django - UNIQUE CONSTRAINED FAILED error - django

Question

This is what my models.py looks like:
from django.db import models
from django.core.validators import RegexValidator
# Create your models here.
class Customer(models.Model):
customer_id = models.AutoField(primary_key=True,unique=True)
full_name = models.CharField(max_length=50)
user_email = models.EmailField(max_length=50)
user_pass = models.CharField(max_length=30)
def __str__(self):
return "%s" % self.full_name
class CustomerDetail(models.Model):
phone_regex = RegexValidator(regex = r'^\d{10}$', message = "Invalid format! E.g. 4088385778")
date_regex = RegexValidator(regex = r'\d{2}[-/]\d{2}[-/]\d{2}', message = "Invalid format! E.g. 05/16/91")
address = models.CharField(max_length=100)
date_of_birth = models.CharField(validators = [date_regex], max_length = 10, blank = True)
company = models.CharField(max_length=30)
home_phone = models.CharField(validators = [phone_regex], max_length = 10, blank = True)
work_phone = models.CharField(validators = [phone_regex], max_length = 10, blank = True)
customer_id = models.ForeignKey(Customer, on_delete=models.CASCADE)
I added customer_id to Customer after I added the same in CustomerDetail as foreign key. Why do I still get this error after running migrate, even after I added unique=True to customer_id?
Error:
Rendering model states... DONE
Applying newuser.0003_auto_20160823_0128...Traceback (most recent call last):
File "/home/krag91/Documents/djangodev/virtualenv /lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
File "/home/krag91/Documents/djangodev/virtualenv /lib/python3.5/site-packages/django/db/backends/sqlite3/base.py", line 337, in execute
return Database.Cursor.execute(self, query, params)
sqlite3.IntegrityError: UNIQUE constraint failed: newuser_customer.customer_id
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "manage.py", line 22, in <module>
execute_from_command_line(sys.argv)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/core/management/__init__.py", line 367, in execute_from_command_line utility.execute()
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/core/management/__init__.py", line 359, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/core/management/base.py", line 305, in run_from_argv
self.execute(*args, **cmd_options)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/core/management/base.py", line 356, in execute
output = self.handle(*args, **options)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/core/management/commands/migrate.py", line 202, in handle
targets, plan, fake=fake, fake_initial=fake_initial
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/migrations/executor.py", line 97, in migrate
state = self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/migrations/executor.py", line 132, in _migrate_all_forwards
state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/migrations/executor.py", line 237, in apply_migration
state = migration.apply(state, schema_editor)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/migrations/migration.py", line 129, in apply
operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/migrations/operations/fields.py", line 84, in database_forwards
field,
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/backends/sqlite3/schema.py", line 231, in add_field
self._remake_table(model, create_fields=[field])
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/backends/sqlite3/schema.py", line 199, in _remake_table
self.quote_name(model._meta.db_table),
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/backends/base/schema.py", line 112, in execute
cursor.execute(sql, params)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/backends/utils.py", line 79, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/utils.py", line 94, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/utils/six.py", line 685, in reraise
raise value.with_traceback(tb)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
File "/home/krag91/Documents/djangodev/virtualenv/lib/python3.5/site-packages/django/db/backends/sqlite3/base.py", line 337, in execute
return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: UNIQUE constraint failed: newuser_customer.customer_id

Answer 1

It seems like you are already having some objects as per old model definitions. By default django creates a field named as id to every model in database. It can be accesses by modelName.id.
In your case I guess what happened is that you are having some objects in database with customer.id as primary as primary key. So when you changed the models and applied migrations, existing objects are checked and another unique field is tried to added as a primary key. Here the workaround is to delete all the existing objects after removing the customer_id field and then try recreating the field and run migrations.
HTH