id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
24182	Bug with functional default and migrations	arveitch	nobody	"I've found a bug on all of 1.7; I've tested up to 1.7.3. The code works fine on 1.6. I think this is a reasonably common design pattern.

Here's the models.py:
{{{
import random
from django.db import models

def generateCode(prefix=''):
    while True:
        code = ''.join(
            # Omit I, O, 1 and 0 as they can cause confusion
           random.choice('ABCDEFGHJKLMNPQRSTUVWXYZ23456789')
           for i in range(7)
        )
        code = prefix + code
        if not PromotionalCode.objects.filter(code=code).exists():
            break
    return code


class PromotionalCode(models.Model):
    code = models.CharField(
        default=generateCode, db_index=True, max_length=12, unique=True
    )
    value_amount = models.DecimalField(
        default=0, max_digits=7, decimal_places=2
    )
}}}

./manage.py migrate gives this traceback:

{{{
  Applying example.0001_initial...Traceback (most recent call last):
  File ""./manage.py"", line 10, in <module>
    execute_from_command_line(sys.argv)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py"", line 385, in execute_from_command_line
    utility.execute()
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py"", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py"", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py"", line 338, in execute
    output = self.handle(*args, **options)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/commands/migrate.py"", line 161, in handle
    executor.migrate(targets, plan, fake=options.get(""fake"", False))
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/migrations/executor.py"", line 68, in migrate
    self.apply_migration(migration, fake=fake)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/migrations/executor.py"", line 102, in apply_migration
    migration.apply(project_state, schema_editor)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/migrations/migration.py"", line 108, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/migrations/operations/models.py"", line 36, in database_forwards
    schema_editor.create_model(model)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/schema.py"", line 213, in create_model
    definition, extra_params = self.column_sql(model, field)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/schema.py"", line 125, in column_sql
    default_value = self.effective_default(field)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/schema.py"", line 175, in effective_default
    default = field.get_default()
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/fields/__init__.py"", line 719, in get_default
    return self.default()
  File ""/Users/andrew/Sites/testing/example/models.py"", line 12, in generateCode
    if not PromotionalCode.objects.filter(code=code).exists():
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/query.py"", line 606, in exists
    return self.query.has_results(using=self.db)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/sql/query.py"", line 457, in has_results
    return compiler.has_results()
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/sql/compiler.py"", line 757, in has_results
    return bool(self.execute_sql(SINGLE))
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/sql/compiler.py"", line 786, in execute_sql
    cursor.execute(sql, params)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/utils.py"", line 81, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/utils.py"", line 65, in execute
    return self.cursor.execute(sql, params)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/utils.py"", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/utils.py"", line 65, in execute
    return self.cursor.execute(sql, params)
  File ""/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/sqlite3/base.py"", line 485, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.OperationalError: no such table: example_promotionalcode
}}}"	Bug	new	Migrations	1.7	Normal				Unreviewed	0	0	0	0	0	0