How to fix South Python migrations error?

Question

Django

Adding a new field to the model

class Technics(models.Model):
    tech_model = models.CharField(max_length=200)
    tech_description = models.CharField(max_length=1500)
    category_tech = models.ForeignKey(TechCategory)
    pub_date = models.DateTimeField('date published')
    brand = models.ForeignKey(Manufacturer)
    currency = models.ForeignKey(Currency)
    price = models.IntegerField(default=0)
    created_by = models.IntegerField(default=0)
    active = models.BooleanField()
    pr_image = models.ImageField(upload_to="preview", null=True, blank=True) #new field
    def __unicode__(self):
        return "%s - %s - %s - %s - %s - %s - %s - %s" % (self.tech_model, self.pr_image, self.tech_description, self.pub_date >= timezone.now() - datetime.timedelta(days=1), self.brand, self.currency, self.price, self.created_by, self.active)

I run manage.py schemamigration --auto - everything goes well at this stage
Then I run manage.py migration and I get the following output:

Running migrations for technics:
 - Migrating forwards to 0008_auto__chg_field_technics_pr_image.
 > technics:0006_auto__del_field_technics_pr_image
FATAL ERROR - The following SQL query failed: ALTER TABLE `technics_technics` DROP COLUMN `pr_image` CASCADE;
The error was: (1091, "Can't DROP 'pr_image'; check that column/key exists")
 ! Error found during real run of migration! Aborting.

 ! Since you have a database that does not support running
 ! schema-altering statements in transactions, we have had 
 ! to leave it in an interim state between migrations.

! You *might* be able to recover with:   = ALTER TABLE `technics_technics` ADD COLUMN `pr_image` varchar(100) NOT NULL DEFAULT '0'; []
   - no dry run output for alter_column() due to dynamic DDL, sorry

 ! The South developers regret this has happened, and would
 ! like to gently persuade you to consider a slightly
 ! easier-to-deal-with DBMS (one that supports DDL transactions)
 ! NOTE: The error which caused the migration to fail is further up.
Error in migration: technics:0006_auto__del_field_technics_pr_image
Traceback (most recent call last):
  File "/Users/elchinmirzayev/Documents/Aptana Studio 3 Workspace/dj_stroyka_165/manage.py", line 11, in <module>
    execute_from_command_line(sys.argv)
  File "/Library/Python/2.7/site-packages/django/core/management/__init__.py", line 399, in execute_from_command_line
    utility.execute()
  File "/Library/Python/2.7/site-packages/django/core/management/__init__.py", line 392, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 242, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 285, in execute
    output = self.handle(*args, **options)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/management/commands/migrate.py", line 111, in handle
    ignore_ghosts = ignore_ghosts,
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/migration/__init__.py", line 220, in migrate_app
    success = migrator.migrate_many(target, workplan, database)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/migration/migrators.py", line 256, in migrate_many
    result = migrator.__class__.migrate_many(migrator, target, migrations, database)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/migration/migrators.py", line 331, in migrate_many
    result = self.migrate(migration, database)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/migration/migrators.py", line 133, in migrate
    result = self.run(migration, database)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/migration/migrators.py", line 114, in run
    return self.run_migration(migration, database)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/migration/migrators.py", line 84, in run_migration
    migration_function()
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/migration/migrators.py", line 60, in <lambda>
    return (lambda: direction(orm))
  File "/Users/elchinmirzayev/Documents/Aptana Studio 3 Workspace/dj_stroyka_165/technics/migrations/0006_auto__del_field_technics_pr_image.py", line 12, in forwards
    db.delete_column(u'technics_technics', 'pr_image')
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/db/mysql.py", line 28, in _column_rm
    return func(self, table_name, column_name, *args, **opts)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/db/mysql.py", line 227, in delete_column
    super(DatabaseOperations, self).delete_column(table_name, name)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/db/generic.py", line 54, in _column_rm
    return func(self, table, column, *args, **opts)
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/db/generic.py", line 911, in delete_column
    self.execute(self.delete_column_string % params, [])
  File "/Library/Python/2.7/site-packages/South-1.0-py2.7.egg/south/db/generic.py", line 282, in execute
    cursor.execute(sql, params)
  File "/Library/Python/2.7/site-packages/django/db/backends/util.py", line 69, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/Library/Python/2.7/site-packages/django/db/backends/util.py", line 53, in execute
    return self.cursor.execute(sql, params)
  File "/Library/Python/2.7/site-packages/django/db/utils.py", line 99, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/Library/Python/2.7/site-packages/django/db/backends/util.py", line 53, in execute
    return self.cursor.execute(sql, params)
  File "/Library/Python/2.7/site-packages/django/db/backends/mysql/base.py", line 124, in execute
    return self.cursor.execute(query, args)
  File "/Library/Python/2.7/site-packages/MySQLdb/cursors.py", line 201, in execute
    self.errorhandler(self, exc, value)
  File "/Library/Python/2.7/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
django.db.utils.OperationalError: (1091, "Can't DROP 'pr_image'; check that column/key exists")
Finished "/Users/elchinmirzayev/Documents/Aptana Studio 3 Workspace/dj_stroyka_165/manage.py migrate technics" execution.

I looked through all the South documentation, but did not find anything sensible about this.
How to implement migration?

Answer 1

judging by the name of the migration, you are deleting this field, not adding it - del_field_technics_pr_image