如何从Django删除模型？

Question

I want to delete some tables from database. Earlier, I had models like course, department. Now, I want to delete all of them from database and use only one:

class Student(models.Model):
    """here goes model for users"""

    def __str__(self):
        return self.name

    name = models.CharField(default = "",max_length=200)
    enrollment_no = models.CharField(default = "",max_length=10)
    batch = models.CharField(default = "",max_length=4)
    father_income = models.IntegerField(max_length=100)
    email = models.CharField(default = "",max_length=1000)
    mobile_number = models.CharField(default = "",max_length=1000)

But, when I am using:

python manage.py makemigrations

It says no changes detected. And on running command:

python manage.py migrate

I am getting all my tables back in the database, while those table doesn't exist in models.py. I tried to use:

  382  python manage.py makemigrations
  383  python manage.py squashmigrations
  384  python manage.py squashmigrations appname
  385  python manage.py squashmigrations appname 001
  386  python manage.py squashmigrations appname 0001
  387  python manage.py makemigrations 
  388  python manage.py migrate
  389  python manage.py Reporter.objects.all().delete()
  390  Reporter.objects.all().delete()
  391  python manage.py sqlclear appname | python manage.py dbshell
  392  python manage.py sqlclear appname
  393  ./manage.py sqlclear appname | ./manage.py dbshell
  394  python manage.py sqlclear
  395  python manage.py flush
  396  python manage.py syncdb
  397  python manage.py makemigrations
  398  python manage.py migrate
  399  python manage.py makemigrations
  400  python manage.py migrate
  401  python manage.py makemigrations
  402  python manage.py flush
  403  python manage.py makemigrations
  404  python manage.py migrate
  405  python manage.py makemigrations
  406  python manage.py migrate
  407  python manage.py makemigrations
  408  python manage.py migrate
  409  python manage.py sqlflush
  410  python manage.py sqlflush | python manage.py dbshell
  411  python manage.py sqlclear jmialumniusa_app
  412  python manage.py help flush
  413  python manage.py flush
  414  python manage.py makemigrations
  415  python manage.py migrate
  416  python manage.py schemamigration --auto appname/
  417  python manage.py schemamigration --auto appname
  418  python manage.py makemigrations
  419  history

but getting no success. Please help me to solve this.

The output of python manage.py makemigrations jmialumniusa_app is:

System check identified some issues:

WARNINGS:
?: (urls.W001) Your URL pattern '^$' uses include with a regex ending with a '$'. Remove the dollar from the regex to avoid problems including URLs.
No changes detected in app 'jmialumniusa_app'

And finally on python manage.py migrate I am getting:

System check identified some issues:

WARNINGS:
?: (urls.W001) Your URL pattern '^$' uses include with a regex ending with a '$'. Remove the dollar from the regex to avoid problems including URLs.
Operations to perform:
  Apply all migrations: admin, contenttypes, sessions, auth, jmialumniusa_app
Running migrations:
  Rendering model states... DONE
  Applying jmialumniusa_app.0003_auto_20160506_0654...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 345, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 348, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 399, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/migrate.py", line 200, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 92, in migrate
    self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 121, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 198, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/migration.py", line 123, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/operations/fields.py", line 121, in database_forwards
    schema_editor.remove_field(from_model, from_model._meta.get_field(self.name))
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/schema.py", line 438, in remove_field
    self.execute(sql)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/schema.py", line 110, in execute
    cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 79, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 95, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/base.py", line 112, in execute
    return self.cursor.execute(query, args)
  File "/usr/lib/python2.7/dist-packages/MySQLdb/cursors.py", line 174, in execute
    self.errorhandler(self, exc, value)
  File "/usr/lib/python2.7/dist-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
django.db.utils.OperationalError: (1091, "Can't DROP 'student_id'; check that column/key exists")

Answer 1

after deleting your unwanted models from models.py, try this:

python manage.py makemigrations your_app
python manage.py migrate

reason can be that your app might not have been yet "registered" to have migrations

Answer 2

The first answer should work for you. Another thing you can do is delete the migrations folder in the app and run python manage.py makemigrations app_name

A new migrations folder will be automatically created. then you can migrate

python manage.py migrate You should be good after this. I DO NOT ENCOURAGE THIS but as a last resort, if you are using sqlite, just delete it and do the what I stated above.

https://docs.djangoproject.com/en/1.9/topics/migrations/ will give you more insights on how migrations work in django.

Answer 3

When I had same issue, I fixed it by this way:

• open your app folder, then open migrations folder
• delete all files except init
• try makemigrations and migrate again

It may not help if the problem is in DB, not in migrations.