I want to remove an app from a django project.

I want to remove

the tables of the app
the content-types
foreign-key usages of these content-types

Running manage.py migrate app_to_remove zero does not work:

django.db.migrations.migration.IrreversibleError: 
Operation <RunPython <function forwards_func at 0x7ff76075d668>> in
            fooapp.0007_add_bar is not reversible

I guess there are several migrations which are not reversible ...

First: Remove references in the code

remove app_to_remove from settings.INSTALLED_APPS
remove other references in urls.py or other places

Second: Clean the database

Create an empty migration for your django-project:

manage.py makemigrations your_django_project --empty

Edit the file. Here is a template:

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('your_django_project', '0001_initial'),
    ]

    operations = [
        migrations.RunSQL('''
        drop if exists table app_to_remove_table1;
        drop if exists table app_to_remove_table2;
        ....
        delete from auth_permission where content_type_id in (select id from django_content_type where app_label = '{app_label}');
        delete from django_admin_log where content_type_id in (select id from django_content_type where app_label = '{app_label}');
        delete from reversion_version where content_type_id in (select id from django_content_type where app_label = '{app_label}');
        delete from django_content_type where app_label = '{app_label}';
        delete from django_migrations where app='{app_label}';
        '''.format(app_label='app_to_remove'))
    ]

Run the migration, run tests.

About "drop if exists": You have two cases: