A hacky script to rewrite old Django migrations to include current on_delete values

fix_migrations.py

#!/usr/bin/env python

# IMPORTANT! USAGE INSTRUCTIONS!
# Drop this file in the top level of your project *after* you've added on_delete to all your ForeignKey and
# OneToOneFields. Running it will rewrite your migration files to add whatever the current on_delete for each field is
# to the past migrations. Make sure you have a clean working copy so you can easily review the differences before
# committing. Assuming there were no pending migrations, running "makemigrations" should yield no new changes.


import os
import re

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "project.settings")

import django
django.setup()

from django.apps import apps
from django.db import models


MIGRATION_TYPE_RE = re.compile(r'\s*migrations.([^(]+)\(')
MODEL_NAME_RE = re.compile(r"\s*model_name='([^']+)',")
NAME_RE = re.compile(r"\s*name='([^']+)',")
FK_NAME_RE = re.compile(r"\s*\('([^']+)', models\.(ForeignKey|OneToOneField)")
FIELD_TYPE_RE = re.compile(r"models\.(ForeignKey|OneToOneField)\(")


top_level = os.path.dirname(os.path.abspath(__file__))
current_on_delete = {}


# Go through all the fields and figure out what the current on_delete values are.
for model_class in apps.get_models():
    for field in model_class._meta.fields:
        if isinstance(field, (models.ForeignKey, models.OneToOneField)):
            current_on_delete['%s.%s' % (model_class.__name__.lower(), field.name)] = field.remote_field.on_delete.__name__


for app_config in apps.get_app_configs():
    if app_config.path.startswith(top_level):
        migrations_path = os.path.join(app_config.path, 'migrations')
        if os.path.isdir(migrations_path):
            for filename in os.listdir(migrations_path):
                if filename.endswith('.py'):
                    file_path = os.path.join(migrations_path, filename)
                    file_lines = []
                    print(file_path)
                    # Keep track of the last known migration type, model_name, and name attributes.
                    migration_type = None
                    model_name = None
                    name = None
                    for lineno, line in enumerate(open(file_path)):
                        match = FIELD_TYPE_RE.search(line)
                        if match and 'on_delete' not in line:
                            field_type = match.group(1)
                            match = FK_NAME_RE.match(line)
                            if match:
                                # For CreateModel, each FK is on it's own line, prefixed by the field name - use the last known "name" as the model name.
                                key = '%s.%s' % (name.lower(), match.group(1))
                            else:
                                # Otherwise, use the last name/model_name attributes to look up the FK.
                                key = '%s.%s' % (model_name, name)
                            new_line = line.replace('models.%s(' % field_type, 'models.%s(on_delete=models.%s, ' % (field_type, current_on_delete[key]))
                            print('  %s: %s\n    %s\n    %s' % (lineno + 1, key, line.strip(), new_line.strip()))
                            # TODO: add dry-run flag instead of always replacing
                            line = new_line
                        else:
                            match = MIGRATION_TYPE_RE.match(line)
                            if match:
                                migration_type = match.group(1)
                            match = MODEL_NAME_RE.match(line)
                            if match:
                                model_name = match.group(1)
                            match = NAME_RE.match(line)
                            if match:
                                name = match.group(1)
                        file_lines.append(line)
                    # Write out the new file with any fixed lines.
                    new_contents = ''.join(file_lines)
                    with open(file_path, 'w') as f:
                        f.write(new_contents)