Rewrite manually optimized squash migrations.

optimizemigration.py

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from django.core.management import BaseCommand
from django.db import DEFAULT_DB_ALIAS, migrations
from django.db import connections
from django.db.migrations.loader import MigrationLoader
from django.db.migrations.optimizer import MigrationOptimizer
from django.db.migrations.writer import MigrationWriter


class Command(BaseCommand):
    help = "Optimize a single migration. Useful for re-optimizing squashed migrations have been manually edited to " \
           "move safe RunSQL or RunPython commands to the end (or to a separate migration)."

    def add_arguments(self, parser):
        parser.add_argument('app_label', help='App label of the application containing the migration to optimize.')
        parser.add_argument('migration_name', help='Name of the migration to optimize.')

    def handle(self, **options):
        verbosity = options['verbosity']
        app_label = options['app_label']
        migration_name = options['migration_name']

        loader = MigrationLoader(connections[DEFAULT_DB_ALIAS])
        migration = loader.get_migration(app_label, migration_name)
        optimizer = MigrationOptimizer()
        new_operations = optimizer.optimize(migration.operations, migration.app_label)
        if migration.operations == new_operations:
            if verbosity > 0:
                self.stdout.write(self.style.MIGRATE_HEADING("Nothing to do. Migration is already optimized."))
            return
        subclass = type(str("Migration"), (migrations.Migration, ), {
            "dependencies": migration.dependencies,
            "operations": new_operations,
            "replaces": migration.replaces,
        })
        new_migration = subclass("%s_optimized" % migration.name, app_label)

        # Write out the new migration file
        writer = MigrationWriter(new_migration)
        with open(writer.path, "w") as fh:
            fh.write(writer.as_string())

        if verbosity > 0:
            self.stdout.write(self.style.MIGRATE_HEADING("Created new optimized migration %s" % writer.path))
            self.stdout.write("  You should diff this migration to check the optimizations.")
            if not writer.needs_manual_porting:
                self.stdout.write("  If satisfied with the optimizations, you can move the new migration")
                self.stdout.write("  over the old migration.")
            else:
                self.stdout.write(self.style.MIGRATE_HEADING("Manual porting required"))
                self.stdout.write("  Your migrations contained functions that we could not safely copy")
                self.stdout.write("  their implementation.")
                self.stdout.write("  If satisfied with the optimizations, you should move the operations to the old")
                self.stdout.write("  file and delete the new migration.")