Lock PostgreSQL table in Django app

transaction.py

from django.db.transaction import *  # NOQA
from django.utils.decorators import ContextDecorator

LOCK_MODES = (
    'ACCESS SHARE',
    'ROW SHARE',
    'ROW EXCLUSIVE',
    'SHARE UPDATE EXCLUSIVE',
    'SHARE',
    'SHARE ROW EXCLUSIVE',
    'EXCLUSIVE',
    'ACCESS EXCLUSIVE',
)

class require_lock(ContextDecorator):
    """
    Decorator for PostgreSQL's table-level lock functionality
    
    example:
        @transaction.commit_on_success
        @require_lock(MyModel, 'ACCESS EXCLUSIVE')
        def myview(request)
            ...
    
    example:
        # Uses exclusive lock instead of unique index to create unique instance of a model.
        def get_or_create(**kwargs):
            with transaction.require_lock(MyModel, 'ACCESS EXCLUSIVE'):
                return MyModel.objects.get_or_create(**kwargs)
    
    see:
        Original source code:
            https://www.caktusgroup.com/blog/2009/05/26/explicit-table-locking-with-postgresql-and-django/
        PostgreSQL's LOCK Documentation:
            https://www.postgresql.org/docs/9.4/static/explicit-locking.html
    """
    def __init__(self, model, lock):
        self.db_table = model._meta.db_table
        self.lock = lock

        if lock not in LOCK_MODES:
            raise ValueError('%s is not a PostgreSQL supported lock mode.')

    def __enter__(self):
        from django.db import connection
        cursor = connection.cursor()
        cursor.execute('LOCK TABLE %s IN %s MODE' % (self.db_table, self.lock))

    def __exit__(self, exc_type, exc_value, traceback):
        pass