from importlib import import_module from django.utils.version import get_docs_version def deconstructible(*args, path=None): """ Class decorator that allows the decorated class to be serialized by the migrations subsystem. The `path` kwarg specifies the import path. """ def decorator(klass): def __new__(cls, *args, **kwargs): # We capture the arguments to make returning them trivial obj = super(klass, cls).__new__(cls) obj._constructor_args = (args, kwargs) return obj def deconstruct(obj): """ Return a 3-tuple of class import path, positional arguments, and keyword arguments. """ # Fallback version if path: module_name, _, name = path.rpartition('.') else: module_name = obj.__module__ name = obj.__class__.__name__ # Make sure it's actually there and not an inner class module = import_module(module_name) if not hasattr(module, name): raise ValueError( "Could not find object %s in %s.\n" "Please note that you cannot serialize things like inner " "classes. Please move the object into the main module " "body to use migrations.\n" "For more information, see " "https://docs.djangoproject.com/en/%s/topics/migrations/#serializing-values" % (name, module_name, get_docs_version())) return ( path or '%s.%s' % (obj.__class__.__module__, name), obj._constructor_args[0], obj._constructor_args[1], ) klass.__new__ = staticmethod(__new__) klass.deconstruct = deconstruct return klass if not args: return decorator return decorator(*args)