Method lazy_model_operation

django/apps/registry.py:388–426

Take a function and a number of ("app_label", "modelname") tuples, and when all the corresponding models have been imported and registered, call the function with the model classes as its arguments. The function passed to this method must accept exactly n models as

(self, function, *model_keys)

                    model._meta._expire_cache()

    def lazy_model_operation(self, function, *model_keys):
        """
        Take a function and a number of ("app_label", "modelname") tuples, and
        when all the corresponding models have been imported and registered,
        call the function with the model classes as its arguments.

        The function passed to this method must accept exactly n models as
        arguments, where n=len(model_keys).
        """
        # Base case: no arguments, just execute the function.
        if not model_keys:
            function()
        # Recursive case: take the head of model_keys, wait for the
        # corresponding model class to be imported and registered, then apply
        # that argument to the supplied function. Pass the resulting partial
        # to lazy_model_operation() along with the remaining model args and
        # repeat until all models are loaded and all arguments are applied.
        else:
            next_model, *more_models = model_keys

            # This will be executed after the class corresponding to next_model
            # has been imported and registered. The `func` attribute provides
            # duck-type compatibility with partials.
            def apply_next_model(model):
                next_function = partial(apply_next_model.func, model)
                self.lazy_model_operation(next_function, *more_models)

            apply_next_model.func = function

            # If the model has already been imported and registered, partially
            # apply it to the function now. If not, add it to the list of
            # pending operations for the model, where it will be executed with
            # the model class as its sole argument once the model is ready.
            try:
                model_class = self.get_registered_model(*next_model)
            except LookupError:
                self._pending_operations[next_model].append(apply_next_model)
            else:
                apply_next_model(model_class)

    def do_pending_operations(self, model):
        """