Default queryset method call manager

managers.py

from collections import deque

from django.db import models


class MethodCalls(object):
    """
    A mock object which logs chained method calls.
    """
    def __init__(self):
        self._calls = deque()

    def __getattr__(self, name):
        c = Call(self, name)
        self._calls.append(c)
        return c

    def __iter__(self):
        for c in self._calls:
            yield tuple(c)


class Call(object):
    """
    Used by `MethodCalls` objects internally to represent chained method calls.
    """
    def __init__(self, calls_obj, method_name):
        self._calls = calls_obj
        self.method_name = method_name

    def __call__(self, *method_args, **method_kwargs):
        self.method_args = method_args
        self.method_kwargs = method_kwargs

        return self._calls

    def __iter__(self):
        yield self.method_name
        yield self.method_args
        yield self.method_kwargs


class DefaultQuerysetMethodCallsManager(models.Manager):
    """
    A model manager class which allows specification of a sequence of
    method calls to be applied by default to base querysets.
    `DefaultQuerysetMethodCallsManager` instances expose a property
    `default_queryset_method_calls` to which chained method calls can be
    applied to indicate which methods should be called on base querysets.

    For example::

        class Sandwich(models.Model):
            bread = models.ForeignKey(Bread)
            extras = models.ManyToManyField(Extra)

            # Other field definitions...

            objects = DefaultQuerysetMethodCallsManager()
            objects.default_queryset_method_calls.filter(
                bread__type='wheat',
            ).select_related(
                'bread',
            ).prefetch_related(
                'extras',
            )
    """
    def __init__(self, *args, **kwargs):
        self.default_queryset_method_calls = MethodCalls()

        super(DefaultQuerysetMethodCallsManager, self).__init__(*args, **kwargs)

    def get_query_set(self, *args, **kwargs):
        qs = super(DefaultQuerysetMethodCallsManager, self).get_query_set(*args, **kwargs)

        for method_name, method_args, method_kwargs in self.default_queryset_method_calls:
            qs = getattr(qs, method_name)(*method_args, **method_kwargs)

        return qs