from django.contrib.contenttypes.models import ContentType

def fetch_content_objects(tagged_items, select_related_for=None):

    """

    Retrieves ``ContentType`` and content objects for the given list of

    ``TaggedItems``, grouping the retrieval of content objects by model

    type to reduce the number of queries executed.

    This results in ``number_of_content_types + 1`` queries rather than

    the ``number_of_tagged_items * 2`` queries you'd get by iterating

    over the list and accessing each item's ``object`` attribute.

    A ``select_related_for`` argument can be used to specify a list of

    of model names (corresponding to the ``model`` field of a

    ``ContentType``) for which ``select_related`` should be used when

    retrieving model instances.

    """

    if select_related_for is None: select_related_for = []

    # Group content object pks by their content type pks

    objects = {}

    for item in tagged_items:

        objects.setdefault(item.content_type_id, []).append(item.object_id)

    # Retrieve content types and content objects in bulk

    content_types = ContentType._default_manager.in_bulk(objects.keys())

    for content_type_pk, object_pks in objects.iteritems():

        model = content_types[content_type_pk].model_class()

        if content_types[content_type_pk].model in select_related_for:

            objects[content_type_pk] = model._default_manager.select_related().in_bulk(object_pks)

        else:

            objects[content_type_pk] = model._default_manager.in_bulk(object_pks)

    # Set content types and content objects in the appropriate cache

    # attributes, so accessing the 'content_type' and 'object'

    # attributes on each tagged item won't result in further database

    # hits.

    for item in tagged_items:

        item._object_cache = objects[item.content_type_id][item.object_id]

        item._content_type_cache = content_types[item.content_type_id]