Class RelationshipCache

examples/dogpile_caching/caching_query.py:156–214

Specifies that a Query as called within a "lazy load" should load results from a cache.

class RelationshipCache(FromCache):
    """Specifies that a Query as called within a "lazy load"
    should load results from a cache."""

    propagate_to_loaders = True

    def __init__(
        self,
        attribute,
        region="default",
        cache_key=None,
        expiration_time=None,
        ignore_expiration=False,
    ):
        """Construct a new RelationshipCache.

        :param attribute: A Class.attribute which
         indicates a particular class relationship() whose
         lazy loader should be pulled from the cache.

        :param region: name of the cache region.

        :param cache_key: optional.  A string cache key
         that will serve as the key to the query, bypassing
         the usual means of forming a key from the Query itself.

        """
        self.region = region
        self.cache_key = cache_key
        self.expiration_time = expiration_time
        self.ignore_expiration = ignore_expiration
        self._relationship_options = {
            (attribute.property.parent.class_, attribute.property.key): self
        }

    def _process_orm_context(self, orm_context):
        current_path = orm_context.loader_strategy_path

        if current_path:
            mapper, prop = current_path[-2:]
            key = prop.key

            for cls in mapper.class_.__mro__:
                if (cls, key) in self._relationship_options:
                    relationship_option = self._relationship_options[
                        (cls, key)
                    ]
                    return relationship_option

    def and_(self, option):
        """Chain another RelationshipCache option to this one.

        While many RelationshipCache objects can be specified on a single
        Query separately, chaining them together allows for a more efficient
        lookup during load.

        """
        self._relationship_options.update(option._relationship_options)