code: function(criteria, cb) {
          if (_.isFunction(criteria)) { cb = criteria; criteria = undefined; }
          this.findBy(criteria, function(err, entities) {
            if (err) { return cb(err); }
            var deleteEntity = function(entity, callback) {
              entity.delete(callback);
            };
            async.each(entities, deleteEntity, function(err) {
              cb(err);
            });
          });
        }
docs: destroys (retrieve and delete) all entities matching criteria (criteria is optional)