Set the value of the refernce field

def set(self, instance, value, **kw):  # noqa
        """Set the value of the refernce field
        """
        ref = []

        # The value is an UID
        if api.is_uid(value):
            ref.append(api.get_object_by_uid(value))

        # The value is already an object
        if api.is_at_content(value):
            ref.append(value)

        # The value is a dictionary
        # -> handle it like a catalog query
        if u.is_dict(value):
            results = api.search(portal_type=self.allowed_types, **value)
            ref = map(api.get_object, results)

        # The value is a list
        if u.is_list(value):
            for item in value:
                # uid
                if api.is_uid(item):
                    ref.append(api.get_object_by_uid(item))
                    continue

                # object
                if api.is_at_content(item):
                    ref.append(api.get_object(item))
                    continue

                # path
                if api.is_path(item):
                    ref.append(api.get_object_by_path(item))
                    continue

                # dict (catalog query)
                if u.is_dict(item):
                    # If there is UID of objects, just use it.
                    uid = item.get('uid', None)
                    if uid:
                        obj = api.get_object_by_uid(uid)
                        ref.append(obj)
                    else:
                        results = api.search(portal_type=self.allowed_types, **item)
                        objs = map(api.get_object, results)
                        ref.extend(objs)
                    continue

                # Plain string
                # -> do a catalog query for title
                if isinstance(item, basestring):
                    results = api.search(portal_type=self.allowed_types, title=item)
                    objs = map(api.get_object, results)
                    ref.extend(objs)
                    continue

        # The value is a physical path
        if api.is_path(value):
            ref.append(api.get_object_by_path(value))

        # Handle non multi valued fields
        if not self.multi_valued:
            if len(ref) > 1:
                raise ValueError("Multiple values given for single valued "
                                 "field {}".format(repr(self.field)))
            else:
                ref = ref[0]
        return self._set(instance, ref, **kw)