Method _load_via_parent

lib/sqlalchemy/orm/strategies.py:3465–3515

(
        self, our_states, query_info, q, context, execution_options, chunksize
    )

            state.get_impl(self.key).set_committed_value(state, dict_, None)

    def _load_via_parent(
        self, our_states, query_info, q, context, execution_options, chunksize
    ):
        uselist = self.uselist
        n_pk = query_info.n_pk
        _empty_result = () if uselist else None

        while our_states:
            chunk = our_states[0:chunksize]
            our_states = our_states[chunksize:]

            primary_keys = [
                key[0] if query_info.zero_idx else key
                for key, state, state_dict, overwrite in chunk
            ]

            result = context.session.execute(
                q,
                params={"primary_keys": primary_keys},
                execution_options=execution_options,
            )
            if result.context is not None and result.context.requires_uniquing:
                rows = result.unique()
            else:
                rows = result._raw_all_tuples()
            data = collections.defaultdict(list)
            for row in rows:
                data[row[:n_pk]].append(row[n_pk])

            for key, state, state_dict, overwrite in chunk:
                if not overwrite and self.key in state_dict:
                    continue

                collection = data.get(key, _empty_result)

                if not uselist and collection:
                    if len(collection) > 1:
                        util.warn(
                            "Multiple rows returned with "
                            "uselist=False for eagerly-loaded "
                            "attribute '%s' " % self
                        )
                    state.get_impl(self.key).set_committed_value(
                        state, state_dict, collection[0]
                    )
                else:
                    # note that empty tuple set on uselist=False sets the
                    # value to None
                    state.get_impl(self.key).set_committed_value(
                        state, state_dict, collection
                    )


def _single_parent_validator(desc, prop):