def METHOD_NAME(self, group=None):
    """Creates the relation for the class:`Link`.
    Parameters
    ----------
    group : list
        List of oemof.solph.components.Link objects for which
        the relation of inputs and outputs is createdBuildAction
        e.g. group = [link1, link2, link3, ...]. The components inside
        the list need to hold an attribute `conversion_factors` of type
        dict containing the conversion factors for all inputs to outputs.
    """
    if group is None:
        return None
    m = self.parent_block()
    all_conversions = {}
    for n in group:
        all_conversions[n] = {
            k: v for k, v in n.conversion_factors.items()
        }
    self.LINKS = Set(initialize=[g for g in group])
    def _input_output_relation(block):
        for p, t in m.TIMEINDEX:
            for n, conversion in all_conversions.items():
                for cidx, c in conversion.items():
                    try:
                        expr = (
                            m.flow[n, cidx[1], p, t]
                            == c[t] * m.flow[cidx[0], n, p, t]
                        )
                    except KeyError:
                        raise KeyError(
                            "Error in constraint creation "
                            f"from: {cidx[0]}, to: {cidx[1]}, via: {n}. "
                            "Check if all connected buses match "
                            "the conversion factors.",
                        )
                    block.relation.add((n, cidx[0], cidx[1], p, t), expr)
    self.relation = Constraint(
        [
            (n, cidx[0], cidx[1], p, t)
            for p, t in m.TIMEINDEX
            for n, conversion in all_conversions.items()
            for cidx, c in conversion.items()
        ],
        noruleinit=True,
    )
    self.relation_build = BuildAction(rule=_input_output_relation)