Function _relationships_for_fks

lib/sqlalchemy/ext/automap.py:1492–1599

(
    automap_base: Type[Any],
    map_config: _DeferredDeclarativeConfig,
    table_to_map_config: Union[
        Dict[Optional[Table], _DeferredDeclarativeConfig],
        Dict[Table, _DeferredDeclarativeConfig],
    ],
    collection_class: type,
    name_for_scalar_relationship: NameForScalarRelationshipType,
    name_for_collection_relationship: NameForCollectionRelationshipType,
    generate_relationship: GenerateRelationshipType,
)

def _relationships_for_fks(
    automap_base: Type[Any],
    map_config: _DeferredDeclarativeConfig,
    table_to_map_config: Union[
        Dict[Optional[Table], _DeferredDeclarativeConfig],
        Dict[Table, _DeferredDeclarativeConfig],
    ],
    collection_class: type,
    name_for_scalar_relationship: NameForScalarRelationshipType,
    name_for_collection_relationship: NameForCollectionRelationshipType,
    generate_relationship: GenerateRelationshipType,
) -> None:
    local_table = cast("Optional[Table]", map_config.local_table)
    local_cls = cast(
        "Optional[Type[Any]]", map_config.cls
    )  # derived from a weakref, may be None

    if local_table is None or local_cls is None:
        return
    for constraint in local_table.constraints:
        if isinstance(constraint, ForeignKeyConstraint):
            fks = constraint.elements
            referred_table = fks[0].column.table
            referred_cfg = table_to_map_config.get(referred_table, None)
            if referred_cfg is None:
                continue
            referred_cls = referred_cfg.cls

            if local_cls is not referred_cls and issubclass(
                local_cls, referred_cls
            ):
                continue

            relationship_name = name_for_scalar_relationship(
                automap_base, local_cls, referred_cls, constraint
            )
            backref_name = name_for_collection_relationship(
                automap_base, referred_cls, local_cls, constraint
            )

            o2m_kws: Dict[str, Union[str, bool]] = {}
            nullable = False not in {fk.parent.nullable for fk in fks}
            if not nullable:
                o2m_kws["cascade"] = "all, delete-orphan"

                if (
                    constraint.ondelete
                    and constraint.ondelete.lower() == "cascade"
                ):
                    o2m_kws["passive_deletes"] = True
            else:
                if (
                    constraint.ondelete
                    and constraint.ondelete.lower() == "set null"
                ):
                    o2m_kws["passive_deletes"] = True

            create_backref = backref_name not in referred_cfg.properties