Method visit_metadata

lib/sqlalchemy/sql/ddl.py:1539–1615

(self, metadata)

        self.memo = {}

    def visit_metadata(self, metadata):
        if self.tables is not None:
            tables = self.tables
        else:
            tables = list(metadata.tables.values())

        try:
            unsorted_tables = [t for t in tables if self._can_drop_table(t)]
            collection = list(
                reversed(
                    sort_tables_and_constraints(
                        unsorted_tables,
                        filter_fn=lambda constraint: (
                            False
                            if not self.dialect.supports_alter
                            or constraint.name is None
                            else None
                        ),
                    )
                )
            )
        except exc.CircularDependencyError as err2:
            if not self.dialect.supports_alter:
                util.warn(
                    "Can't sort tables for DROP; an "
                    "unresolvable foreign key "
                    "dependency exists between tables: %s; and backend does "
                    "not support ALTER.  To restore at least a partial sort, "
                    "apply use_alter=True to ForeignKey and "
                    "ForeignKeyConstraint "
                    "objects involved in the cycle to mark these as known "
                    "cycles that will be ignored."
                    % (", ".join(sorted([t.fullname for t in err2.cycles])))
                )
                collection = [(t, ()) for t in unsorted_tables]
            else:
                raise exc.CircularDependencyError(
                    err2.args[0],
                    err2.cycles,
                    err2.edges,
                    msg="Can't sort tables for DROP; an "
                    "unresolvable foreign key "
                    "dependency exists between tables: %s.  Please ensure "
                    "that the ForeignKey and ForeignKeyConstraint objects "
                    "involved in the cycle have "
                    "names so that they can be dropped using "
                    "DROP CONSTRAINT."
                    % (", ".join(sorted([t.fullname for t in err2.cycles]))),
                ) from err2

        seq_coll = [
            s
            for s in metadata._sequences.values()
            if self._can_drop_sequence(s)
        ]

        event_collection = [t for (t, fks) in collection if t is not None]