Class CheckFirst

lib/sqlalchemy/sql/ddl.py:1300–1344

Enumeration for the :paramref:`.MetaData.create_all.checkfirst` parameter passed to methods like :meth:`.MetaData.create_all`, :meth:`.MetaData.drop_all`, :meth:`.Table.create`, :meth:`.Table.drop` and others. This enumeration indicates what kinds of objects should be "checked"

class CheckFirst(Flag):
    """Enumeration for the :paramref:`.MetaData.create_all.checkfirst`
    parameter passed to methods like :meth:`.MetaData.create_all`,
    :meth:`.MetaData.drop_all`, :meth:`.Table.create`, :meth:`.Table.drop` and
    others.

    This enumeration indicates what kinds of objects should be "checked"
    with a separate query before emitting CREATE or DROP for that object.

    Can use ``CheckFirst(bool_value)`` to convert from a boolean value.

    .. versionadded:: 2.1

    """

    NONE = 0  # equivalent to False
    """No items should be checked"""

    # avoid 1 so that bool True doesn't match by value
    TABLES = 2
    """Check for tables"""

    VIEWS = auto()
    """Check for views"""

    INDEXES = auto()
    """Check for indexes"""

    SEQUENCES = auto()
    """Check for sequences"""

    TYPES = auto()
    """Check for custom datatypes that are created server-side

    This is currently used by PostgreSQL.

    """

    ALL = TABLES | VIEWS | INDEXES | SEQUENCES | TYPES  # equivalent to True

    @classmethod
    def _missing_(cls, value: object) -> Any:
        if isinstance(value, bool):
            return cls.ALL if value else cls.NONE
        return super()._missing_(value)


class SchemaGenerator(InvokeCreateDDLBase):