Class Enum

lib/sqlalchemy/sql/sqltypes.py:1367–1984

Generic Enum Type. The :class:`.Enum` type provides a set of possible string values which the column is constrained towards. The :class:`.Enum` type will make use of the backend's native "ENUM" type if one is available; otherwise, it uses a VARCHAR datatype. An option also exis

class Enum(String, SchemaType, Emulated, TypeEngine[Union[str, enum.Enum]]):
    """Generic Enum Type.

    The :class:`.Enum` type provides a set of possible string values
    which the column is constrained towards.

    The :class:`.Enum` type will make use of the backend's native "ENUM"
    type if one is available; otherwise, it uses a VARCHAR datatype.
    An option also exists to automatically produce a CHECK constraint
    when the VARCHAR (so called "non-native") variant is produced;
    see the  :paramref:`.Enum.create_constraint` flag.

    The :class:`.Enum` type also provides in-Python validation of string
    values during both read and write operations.  When reading a value
    from the database in a result set, the string value is always checked
    against the list of possible values and a ``LookupError`` is raised
    if no match is found.  When passing a value to the database as a
    plain string within a SQL statement, if the
    :paramref:`.Enum.validate_strings` parameter is
    set to True, a ``LookupError`` is raised for any string value that's
    not located in the given list of possible values; note that this
    impacts usage of LIKE expressions with enumerated values (an unusual
    use case).

    The source of enumerated values may be a list of string values, or
    alternatively a PEP-435-compliant enumerated class.  For the purposes
    of the :class:`.Enum` datatype, this class need only provide a
    ``__members__`` method.

    When using an enumerated class, the enumerated objects are used
    both for input and output, rather than strings as is the case with
    a plain-string enumerated type::

        import enum
        from sqlalchemy import Enum


        class MyEnum(enum.Enum):
            one = 1
            two = 2
            three = 3


        t = Table("data", MetaData(), Column("value", Enum(MyEnum)))

        connection.execute(t.insert(), {"value": MyEnum.two})
        assert connection.scalar(t.select()) is MyEnum.two

    Above, the string names of each element, e.g. "one", "two", "three",
    are persisted to the database; the values of the Python Enum, here
    indicated as integers, are **not** used; the value of each enum can
    therefore be any kind of Python object whether or not it is persistable.

    In order to persist the values and not the names, the
    :paramref:`.Enum.values_callable` parameter may be used.   The value of
    this parameter is a user-supplied callable, which  is intended to be used
    with a PEP-435-compliant enumerated class and  returns a list of string
    values to be persisted.   For a simple enumeration that uses string values,