sqlalchemy.dialects.postgresql.ENUM

PostgreSQL ENUM type.

This is a subclass of _types.Enum which includes support for PG's CREATE TYPE and DROP TYPE.

When the builtin type _types.Enum is used and the :paramref:`.Enum.native_enum` flag is left at its default of True, the PostgreSQL backend will use a _postgresql.ENUM type as the implementation, so the special create/drop rules will be used.

The create/drop behavior of ENUM is necessarily intricate, due to the awkward relationship the ENUM type has in relationship to the parent table, in that it may be "owned" by just a single table, or may be shared among many tables.

When using _types.Enum or _postgresql.ENUM in an "inline" fashion, the CREATE TYPE and DROP TYPE is emitted corresponding to when the _schema.Table.create and _schema.Table.drop methods are called:

table = Table('sometable', metadata,
    Column('some_enum', ENUM('a', 'b', 'c', name='myenum'))
)

table.create(engine)  # will emit CREATE ENUM and CREATE TABLE
table.drop(engine)  # will emit DROP TABLE and DROP ENUM

To use a common enumerated type between multiple tables, the best practice is to declare the _types.Enum or _postgresql.ENUM independently, and associate it with the _schema.MetaData object itself:

my_enum = ENUM('a', 'b', 'c', name='myenum', metadata=metadata)

t1 = Table('sometable_one', metadata,
    Column('some_enum', myenum)
)

t2 = Table('sometable_two', metadata,
    Column('some_enum', myenum)
)

When this pattern is used, care must still be taken at the level of individual table creates. Emitting CREATE TABLE without also specifying checkfirst=True will still cause issues:

t1.create(engine) # will fail: no such type 'myenum'

If we specify checkfirst=True, the individual table-level create operation will check for the ENUM and create if not exists:

# will check if enum exists, and emit CREATE TYPE if not
t1.create(engine, checkfirst=True)

When using a metadata-level ENUM type, the type will always be created and dropped if either the metadata-wide create/drop is called:

metadata.create_all(engine)  # will emit CREATE TYPE
metadata.drop_all(engine)  # will emit DROP TYPE

The type can also be created and dropped directly:

my_enum.create(engine)
my_enum.drop(engine)