Altering an Enum field using Alembic

I decided to try to follow the postgres approach as directly as possible and came up with the following migration.

from alembic import opimport sqlalchemy as saold_options = ('nonexistent_executable', 'signal', 'success', 'timed_out')new_options = sorted(old_options + ('output_limit_exceeded',))old_type = sa.Enum(*old_options, name='status')new_type = sa.Enum(*new_options, name='status')tmp_type = sa.Enum(*new_options, name='_status')tcr = sa.sql.table('testcaseresult',                   sa.Column('status', new_type, nullable=False))def upgrade():    # Create a tempoary "_status" type, convert and drop the "old" type    tmp_type.create(op.get_bind(), checkfirst=False)    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE _status'               ' USING status::text::_status')    old_type.drop(op.get_bind(), checkfirst=False)    # Create and convert to the "new" status type    new_type.create(op.get_bind(), checkfirst=False)    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE status'               ' USING status::text::status')    tmp_type.drop(op.get_bind(), checkfirst=False)def downgrade():    # Convert 'output_limit_exceeded' status into 'timed_out'    op.execute(tcr.update().where(tcr.c.status==u'output_limit_exceeded')               .values(status='timed_out'))    # Create a tempoary "_status" type, convert and drop the "new" type    tmp_type.create(op.get_bind(), checkfirst=False)    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE _status'               ' USING status::text::_status')    new_type.drop(op.get_bind(), checkfirst=False)    # Create and convert to the "old" status type    old_type.create(op.get_bind(), checkfirst=False)    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE status'               ' USING status::text::status')    tmp_type.drop(op.get_bind(), checkfirst=False)

It appears that alembic has no direct support for the USING statement in its alter_table method.

I used a bit simpler approach with less steps than the accepted answer, which I based this on. In this example I will pretend the enum in question is called 'status_enum', because in the accepted answer the use of 'status' for both the column and enum confused me.

from alembic import op import sqlalchemy as saname = 'status_enum'tmp_name = 'tmp_' + nameold_options = ('nonexistent_executable', 'signal', 'success', 'timed_out')new_options = sorted(old_options + ('output_limit_exceeded',))new_type = sa.Enum(*new_options, name=name)old_type = sa.Enum(*old_options, name=name)tcr = sa.sql.table('testcaseresult',                   sa.Column('status', new_type, nullable=False))def upgrade():    op.execute('ALTER TYPE ' + name + ' RENAME TO ' + tmp_name)    new_type.create(op.get_bind())    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status ' +               'TYPE ' + name + ' USING status::text::' + name)    op.execute('DROP TYPE ' + tmp_name)def downgrade():    # Convert 'output_limit_exceeded' status into 'timed_out'                                                                                                                          op.execute(tcr.update().where(tcr.c.status=='output_limit_exceeded')               .values(status='timed_out'))    op.execute('ALTER TYPE ' + name + ' RENAME TO ' + tmp_name)    old_type.create(op.get_bind())    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status ' +               'TYPE ' + name + ' USING status::text::' + name)    op.execute('DROP TYPE ' + tmp_name)

This runs without problems:

from alembic import opdef upgrade():    op.execute("COMMIT")    op.execute("ALTER TYPE enum_type ADD VALUE 'new_value'")def downgrade():    ...

Reference