Alembic: How to migrate custom type in a model?

Question

My User model is

class User(UserMixin, db.Model):
    __tablename__ = 'users'
    # noinspection PyShadowingBuiltins
    uuid = Column('uuid', GUID(), default=uuid.uuid4, primary_key=True,
                  unique=True)
    email = Column('email', String, nullable=False, unique=True)
    _password = Column('password', String, nullable=False)
    created_on = Column('created_on', sa.types.DateTime(timezone=True),
                        default=datetime.utcnow())
    last_login = Column('last_login', sa.types.DateTime(timezone=True),
                        onupdate=datetime.utcnow())

where GUID is a custom type as described in sqlalchemy docs (Exactly same)

Now when I run

alembic revision --autogenerate -m "Added initial table"

I get my upgrade() as

def upgrade():
    ### commands auto generated by Alembic - please adjust! ###
    op.create_table('users',
    sa.Column('uuid', sa.GUID(), nullable=False),
    sa.Column('email', sa.String(), nullable=False),
    sa.Column('password', sa.String(), nullable=False),
    sa.Column('created_on', sa.DateTime(timezone=True), nullable=True),
    sa.Column('last_login', sa.DateTime(timezone=True), nullable=True),
    sa.PrimaryKeyConstraint('uuid'),
    sa.UniqueConstraint('email'),
    sa.UniqueConstraint('uuid')
    )
    ### end Alembic commands ###

but during applying upgrade -> alembic upgrade head, I see

File "alembic/versions/49cc74d0da9d_added_initial_table.py", line 20, in upgrade
    sa.Column('uuid', sa.GUID(), nullable=False),
AttributeError: 'module' object has no attribute 'GUID'

How can I make it work with GUID/custom type here?

Answer 1

You can replace sa.GUID() with either sa.CHAR(32) or UUID() (after adding the import line from sqlalchemy.dialects.postgresql import UUID) depending on the dialect.

Replacing it with GUID() (after adding the import line from your.models.custom_types import GUID) will work also, but then the upgrade script is tied to your model code, which may not be a good thing.