Postgres sequences detected with ::regclass cast

[ChrisLovering]

Describe the bug

When creating a non-primary key column with a sequence in postgres, alembic generates the migration as expected. However, after applying that migration, and then autogenerating a new revision, alembic sees that there is a ::regclass cast on the nextval() call, and tries to remove it in a migration.

Expected behavior

Alembic doesn't attempt to remove the ::regclass cast as it's added by postgres.

To Reproduce
Please try to provide a Minimal, Complete, and Verifiable example, with the migration script and/or the SQLAlchemy tables or models involved.
See also Reporting Bugs on the website.

Model:

class Post(Base):
    __tablename__ = "posts"

    post_id: Mapped[int] = mapped_column(BigInteger, primary_key=True)
    user_id: Mapped[int] = mapped_column(BigInteger, nullable=False, index=True)
    sequential_id_seq = Sequence("post_sequential_id_seq", metadata=Base.metadata, start=1)
    sequential_id: Mapped[int] = mapped_column(
        Integer,
        sequential_id_seq,
        server_default=sequential_id_seq.next_value(),
    )

Initial migration:

def upgrade() -> None:
    """Apply this migration."""
    # ### commands auto generated by Alembic - please adjust! ###
    op.execute(sa.schema.CreateSequence(sa.Sequence("post_sequential_id_seq", start=1)))
    op.create_table(
        "posts",
        sa.Column("post_id", sa.BigInteger(), nullable=False),
        sa.Column("user_id", sa.BigInteger(), nullable=False),
        sa.Column(
            "sequential_id", sa.Integer(),
            server_default=sa.text("nextval('post_sequential_id_seq')"),
            nullable=False,
        ),
        sa.PrimaryKeyConstraint("post_id", name=op.f("posts_pk")),
    )
    op.create_index(op.f("posts_user_id_ix"), "posts", ["user_id"], unique=False)
    # ### end Alembic commands ###

def downgrade() -> None:
    """Revert this migration."""
    # ### commands auto generated by Alembic - please adjust! ###
    op.drop_index(op.f("posts_user_id_ix"), table_name="posts")
    op.drop_table("posts")
    # ### end Alembic commands ###

Every subseqent migration:

def upgrade() -> None:
    """Apply this migration."""
    # ### commands auto generated by Alembic - please adjust! ###
    op.alter_column(
        "posts",
        "sequential_id",
        existing_type=sa.INTEGER(),
        server_default=sa.text("nextval('post_sequential_id_seq')"),
        existing_nullable=False,
    )
    # ### end Alembic commands ###


def downgrade() -> None:
    """Revert this migration."""
    # ### commands auto generated by Alembic - please adjust! ###
    op.alter_column(
        "posts",
        "sequential_id",
        existing_type=sa.INTEGER(),
        server_default=sa.text("nextval('post_sequential_id_seq'::regclass)"),
        existing_nullable=False,
    )
    # ### end Alembic commands ###

Versions.

• OS: debian:bookworm-slim Docker image (via python:3-slim)
• Python: 3.12
• Alembic: 1.13.2
• SQLAlchemy: 2.0.31
• Database: PostgreSQL 16
• DBAPI: postgresql+psycopg_async

Additional context

I found this code which seems to handle ::regclass, however based on the log.info below I am assuming this only handles serial primary key sequences, but I may be wrong.
Have a nice day!

[zzzeek]

@CaselIT can you triage this?

[CaselIT]

yes, sorry. seems like a bug, will need to look at what to do here.