Do not downgrade to unique index if nonunique data present

"""

import logging

from alembic import op

from sqlalchemy import text

from galaxy.model.database_object_names import build_index_name

from galaxy.model.migrations.util import (

    alter_column,

    transaction,

)

log = logging.getLogger(__name__)

# revision identifiers, used by Alembic.

revision = "9a5207190a4d"

down_revision = "a99a5b52ccb8"

def downgrade():

    with transaction():

        drop_index(index_name, table_name)

        alter_column(table_name, column_name, nullable=True)

        stmt = text("SELECT 1 FROM role GROUP BY name HAVING count(*) > 1")

        has_nonunique_values = op.get_bind().scalar(stmt)

        if not has_nonunique_values:

            drop_index(index_name, table_name)

            create_index(index_name, table_name, [column_name], unique=True)

        else:

            msg = f"""This downgrade requires creating a unique index on the `{table_name}.{column_name}` field.

This operation cannot proceed due to the existence of non-unique values in that column, which are the result of Galaxy v24.2 (and above)

operating under normal conditions. The current non-unique index will remain unchanged."""

            log.error(msg)