code: def upgrade():
      conn = op.get_bind()
      if isinstance(conn.dialect, postgresql.dialect):
          conn.execute(
              'ALTER TABLE "tagged_object" ALTER COLUMN "object_type" TYPE VARCHAR'
          )
          conn.execute(
              'ALTER TABLE "tag" ALTER COLUMN "type" TYPE VARCHAR'
          )
          conn.execute("DROP TYPE IF EXISTS objecttypes")
          conn.execute("DROP TYPE IF EXISTS tagtypes")
  
imports: from alembic import op
  from sqlalchemy.dialects import postgresql
label_desc: Use image node_id 1 for calling a global function with example usage: upgrade() without return types