提示错误：
sqlalchemy.exc.NoForeignKeysError: Could not determine join condition between parent/child tables on relationship Answer.answer_collection - there are no foreign keys linking these tables via secondary table 'answers_collections'. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify 'primaryjoin' and 'secondaryjoin' expressions.自己解决了，运行文件中没有导入的缘故。