Flask ImportError：无法导入名称

Question

您好我想在模型中导入模型。但是，如果两个模型相互导入，我似乎无法做到这一点。下面要说明的是示例代码

# Files located in models with filename model_b.py
from repository.base_model import BaseModel
from models.model_a import ModelA

class ModelB(BaseModel):
     # properties and classes here
     # There's a join function here that make use of ModelA

现在我有另一个名为model_a的文件，它有一个ModelA类。我需要导入ModelB，因为我需要进行连接查询。

# Files located in models with filename model_a.py
from repository.base_model import BaseModel
from models.model_b import ModelB

class ModelA(BaseModel):
     # properties and classes here
    def join_function(code, session):

      result = (session.query(ModelA).
                select_from(ModelA).
                join(ModelB, ModelB.id == ModelA.model_b_id).
                filter(ModelB.code == code).
                all())

如果我运行我的脚本，请说

  

ImportError：无法导入名称'ModelB'

现在，如果我删除了ModelB的导入，它就可以了。当两个模型相互导入时似乎存在问题。有解决方案吗？