新增databases.py把所有建表基类统一成一个，才可以链接外键。

students/model/students_model.py

@@ -1,13 +1,15 @@
 # students_model处理数据库模型
 import datetime
 
-from students.databases import *
+from databases import engine_all,Base_all,Session
+from sqlalchemy import *
+# from students.databases import *
 from datetime import datetime
 from sqlalchemy.dialects.mysql import DATETIME
 from students.schema.students_request import SexEnum , EducationEnum
-from sqlalchemy import Enum
+from sqlalchemy import Enum,ForeignKey,Integer,String
 
-class Students(Base):
+class Students(Base_all):
     __tablename__ = 'students'
     id = Column(Integer
                  , primary_key=True
@@ -53,10 +55,12 @@ class Students(Base):
 
     # 外键字段
     class_id = Column(Integer
-                 , comment='学生班级'
-                 , nullable=False )
+                      , ForeignKey("classes.id")
+                      , comment='学生班级'
+                      , nullable=False )
 
     advisor_id = Column(Integer
+                        , ForeignKey("teachers.id")
                         , comment='顾问ID')
 
     # 额外字段