pythonのsqlalchemy外键关联查询

 #!/usr/bin/env python

 import sqlalchemy
 from sqlalchemy import create_engine
 from  sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import Column,Integer,String,DATE,Enum,ForeignKey
 from sqlalchemy.orm import sessionmaker,relationship

 # 创建连接 echo=True 就会打印出所有过程信息
 engine = create_engine("mysql+pymysql://root:root@localhost/testuser",encoding="utf-8",echo=True)

 #
 Base = declarative_base() # 生成orm基类

 class Student(Base):
     __tablename__ = "student"
     id = Column(Integer,primary_key=True)
     name = Column(String(32),nullable=False)
     register_Date = Column(DATE,nullable=False)

     def __repr__(self):
         return "<%s name:%s>"% (self.id,self.name)

 class StudyRecord(Base):
     __tablename__ = "study_record"
     id = Column(Integer, primary_key=True)
     day = Column(Integer,nullable=False)
     status = Column(String(32),nullable=False)
     stu_id = Column(Integer,ForeignKey("student.id"))

     # 关系
     student = relationship("Student",backref="my_study_record")
     def __repr__(self):
         return "< day:%s status:%s>" % (self.id, self.status)

 Base.metadata.create_all(engine) # 创建表结构

 Session_class = sessionmaker(bind=engine) # 创建与数据库的会话session class 注意，这里返回的是一个class，不是实例

 session = Session_class()

 # s1 = Student(name="Tom",register_Date="2018-08-08")
 # s2 = Student(name="Jerry",register_Date="2018-06-08")
 # s3 = Student(name="Lucy",register_Date="2018-08-28")
 # s4 = Student(name="Lily",register_Date="2018-08-18")
 #
 # study_obj1 = StudyRecord(day=1,status="Yes",stu_id=1)
 # study_obj2 = StudyRecord(day=2,status="No",stu_id=1)
 # study_obj3 = StudyRecord(day=3,status="Yes",stu_id=1)
 # study_obj4 = StudyRecord(day=1,status="Yes",stu_id=2)

 # session.add_all([s1,s2,s3,s4,study_obj1,study_obj2,study_obj3,study_obj4])
 # session.commit()

 stu_obj = session.query(Student).filter(Student.name=="Tom").first()

 print(stu_obj.my_study_record)

解释：

　　（1）创建表：将43-54行代码解封，此时会自动为您创建相关联的表

重点理解：

　　32行：student = relationship("Student",backref="my_study_record")

　　这里需要引入  from sqlalchemy.orm import sessionmaker,relationship

　　32行代码用途，可以通过Student 在表StudyRecord中直接引用表Student  那么可以通过 my_study_record 直接引用StudyRecord中的数据。这是因为他们两者存在外键关联，所以当我们执行第58行的时候，他就会根据外键去查询study_record 中的数据。