數據庫：

聯表查詢：

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column,String,Integer
from sqlalchemy.orm import sessionmaker


engine = create_engine("mysql+pymysql://root:mysql8@localhost/mysqltest")
Base = declarative_base()

class Student(Base):
    
 
__tablename__ = ‘student‘
    id = Column(Integer, primary_key=True)
    name = Column(String(32))
    sex = Column(String(32))
    def __repr__(self):
        return "%s,%s,%s" %(self.id, self.name, self.sex)

class Study_record(Base):
    __tablename__ = ‘study_record‘
    id = Column(Integer, primary_key=True)
    day 
 
= Column(Integer)
    status = Column(String(32))
    stu_id = Column(Integer)
    def __repr__(self):
        return "%s,%s,%s" %(self.day, self.status, self.stu_id)

Session_class = sessionmaker(bind=engine)
session = Session_class()

# select a.*,b.* from a,b where a.id=b.s_id
result = session.query(Student, Study_record).filter(Student.id==Study_record.stu_id).all()
 
print(result)  # [(1,alex,男, 1,YES,1), (1,alex,男, 2,NO,1), (2,jack,男, 1,YES,2), (2,jack,男, 2,YES,2)]
# 此處報錯！！有外鍵關聯的時候才能用，而且外鍵也需要用類映射出來。真TM麻煩！
result1 = session.query(Student).join(Study_record).all()
print(result1)

外鍵關聯之雙向反查：

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

engine = create_engine("mysql+pymysql://root:mysql8@localhost/mysqltest")
Base = declarative_base()

#   學員表student跟考勤表study_record是一對多的關系
class Student(Base):
    __tablename__ = ‘student‘
    id = Column(Integer, primary_key=True)
    name = Column(String(32))
    sex = Column(String(32))
    def __repr__(self):
        return "%s,%s,%s" %(self.id, self.name, self.sex)

class Study_record(Base):
    __tablename__ = ‘study_record‘
    id = Column(Integer, primary_key=True)
    day = Column(Integer)
    status = Column(String(32))
    stu_id = Column(Integer, ForeignKey(‘student.id‘))
    # 雙向反查關系，通過student字段可以看記錄對應的學生，反過來通過my_study_record可看學生對應的記錄
    student = relationship("Student", backref="my_study_record")
    def __repr__(self):   # self.student.name  這是它的牛逼之處：
        return "%s,%s,%s" %(self.day, self.status, self.student.name)

Session_class = sessionmaker(bind=engine)
session = Session_class()

# 上面加了外鍵關聯，可以用了
result1 = session.query(Student).join(Study_record, isouter=True).all()
print(result1)  # [1,alex,男, 2,jack,男, 3,rose,女]

alex = session.query(Student).filter(Student.name == ‘alex‘).first()
print(alex)  # 1,alex,男
# 如果想查Alex的上課記錄咋查呢？在上面加一個雙向反查關系
print(alex.my_study_record)  # [1,YES,alex, 2,NO,alex]

顧客表有兩個外鍵，兩個外鍵指向同一張表，此時的雙向查詢：

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

engine = create_engine("mysql+pymysql://root:mysql8@localhost/mysqltest")
Base = declarative_base()

# 顧客表Customer有兩個外鍵，訂單地址ID，郵寄地址ID。都關聯了同一張表
class Customer(Base):
    __tablename__ = ‘customer‘
    id = Column(Integer, primary_key=True)
    name = Column(String(32))

    bill_addr_id = Column(Integer, ForeignKey("address.id"))
    post_addr_id = Column(Integer, ForeignKey("address.id"))

    bill_addr = relationship("Address", foreign_keys=[bill_addr_id], backref="bill_customers")
    post_addr = relationship("Address", foreign_keys=[post_addr_id], backref="post_customers")

    def __repr__(self):
        return "%s" %(self.name)

class Address(Base):
    __tablename__ = ‘address‘
    id = Column(Integer, primary_key=True)
    detail_address = Column(String(32))
    def __repr__(self):
        return "%s" %(self.detail_address)

Base.metadata.create_all(engine)

from sqlalchemy.orm import sessionmaker
import orms

Session_class = sessionmaker(bind=orms.engine)
session = Session_class()
a1 = orms.Address(detail_address="BeiJing")
a2 = orms.Address(detail_address="ShangHai")
a3 = orms.Address(detail_address="TianJin")

session.add_all([a1, a2, a3])
# 註意這裏賦值的牛逼之處！！！直接用對象進行賦值
c1 = orms.Customer(name="Alex", bill_addr=a1, post_addr=a2)
c2 = orms.Customer(name="Jack", bill_addr=a2, post_addr=a3)
c3 = orms.Customer(name="Rain", bill_addr=a3, post_addr=a3)

session.add_all([c1, c2, c3])
session.commit()

from sqlalchemy.orm import sessionmaker
import orms

Session_class = sessionmaker(bind=orms.engine)
session = Session_class()

alex = session.query(orms.Customer).filter(orms.Customer.name=="Alex").first()
print(alex.bill_addr, alex.post_addr)  # BeiJing ShangHai

sh = session.query(orms.Address).filter(orms.Address.detail_address=="ShangHai").first()
print(sh.bill_customers)  # [Jack]

sqlalchemy外鍵的一些東西