一对多；一对一
# one -- many class Students(Base): __tablename__ = "students" sid = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer) tid = Column(Integer, ForeignKey("teachers.tid")) # 声明字段值受到另一个表的字段值得约束，注意是<表名> tec = relationship("Teachers", backref=‘std‘) # 注意只能类名，backref可以单独写，back_populates必须成对出现 def __str__(self): return self.name class Teachers(Base): __tablename__ = "teachers" tid = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer) def __str__(self): return self.name Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # 添加数据/关系 # 方法一 # t_1 = Teachers(name=‘t_1‘) # t_2 = Teachers(name=‘t_2‘) # session.add_all([t_1, t_2]) # session.commit() # # s_1 = Students(name="s_1", tid=t_1.tid) # s_2 = Students(name=‘s_2‘, tid=t_1.tid) # # session.add_all([s_1, s_2]) # session.commit() # 方法二 # t_1 = Teachers(name=‘t_1‘) # t_2 = Teachers(name=‘t_2‘) # s_1 = Students(name="s_1") # s_2 = Students(name=‘s_2‘) # t_1.std=[s_1,s_2] # t_2.std=[s_2] # session.add_all([t_1, t_2]) # 1.会自动添加s_1,s_2; 2.会自动建立关系 # session.commit() # 方法三 s_3 = Students(name=‘s_3‘) t_1_q = session.query(Teachers).filter_by(name=‘t_1‘).first() t_1_q.std.append(s_3) session.commit() ### 删除 class Teachers(Base): __tablename__ = "teachers" tid = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer) # std = relationship("Students", back_populates=‘tec‘,cascade=‘all,delete-orphan‘) # 当使用back_populates时,级联删除标识只能写在这里；后期添加依然生效,但不建议； def __str__(self): return self.name class Students(Base): __tablename__ = "students" sid = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer) tid = Column(Integer, ForeignKey("teachers.tid")) # tec = relationship("Teachers", back_populates=‘std‘) # tec = relationship("Teachers", backref=‘std‘,cascade=‘all,delete-orphan‘) # error tec = relationship("Teachers", backref=backref(‘std‘,cascade=‘all,delete-orphan‘)) # 如果使用backref那么只能这种写法,同时级联删除标识写在此处,后期添加依旧有效,但不建议 def __str__(self): return self.name # one -- many ###非级联删除 # t_1 = Teachers(name=‘t1‘, age=18) # session.add(t_1) # session.commit() # 如果不提交，那么 t_1 是没有ID的，所以该对象不能使用，如果非要在不提交的情况下使用，那么可以使用query(t_1) 得到一个对象，赋予它id # s_1 = Students(name=‘s1‘, tid=t_1.tid) # s_2 = Students(name=‘s2‘, tid=t_1.tid) # session.add_all([s_1, s_2]) # session.commit() # t_1 = session.query(Teachers).filter_by(name=‘t1‘).first() # session.delete(t_1) # 默认非级联删除.即：1.删除1的部分后,多的部分的相关字段自动置为Null;此例中：删除老师之后，学生的tid字段变为了NULL # session.commit() # s_1 = session.query(Students).filter_by(name=‘s1‘).first() # s_2 = session.query(Students).filter_by(name=‘s2‘).delete() # session.delete(s_1) # 删除多的部分之后, 1 的部分不受影响.此例中：删除学生之后,教师表不受任何影响. # session.commit() ### 级联删除 class Students(Base): __tablename__ = "students" sid = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer) tid = Column(Integer, ForeignKey("teachers.tid")) # 声明字段值受到另一个表的字段值得约束，注意是<表名> # tec = relationship("Teachers", backref = backref(‘std‘,cascade="delete,delete-orphan")) # 注意只能类名，backref可以单独写，back_populates必须成对出现 # tec = relationship("Teachers", backref = backref(‘std‘,cascade="all,delete-orphan")) # 注意只能类名，backref可以单独写，back_populates必须成对出现 tec = relationship("Teachers", backref = backref(‘std‘,cascade="all,delete,delete-orphan")) # 注意只能类名，backref可以单独写，back_populates必须成对出现 # tec = relationship("Teachers", backref = backref(‘std‘,cascade="delete-orphan")) # error def __str__(self): return self.name class Teachers(Base): __tablename__ = "teachers" tid = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer) def __str__(self): return self.name # Base.metadata.drop_all(engine) Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() #####one -- many # t_1 = Teachers(name=‘t1‘, age=18) # session.add(t_1) # session.commit() # 如果不提交，那么 t_1 是没有ID的，所以该对象不能使用，如果非要在不提交的情况下使用，那么可以使用query(t_1) 得到一个对象，赋予它id # s_1 = Students(name=‘s1‘, tid=t_1.tid) # s_2 = Students(name=‘s2‘, tid=t_1.tid) # session.add_all([s_1, s_2]) # session.commit() t_1 = session.query(Teachers).filter_by(name=‘t1‘).first() session.delete(t_1) # 当在relationship字段中设置了 cascade 属性之后，就会变为级联删除 session.commit() ### one -- one ## 在 one 一方(即没有FK字段的一方）的 relationship 增加参数 uselist=False class Parent(Base): __tablename__ = ‘parent‘ id = Column(Integer, primary_key=True) name = Column(String(30)) child = relationship("Child", uselist=False, back_populates="parent") class Child(Base): __tablename__ = ‘child‘ id = Column(Integer, primary_key=True) name = Column(String(30)) parent_id = Column(Integer, ForeignKey(‘parent.id‘)) parent = relationship("Parent", back_populates="child") # Base.metadata.drop_all(engine) Base.metadata.create_all(engine) Session = sessionmaker(engine) sess = Session() # p_1 = Parent(name="p_1") # sess.add(p_1) # sess.commit() # c_1 = Child(name="c_1", parent_id=p_1.id) # sess.add_all([c_1]) # sess.commit() # c_2 = Child(name=‘c_2‘,parent_id=p_1.id) # sess.add(c_2) # sess.commit() # 虽然指定了 uselist为False,但是还是可以对同一个对象进行多次外键链接的。 # 虽然有多个外键链接,但是查找的时候,也只会显示第一个,并不会报错. p_1_q = sess.query(Parent).filter_by(name=‘p_1‘).first() print(p_1_q.name) print(p_1_q.child) ### one -- one another class Parent(Base): __tablename__ = ‘parent‘ id = Column(Integer, primary_key=True) name = Column(String(3)) child_id = Column(Integer, ForeignKey(‘child.id‘)) child = relationship("Child", back_populates="parent") class Child(Base): __tablename__ = ‘child‘ id = Column(Integer, primary_key=True) name = Column(String(3)) parent = relationship("Parent", back_populates="child", uselist=False) Base.metadata.drop_all(engine) Base.metadata.create_all(engine) c_1 = Child(name="c_1") sess.add(c_1) sess.commit() p_1 = Parent(name="p_1",child_id=c_1.id) p_2 = Parent(name="p_2",child_id=c_1.id) sess.add_all([p_1, p_2]) sess.commit() c_1_q = sess.query(Child).filter_by(name=‘c_1‘).first() print(c_1_q.name) print(c_1_q.parent) # 利用 unique 建立真正的 one -- one 关系 class Parent(Base): __tablename__ = ‘parent‘ id = Column(Integer, primary_key=True) name = Column(String(30)) child = relationship("Child", uselist=False, back_populates="parent") class Child(Base): __tablename__ = ‘child‘ id = Column(Integer, primary_key=True) name = Column(String(30)) parent_id = Column(Integer, ForeignKey(‘parent.id‘),unique=True) # 通过限制外键的唯一性来真正建立一对一的关系 parent = relationship("Parent", back_populates="child") # Base.metadata.drop_all(engine) Base.metadata.create_all(engine) Session = sessionmaker(engine) sess = Session() # p_1 = Parent(name="p_1") # sess.add(p_1) # sess.commit() # c_1 = Child(name="c_1", parent_id=p_1.id) # sess.add_all([c_1]) # sess.commit() p_1_q = sess.query(Parent).filter_by(name=‘p_1‘).first() print(p_1_q.child.name) # c_2 = Child(name=‘c_2‘,parent_id=p_1_q.id) # sess.add(c_2) # sess.commit() # error 因为 unique的存在 # p_2 = Parent(name=‘p_2‘) # sess.add(p_2) # sess.commit() # c_2 = Child(name=‘c_2‘,parent_id=p_2.id) # sess.add(c_2) # sess.commit() # 修改关系 # t_1 = Teachers(name=‘t1‘, age=18) # t_2 = Teachers(name=‘t2‘, age=20) # session.add(t_1) # session.add(t_2) # session.commit() # 如果不提交，那么 t_1 是没有ID的，所以该对象不能使用，如果非要在不提交的情况下使用，那么可以使用query(t_1) 得到一个对象，赋予它id # s_1 = Students(name=‘s1‘, tid=t_1.tid) # s_2 = Students(name=‘s2‘, tid=t_1.tid) # session.add_all([s_1, s_2]) # session.commit() # 删除关系 # t_1_q = session.query(Teachers).filter_by(name=‘t1‘).first() # for i in t_1_q.std: # t_1_q.std 是一个列表，我们可以以python的方式来删除其中的元素 # print(i.name) # # s_1 = t_1_q.std.pop() # # print(s_1.name) # # session.commit() # 再次查看 学生表，会发现 学生 s2 的老师一栏变为了null 这说明，删除的只是 二者之间的关系 # s_2 = session.query(Students).filter_by(name=‘s1‘).first() # t_1_q.std.remove(s_2) # session.commit() # # 再次查看 学生表，会发现 学生 s2 的老师一栏变为了null 这说明，删除的只是 二者之间的关系 # print(len(t_1_q.std)) # 另外一种删除关系的方式 ：直接修改学生的关系属性 # s_1 = session.query(Students).filter_by(name=‘s1‘).first() # s_1.tid = None # session.commit() # t_1_q = session.query(Teachers).filter_by(name=‘t1‘).first() # for i in t_1_q.std: # print(i.name) # 添加关系 # 指定学生的外键来 建立学生 -教师关系 # t_2_q = session.query(Teachers).filter_by(name=‘t2‘).first() # s_4= Students(name=‘s4‘,tid=t_2_q.tid) # session.add(s_4) # session.commit() # for i in t_2_q.std: # print(i.name) # 另一种建立师-生关系的方式 # s_3 = Students(name=‘s3‘) # 我们并没有指定学生的id # session.add(s_3) # session.commit() # t_2_q = session.query(Teachers).filter_by(name=‘t2‘).first() # s_3_q = session.query(Students).filter_by(name=‘s3‘).first() # print(t_2_q.name) # print(s_3_q.name) # for i in t_2_q.std: # print(i.name) # t_2_q.std.append(s_3_q) # 我们可以通过修改教师的std属性（利用列表的方式）来增加 实现学生-教师之间的关系，进而发现学生的tid属性也发生了更改 # print("___"*30) # for i in t_2_q.std: # print(i.name) # session.commit()
多表查询
class Students(Base): __tablename__ = "students" sid = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer) math = Column(Integer) tid = Column(Integer, ForeignKey("teachers.tid")) # 声明字段值受到另一个表的字段值得约束，注意是<表名> tec = relationship("Teachers", backref=‘std‘) # 注意只能类名，backref可以单独写，back_populates必须成对出现 def __str__(self): return self.name class Teachers(Base): __tablename__ = "teachers" tid = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer) def __str__(self): return self.name Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # t_1 = Teachers(name=‘t1‘,age=28) # t_2 = Teachers(name=‘t2‘,age=29) # session.add_all([t_1, t_2]) # session.commit() # s_1 = Students(name=‘s1‘,age=10,math=50,tid=t_1.tid) # s_2 = Students(name=‘s2‘,age=20,math=70,tid=t_1.tid) # s_3 = Students(name=‘s3‘,age=22,math=40,tid=t_2.tid) # s_4 = Students(name=‘s4‘,age=20,math=80,tid=t_2.tid) # session.add_all([s_1, s_2, s_3, s_4]) # session.commit() # join 连表查询 # q_1 = session.query(Students).join(Teachers).filter(Students.math>60).all() # q_2 = session.query(Students.name,Teachers.name).join(Teachers).filter(Students.math>60).all() # for i in q_1: # print(i.name) # for i in q_2: # print(i) # contains # s_1_q = session.query(Students).filter(Students.math==80).one() # print(s_1_q) # t_1_q = session.query(Teachers).filter(Teachers.std.contains(s_1_q)).one() # print(t_1_q.name) # any == # t_2_q = session.query(Teachers).filter(Teachers.std.any(Students.math == 80)).all() # for i in t_2_q: # print(i.name) # any = # t_3_q = session.query(Teachers).filter(Teachers.std.any(math=80)).one() # print(t_3_q.name) # 查找同类型的其他记录 # s_3_q = session.query(Students).filter(Students.tec.has(Teachers.tid==1)).all() # for i in s_3_q: # print(i.name) # t_4_q = session.query(Teachers).filter_by(tid=1).one() # print(t_4_q) # s_4_q = session.query(Students).with_parent(t_4_q).all() # for i in s_4_q: # print(i.name)
多对多关系
第一种
tec_std = Table("tec_std_rel", Base.metadata, Column("tec_id", ForeignKey("teachers.tid"), primary_key=True), Column("std_id", ForeignKey("students.sid"), primary_key=True) ) class Teacher(Base): __tablename__ = "teachers" tid = Column(Integer, primary_key=True) name = Column(String(30)) subject = Column(String(10)) students = relationship("Student", secondary=tec_std, # 可以使用表的变量名 back_populates="teachers") def __str__(self): return self.name class Student(Base): __tablename__ = "students" sid = Column(Integer, primary_key=True) name = Column(String(30)) math = Column(Integer) teachers = relationship("Teacher", secondary="tec_std_rel", # 也可以使用表名 back_populates="students") def __str__(self): return self.name Base.metadata.drop_all(engine) Base.metadata.create_all(engine) Session = sessionmaker(engine) sess = Session() lilei = Teacher(name=‘lilei‘,subject=‘math‘) hanmeimei = Teacher(name=‘hanmeimei‘, subject=‘chinese‘) xiaohong = Student(name=‘xiaohong‘,math=80) xiaoming = Student(name=‘xiaoming‘,math=90) xiaogang = Student(name=‘xiaogang‘,math=70) # 添加记录/关系 lilei.students = [xiaohong, xiaogang] lilei.students.append(xiaoming) hanmeimei.students.extend([xiaohong,xiaogang,xiaoming]) # 以上方式都会自动添加相关记录 sess.add(hanmeimei) sess.add(lilei) sess.commit() # lilei_q = sess.query(Teacher).filter_by(name=‘lilei‘).one() # xiaogang.teachers.append(lilei_q) # 注意：这里如果直接使用上面的变量lilei那么会在teachers表中增加新的一条记录。 # sess.add(xiaogang) # sess.commit() # 这种方式也可以添加相关记录 # 删除关系 # lilei_q = sess.query(Teacher).filter(Teacher.subject == ‘math‘).one() # print(lilei_q) # for i in lilei_q.students: # print(i.name) # xiaohong_q = sess.query(Student).filter(Student.name == ‘xiaohong‘).one() # lilei_q.students.remove(xiaohong_q) # # lilei_q.students.pop(1) # 以上两种方式删除的仅仅是关系 # sess.commit() # 删除记录 # hanmeimei_q = sess.query(Teacher).filter(Teacher.name == ‘hanmeimei‘).one() # print(hanmeimei_q) # sess.delete(hanmeimei_q) # 会把选中的记录及其相关关系都会删除，但是其关联的实体记录不受影响。即：只会删除教师表和关系表，学生表不受影响 # sess.commit() # lilei_q = sess.query(Teacher).filter(Teacher.name == ‘lilei‘).delete() # error 因为外键关系的存在，此种删除方式会报错 # sess.commit() # 级联删除 Teacher.relationship (后期)增加cascade=‘all,delete-orphan‘, single_parent=True 参数 # hanmeimei_q = sess.query(Teacher).filter_by(name=‘hanmeimei‘).one() # print(hanmeimei_q) # sess.delete(hanmeimei_q) # 此种方式删除，会将Teachers中选中记录删除，同时会因为级联原因删除学生记录以及关系记录，又因为删除了学生记录，所以又会把关系表中的相关记录都删掉 # sess.commit() # single_parent 意思是禁止多个记录与我建立关系 # order_by="TargeClass.col‘ 顺序排列 # order_by = ‘-Target.col‘ 逆序排列 # lilei_q = sess.query(Teacher).filter_by(name=‘lilei‘).one() # for i in lilei_q.students: # print(i.name+str(i.math))
第二种多对多
class TecStd(Base): __tablename__ = "tec_std_rel" tec_id = Column(Integer, ForeignKey("teachers.tid"), primary_key=True) # 需要把此表分别和Tec和Std两个结合着看,故需要两个primary_key std_id = Column(Integer, ForeignKey("students.sid"), primary_key=True) extra_data = Column(String(100)) teachers = relationship("Teacher", back_populates=‘students‘) # 此back_populates与 Teachers的bp相对应 students = relationship("Student", back_populates=‘teachers‘) # 此back_populates与Studentsde的bp相对应 class Teacher(Base): __tablename__ = "teachers" tid = Column(Integer, primary_key=True) name = Column(String(30)) subject = Column(String(10)) students = relationship("TecStd", # 和第三张表相关联 back_populates="teachers",cascade=‘all,delete-orphan‘) def __str__(self): return self.name class Student(Base): __tablename__ = "students" sid = Column(Integer, primary_key=True) name = Column(String(30)) teachers = relationship("TecStd", back_populates="students",cascade=‘all,delete-orphan‘) def __str__(self): return self.name # Base.metadata.drop_all(engine) Base.metadata.create_all(engine) lilei = Teacher(name=‘lilei‘, subject=‘math‘) hanmeimei = Teacher(name=‘hanmeimei‘, subject=‘chinese‘) xiaohong = Student(name=‘xiaohong‘) xiaoming = Student(name=‘xiaoming‘) xiaogang = Student(name=‘xiaogang‘) # lilei.students = [xiaohong, xiaoming, xiaogang] # error # hanmeimei.students = [xiaogang, xiaoming, xiaogang] # error # sess.add_all([lilei, hanmeimei]) # sess.commit() # 方法一 t_1 = TecStd(extra_data=‘ts‘) t_2 = TecStd(extra_data=‘ts‘) t_3 = TecStd(extra_data=‘ts‘) t_1_1 = TecStd(extra_data=‘ts‘) t_2_1 = TecStd(extra_data=‘ts‘) t_3_1 = TecStd(extra_data=‘ts‘) t_1.students = xiaoming t_2.students = xiaohong t_3.students = xiaogang t_1_1.students = xiaoming t_2_1.students = xiaohong t_3_1.students = xiaogang print(lilei.students) lilei.students.extend([t_1,t_2,t_3]) hanmeimei.students.extend([t_1_1, t_2_1,t_3_1]) # sess.add_all([lilei,hanmeimei]) # sess.commit() # # 方法二 # sess.add_all([lilei, hanmeimei, xiaohong, xiaoming, xiaogang]) # sess.commit() # li_1 = sess.query(Teacher).filter_by(name=‘lilei‘).one() # xiaogang_1 = sess.query(Student).filter_by(name=‘xiaogang‘).one() # xiaohong_1 = sess.query(Student).filter_by(name=‘xiaohong‘).one() # xiaoming_1 = sess.query(Student).filter_by(name=‘xiaoming‘).one() # t_1 = TecStd(tec_id=li_1.tid, std_id=xiaogang_1.sid, extra_data=‘lg‘) # t_2 = TecStd(tec_id=li_1.tid, std_id=xiaohong_1.sid, extra_data=‘lh‘) # t_3 = TecStd(tec_id=li_1.tid, std_id=xiaoming_1.sid, extra_data=‘lm‘) # sess.add_all([t_1, t_2, t_3]) # sess.commit() # 删除记录 # relationship 添加了级联删除标识,就可以删除teachers了，,同时关系表中的相关记录也会被删除,但依旧不会删除students中的记录 # lilei_q = sess.query(Teacher).filter_by(name=‘lilei‘).one() # sess.delete(lilei_q) # sess.commit() # xiaohong_q = sess.query(Student).filter_by(name=‘xiaohong‘).one() # print(xiaohong_q.teachers) # sess.delete(xiaohong_q) # sess.commit() # 删除关系 # 需要级联标删除识符 lilei_q = sess.query(Teacher).filter_by(name=‘lilei‘).one() # print(lilei_q.students) # for i in lilei_q.students: # print(i) # print(i.students.name) # lilei_q.students.pop() # sess.commit() # 需要级联标删除识符 # xiaohong_1 = sess.query(Student).filter_by(name=‘xiaohong‘).one() # r_1_q = sess.query(TecStd).filter(TecStd.tec_id == lilei_q.tid).filter(TecStd.std_id==xiaohong_1.sid).one() # print(r_1_q) # lilei_q.students.remove(r_1_q) # sess.commit() # 不需要级联标删除识符 # xiaohong_1 = sess.query(Student).filter_by(name=‘xiaohong‘).one() # r_1_q = sess.query(TecStd).filter(TecStd.tec_id == lilei_q.tid).filter(TecStd.std_id==xiaohong_1.sid).one() # print(r_1_q) # sess.delete(r_1_q) # sess.commit()