sqlalchemy外键的一些东西

Posted 2021-01-21 要一直走下去

 sqlalchemy中让mysql支持中文字符

engine = create_engine("mysql+pymysql://root:mysql8@localhost/mysqltest?charset=utf8", encoding=\'utf-8\')

数据库：

 

联表查询：

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)]
# 此处报错！！有外键关联的时候才能用，而且外键也需要用类映射出来。真TM麻烦！
result1 = session.query(Student).join(Study_record).all()
print(result1)

外键关联之双向反查：

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()

#   学员表student跟考勤表study_record是一对多的关系
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\'))
    # 双向反查关系，通过student字段可以看记录对应的学生，反过来通过my_study_record可看学生对应的记录
    student = relationship("Student", backref="my_study_record")
    def __repr__(self):   # self.student.name  这是它的牛逼之处：
        return "%s,%s,%s" %(self.day, self.status, self.student.name)

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

# 上面加了外键关联，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的上课记录咋查呢？在上面加一个双向反查关系
print(alex.my_study_record)  # [1,YES,alex, 2,NO,alex]

顾客表有两个外键，两个外键指向同一张表，此时的双向查询：

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()

# 顾客表Customer有两个外键，订单地址ID，邮寄地址ID。都关联了同一张表
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)

orms模块

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])
# 注意这里赋值的牛逼之处！！！直接用对象进行赋值
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()

init_data模块

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]

 

多对多映射。book表和author表，和book_author对应关系表。book和author形成多对多关系

建表模块orms

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

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

# 这个表不会手动管理。用户不操作它就不需要创建类，但是反查的时候需要关联这张表
book_to_author = Table("book_to_author", Base.metadata,
                       Column("id",Integer,primary_key=True),
                       Column("book_id",Integer,ForeignKey("book.id")),
                       Column("author_id",Integer,ForeignKey("author.id")))

class Author(Base):
    __tablename__="author"
    id = Column(Integer, primary_key=True)
    name = Column(String(32), nullable=False)

    books = relationship(\'Book\',secondary=book_to_author,backref=\'authors\')
    def __repr__(self):
        return "author_name:%s" %(self.name)
class Book(Base):
    __tablename__="book"
    id = Column(Integer, primary_key=True)
    name = Column(String(32), nullable=False)

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

Base.metadata.create_all(engine)

orms

插入数据模块init_data

from sqlalchemy.orm import sessionmaker
import orms

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

b1 = orms.Book(name="Book111")
b2 = orms.Book(name="Book222")
b3 = orms.Book(name="Book333")

a1 = orms.Author(name="Alex")
a2 = orms.Author(name="Jack")
a3 = orms.Author(name="Rain")

a1.books = [b1, b2]
a2.books = [b2, b3]
a3.books = [b1, b2, b3]

session.add_all([a1,a2,a3,b1,b2,b3])
session.commit()

init_data

查询，删除模块

from sqlalchemy.orm import sessionmaker
import orms

Session_class = sessionmaker(bind=orms.engine)
session = Session_class()
# 查询Alex的所有书
alex = session.query(orms.Author).filter(orms.Author.name=="Alex").first()
print(alex.books)  # [book_name:Book111, book_name:Book222]
# 查询book111的所有作者
book1 = session.query(orms.Book).filter(orms.Book.name=="book111").first()
print(book1.authors)  # [author_name:Alex, author_name:Rain]
# alex删除书book1
alex.books.remove(book1)
# 删除Alex作者
session.delete(alex)
session.commit()