Sqlalchemy 简明教程

Working with Related Objects

在本章中，我们将重点关注 SQLAlchemy ORM 中的相关对象。

现在，当我们创建一个客户对象时，Python 列表的形式将出现一个空白的账单集合。

c1 = Customer(name = "Gopal Krishna", address = "Bank Street Hydarebad", email = "gk@gmail.com")

c1.invoices 的 invoices 特性将是一个空列表。我们可将列表中的项目指定为 -

c1.invoices = [Invoice(invno = 10, amount = 15000), Invoice(invno = 14, amount = 3850)]

让我们使用如下 Session 对象将此对象提交到数据库 -

from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind = engine)
session = Session()
session.add(c1)
session.commit()

这将自动为客户和发票表生成 INSERT 查询 -

INSERT INTO customers (name, address, email) VALUES (?, ?, ?)
('Gopal Krishna', 'Bank Street Hydarebad', 'gk@gmail.com')
INSERT INTO invoices (custid, invno, amount) VALUES (?, ?, ?)
(2, 10, 15000)
INSERT INTO invoices (custid, invno, amount) VALUES (?, ?, ?)
(2, 14, 3850)

让我们现在在 SQLiteStudio 表视图中查看客户表和发票表的内容 -

customers table view
invoices table

您可通过使用下列命令，在构造函数中为发票提供映射的特性，来构造客户对象 -

c2 = [
   Customer(
      name = "Govind Pant",
      address = "Gulmandi Aurangabad",
      email = "gpant@gmail.com",
      invoices = [Invoice(invno = 3, amount = 10000),
      Invoice(invno = 4, amount = 5000)]
   )
]

或一组待使用 add_all() 函数（如以下所示）添加的对象 -

rows = [
   Customer(
      name = "Govind Kala",
      address = "Gulmandi Aurangabad",
      email = "kala@gmail.com",
      invoices = [Invoice(invno = 7, amount = 12000), Invoice(invno = 8, amount = 18500)]),

   Customer(
      name = "Abdul Rahman",
      address = "Rohtak",
      email = "abdulr@gmail.com",
      invoices = [Invoice(invno = 9, amount = 15000),
      Invoice(invno = 11, amount = 6000)
   ])
]

session.add_all(rows)
session.commit()