使用相关对象

在本章中，我们将重点介绍 SQLAlchemy ORM 中的相关对象。

现在，当我们创建一个 Customer 对象时，一个空白的invoices集合将以 Python 列表的形式出现。

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

c1.invoices 的invoices属性将是一个空列表。我们可以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 Session 对象将此对象提交到数据库，如下所示 −

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

这将自动为客户和invoices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)

现在让我们在 SQLiteStudio 的表视图中查看客户表和invoices表的内容 −

您可以使用以下命令在构造函数本身中提供invoices的映射属性来构造客户对象−

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

或者使用会话对象的 add_all() 函数添加对象列表，如下所示 −

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()