处理相关对象 - 芒果文档

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📜 处理相关对象

📅 最后修改于: 2020-11-27 07:51:07 🧑 作者: Mango

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，一个空白的发票集合将以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属性将为空列表。我们可以将列表中的项目分配为-

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)

现在让我们在SQLiteStudio的表格视图中查看客户表格和发票表格的内容-

客户表视图

发票表

您可以通过使用以下命令在构造函数本身中提供发票的映射属性来构造Customer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()函数添加的对象列表，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()