SQLAlchemy ORM - 应用过滤器

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在本章中，我们将讨论如何应用过滤器以及某些过滤器操作及其代码。

查询对象表示的结果集可以通过使用filter()方法满足某些条件。过滤方法的一般用法如下 -

session.query(class).filter(criteria)

在以下示例中，通过对 Customers 表进行 SELECT 查询获得的结果集按条件 (ID>2) 进行过滤 -

result = session.query(Customers).filter(Customers.id>2)

该语句将转换为以下 SQL 表达式 -

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE customers.id > ?

由于绑定参数 (?) 指定为 2，因此仅显示 ID 列>2 的行。完整的代码如下 -

from sqlalchemy import Column, Integer, String
from sqlalchemy import create_engine
engine = create_engine('sqlite:///sales.db', echo = True)
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class Customers(Base):
   __tablename__ = 'customers'
   
   id = Column(Integer, primary_key = True)
   name = Column(String)

   address = Column(String)
   email = Column(String)

from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind = engine)
session = Session()
result = session.query(Customers).filter(Customers.id>2)

for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

Python 控制台中显示的输出如下 -

ID: 3 Name: Rajender Nath Address: Sector 40, Gurgaon Email: nath@gmail.com
ID: 4 Name: S.M.Krishna Address: Budhwar Peth, Pune Email: smk@gmail.com