SQLAlchemy ORM – 应用过滤器

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。

Query 对象表示的结果集可以通过使用 filter() 方法服从某些条件。过滤方法的一般用法如下 –

session.query(class).filter(criteria)

在以下示例中，通过对客户表的 SELECT 查询获得的结果集按条件过滤，(ID>2) –

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

此语句将转换为以下 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 (?) 为 2，因此只会显示 ID column>2 的那些行。完整代码如下 –

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