SQLAlchemy 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。 filter方法的一般用法如下-
session.query(class).filter(criteria)
在下面的例子中，通过对Customers表的SELECT查询得到的结果集被一个条件过滤，(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
