SQLAlchemy ORM - 應用過濾器

在本章中，我們將討論如何應用過濾器，以及某些過濾器操作及其程式碼。

使用 filter() 方法可以對 Query 物件表示的結果集施加某些條件。filter 方法的一般用法如下 −

session.query(class).filter(criteria)

在以下示例中，透過條件 (ID>2) 篩選了 SELECT 查詢對 Customers 表獲得的結果集 −

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

此語句將轉換為以下 SQL 表示式 −

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 > ?

由於已將繫結引數 (?) 賦予 2，因此只會顯示 ID 列>2 的行。完整程式碼如下 −

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 控制檯中顯示的輸出如下 −

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