在Django的视图中使用数据库查询的方法
在视图中也有笨方法可以从数据库中获取数据。 很简单: 用现有的任何 Python 类库执行一条 SQL 查询并对结果进行一些处理。
在本例的视图中,我们使用了 MySQLdb 类库(可以从 http://www.djangoproject.com/r/python-mysql/ 获得)来连接 MySQL 数据库,取回一些记录,将它们提供给模板以显示一个网页:
from django.shortcuts import render_to_response import MySQLdb def book_list(request): db = MySQLdb.connect(user='me', db='mydb', passwd='secret', host='localhost') cursor = db.cursor() cursor.execute('SELECT name FROM books ORDER BY name') names = [row[0] for row in cursor.fetchall()] db.close() return render_to_response('book_list.html', {'names': names})
这个方法可用,但很快一些问题将出现在你面前:
我们将数据库连接参数硬行编码于代码之中。 理想情况下,这些参数应当保存在 Django 配置中。
我们不得不重复同样的代码: 创建数据库连接、创建数据库游标、执行某个语句、然后关闭数据库。 理想情况下,我们所需要应该只是指定所需的结果。
它把我们栓死在 MySQL 之上。 如果过段时间,我们要从 MySQL 换到 PostgreSQL,就不得不使用不同的数据库适配器(例如 psycopg 而不是 MySQLdb ),改变连接参数,根据 SQL 语句的类型可能还要修改SQL 。 理想情况下,应对所使用的数据库服务器进行抽象,这样一来只在一处修改即可变换数据库服务器。 (如果你正在建立一个开源的Django应用程序来尽可能让更多人使用的话,这个特性是非常适当的。)
正如你所期待的,Django数据库层正是致力于解决这些问题。 以下提前揭示了如何使用 Django 数据库 API 重写之前那个视图。
from django.shortcuts import render_to_response from mysite.books.models import Book def book_list(request): books = Book.objects.order_by('name') return render_to_response('book_list.html', {'books': books})
我们将在本章稍后的地方解释这段代码。 目前而言,仅需对它有个大致的认识。

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