Python的Django框架中的表单处理示例
组建一个关于书籍、作者、出版社的例子：
from django.db import models class Publisher(models.Model): name = models.CharField(max_length=30) address = models.CharField(max_length=50) city = models.CharField(max_length=60) state_province = models.CharField(max_length=30) country = models.CharField(max_length=50) website = models.URLField() class Author(models.Model): first_name = models.CharField(max_length=30) last_name = models.CharField(max_length=40) email = models.EmailField() class Book(models.Model): title = models.CharField(max_length=100) authors = models.ManyToManyField(Author) publisher = models.ForeignKey(Publisher) publication_date = models.DateField()
我们现在来创建一个简单的view函数以便让用户可以通过书名从数据库中查找书籍。
通常，表单开发分为两个部分： 前端HTML页面用户接口和后台view函数对所提交数据的处理过程。 第一部分很简单；现在我们来建立个view来显示一个搜索表单：
from django.shortcuts import render_to_response
def search_form(request):
return render_to_response('search_form.html')
这个view函数可以放到Python的搜索路径的任何位置。 为了便于讨论，咱们将它放在 books/views.py 里。
这个 search_form.html 模板，可能看起来是这样的：
<html>
<head>
<title>Search</title>
</head>
<body>
<form action="/search/" method="get">
<input type="text" name="q">
<input type="submit" value="Search">
</form>
</body>
</html>
而 urls.py 中的 URLpattern 可能是这样的：
from mysite.books import views
urlpatterns = patterns('',
# ...
(r'^search-form/$', views.search_form),
# ...
)
（注意，我们直接将views模块import进来了，而不是用类似 from mysite.views import search_form 这样的语句，因为前者看起来更简洁。）
现在，如果你运行 runserver 命令，然后访问http://127.0.0.1:8000/search-form/，你会看到搜索界面。 非常简单。
不过，当你通过这个form提交数据时，你会得到一个Django 404错误。 这个Form指向的URL /search/ 还没有被实现。 让我们添加第二个视图函数并设置URL：
# urls.py
urlpatterns = patterns('',
# ...
(r'^search-form/$', views.search_form),
(r'^search/$', views.search),
# ...
)
# views.py
def search(request):
if 'q' in request.GET:
message = 'You searched for: %r' % request.GET['q']
else:
message = 'You submitted an empty form.'
return HttpResponse(message)
暂时先只显示用户搜索的字词，以确定搜索数据被正确地提交给了Django，这样你就会知道搜索数据是如何在这个系统中传递的。 简而言之：
在HTML里我们定义了一个变量q。当提交表单时，变量q的值通过GET(method=”get”)附加在URL /search/上。
处理/search/（search()）的视图通过request.GET来获取q的值。
需要注意的是在这里明确地判断q是否包含在request.GET中。就像上面request.META小节里面提到，对于用户提交过来的数据，甚至是正确的数据，都需要进行过滤。 在这里若没有进行检测，那么用户提交一个空的表单将引发KeyError异常：
# BAD! def bad_search(request): # The following line will raise KeyError if 'q' hasn't # been submitted! message = 'You searched for: %r' % request.GET['q'] return HttpResponse(message)
查询字符串参数
因为使用GET方法的数据是通过查询字符串的方式传递的（例如/search/?q=django），所以我们可以使用requet.GET来获取这些数据。我们知道在视图里可以使用request.GET来获取传统URL里的查询字符串（例如hours=3）。
获取使用POST方法的数据与GET的相似，只是使用request.POST代替了request.GET。那么，POST与GET之间有什么不同？当我们提交表单仅仅需要获取数据时就可以用GET； 而当我们提交表单时需要更改服务器数据的状态，或者说发送e-mail，或者其他不仅仅是获取并显示数据的时候就使用POST。 在这个搜索书籍的例子里，我们使用GET，因为这个查询不会更改服务器数据的状态。 (如果你有兴趣了解更多关于GET和POST的知识，可以参见http://www.w3.org/2001/tag/doc/whenToUseGet.html。)
既然已经确认用户所提交的数据是有效的，那么接下来就可以从数据库中查询这个有效的数据（同样，在views.py里操作）：
from django.http import HttpResponse
from django.shortcuts import render_to_response
from mysite.books.models import Book
def search(request):
if 'q' in request.GET and request.GET['q']:
q = request.GET['q']
books = Book.objects.filter(title__icontains=q)
return render_to_response('search_results.html',
{'books': books, 'query': q})
else:
return HttpResponse('Please submit a search term.')
让我们来分析一下上面的代码：
- 除了检查q是否存在于request.GET之外，我们还检查来reuqest.GET[‘q']的值是否为空。
- 我们使用Book.objects.filter(title__icontains=q)获取数据库中标题包含q的书籍。 icontains是一个查询关键字。这个语句可以理解为获取标题里包含q的书籍，不区分大小写。
- 这是实现书籍查询的一个很简单的方法。 我们不推荐在一个包含大量产品的数据库中使用icontains查询，因为那会很慢。 （在真实的案例中，我们可以使用以某种分类的自定义查询系统。 在网上搜索“开源 全文搜索”看看是否有好的方法）
最后，我们给模板传递来books，一个包含Book对象的列表。 查询结果的显示模板search_results.html如下所示：
<p>You searched for: <strong>{{ query }}</strong></p>
{% if books %}
<p>Found {{ books|length }} book{{ books|pluralize }}.</p>
<ul>
{% for book in books %}
<li>{{ book.title }}</li>
{% endfor %}
</ul>
{% else %}
<p>No books matched your search criteria.</p>
{% endif %}
注意这里pluralize的使用，这个过滤器在适当的时候会输出s（例如找到多本书籍）。
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