如何在表格中对Django元素的列进行排序？
我该怎么给一个表格里的Django元素排序呢？
我发现Django的管理后台可以做到这一点。那是怎么实现的呢？
有没有什么网站资源可以让我了解一下这个？
*这里提到的“Django元素”是指那些可以插入的模板对象，长得像这样：
{{ x.y }}
3 个回答
1
我创建了这个工具类，是因为我看到了管理员在Django 0.96版本中是怎么做的。
这个工具类可以根据GET请求中的参数来处理排序的标准，并提供一些变量，这些变量可以用来生成表头的排序链接。这些链接会遵循当前的排序字段和方向，如果同一个表头再次被点击，排序方向会反转。
ORDER_VAR = 'o'
ORDER_TYPE_VAR = 'ot'
class SortHeaders:
"""
Handles generation of an argument for the Django ORM's
``order_by`` method and generation of table headers which reflect
the currently selected sort, based on defined table headers with
matching sort criteria.
Based in part on the Django Admin application's ``ChangeList``
functionality.
"""
def __init__(self, request, headers, default_order_field=None,
default_order_type='asc', additional_params=None):
"""
request
The request currently being processed - the current sort
order field and type are determined based on GET
parameters.
headers
A list of two-tuples of header text and matching ordering
criteria for use with the Django ORM's ``order_by``
method. A criterion of ``None`` indicates that a header
is not sortable.
default_order_field
The index of the header definition to be used for default
ordering and when an invalid or non-sortable header is
specified in GET parameters. If not specified, the index
of the first sortable header will be used.
default_order_type
The default type of ordering used - must be one of
``'asc`` or ``'desc'``.
additional_params:
Query parameters which should always appear in sort links,
specified as a dictionary mapping parameter names to
values. For example, this might contain the current page
number if you're sorting a paginated list of items.
"""
if default_order_field is None:
for i, (header, query_lookup) in enumerate(headers):
if query_lookup is not None:
default_order_field = i
break
if default_order_field is None:
raise AttributeError('No default_order_field was specified and none of the header definitions given were sortable.')
if default_order_type not in ('asc', 'desc'):
raise AttributeError('If given, default_order_type must be one of \'asc\' or \'desc\'.')
if additional_params is None: additional_params = {}
self.header_defs = headers
self.additional_params = additional_params
self.order_field, self.order_type = default_order_field, default_order_type
# Determine order field and order type for the current request
params = dict(request.GET.items())
if ORDER_VAR in params:
try:
new_order_field = int(params[ORDER_VAR])
if headers[new_order_field][1] is not None:
self.order_field = new_order_field
except (IndexError, ValueError):
pass # Use the default
if ORDER_TYPE_VAR in params and params[ORDER_TYPE_VAR] in ('asc', 'desc'):
self.order_type = params[ORDER_TYPE_VAR]
def headers(self):
"""
Generates dicts containing header and sort link details for
all defined headers.
"""
for i, (header, order_criterion) in enumerate(self.header_defs):
th_classes = []
new_order_type = 'asc'
if i == self.order_field:
th_classes.append('sorted %sending' % self.order_type)
new_order_type = {'asc': 'desc', 'desc': 'asc'}[self.order_type]
yield {
'text': header,
'sortable': order_criterion is not None,
'url': self.get_query_string({ORDER_VAR: i, ORDER_TYPE_VAR: new_order_type}),
'class_attr': (th_classes and ' class="%s"' % ' '.join(th_classes) or ''),
}
def get_query_string(self, params):
"""
Creates a query string from the given dictionary of
parameters, including any additonal parameters which should
always be present.
"""
params.update(self.additional_params)
return '?%s' % '&'.join(['%s=%s' % (param, value) \
for param, value in params.items()])
def get_order_by(self):
"""
Creates an ordering criterion based on the current order
field and order type, for use with the Django ORM's
``order_by`` method.
"""
return '%s%s' % (
self.order_type == 'desc' and '-' or '',
self.header_defs[self.order_field][1],
)
示例视图：
from somewhere import SortHeaders
from django.contrib.auth.models import User
from django.shortcuts import render_to_response
LIST_HEADERS = (
('Username', 'username'),
('First Name', 'first_name'),
('Last Name', 'last_name'),
('Email', None),
)
def user_list(request):
sort_headers = SortHeaders(request, LIST_HEADERS)
users = User.objects.order_by(sort_headers.get_order_by())
return render_to_response('users/user_list.html', {
'users': users,
'headers': list(sort_headers.headers()),
})
示例模板（users/user_list.html）：
{% load my_tags %}
<table cellspacing="0">
<thead>
<tr>
{% table_header headers %}
</tr>
</thead>
<tbody>
{% for user in users %}<tr class="{% cycle odd,even %}">
<td><a href="{{ user.get_absolute_url }}">{{ user.username }}</a></td>
<td>{{ user.first_name }}</td>
<td>{{ user.last_name }}</td>
<td>{{ user.email }}</td>
</tr>
{% endfor %}
</tbody>
</table>
示例包含标签（templatetags/my_tags.py）：
from django import template
def table_header(context, headers):
return {
'headers': headers,
}
register = template.Library()
register.inclusion_tag('table_header.html', takes_context=True)(table_header)
示例包含标签模板（table_header.html）：
{% for header in headers %}<th{{ header.class_attr }}>
{% if header.sortable %}<a href="{{ header.url }}">{% endif %}
{{ header.text }}
{% if header.sortable %}</a>{% endif %}
</th>{% endfor %}
3
值得看看Django管理后台中ChangeList的源代码：
http://code.djangoproject.com/svn/django/branches/releases/1.2.X/django/contrib/admin/views/main.py
排序的过程大致是这样的：
你在管理后台点击某一列的标题，这时页面会重新加载，并在网址中带上相关的排序参数，这个参数可以在request.GET中找到。
这个排序参数会在ChangeList视图中被解析：
self.order_field, self.order_type = self.get_ordering()
接下来会生成查询集：
self.query_set = self.get_query_set()。具体来说，函数中的以下几行代码：
if self.order_field: qs = qs.order_by('%s%s' % ((self.order_type == 'desc' and '-' or ''), self.order_field))
我认为，使用Django管理后台的同时理解源代码是学习Django的最佳方式之一！
1
如果你是通过查询获取数据的，那就可以在视图里使用 order_by() 方法。如果你是处理一个列表，那就可以在视图里使用 sort() 方法。