Question

假设我们有一个基本模型。

class Log(models.Model):
    key = fields.BigInteger()
    calldate = fields.DateTimeField()
    followupdate = fields.DateTimeField()

可以为同一个键设置多个后续更新。我想要做的是在列表中出现最近（通过calldate）预定的后续行动。

在我看来，我有以下内容：

# views.py

def callbacks(request):
    """ get objects where a followupdate has been specified """
    q = Log.objects.filter(followupdate__isnull = False).order_by("-calldate")

    """ deduplicate key so only most recently scheduled followupdate show """ 
    newresults = []
    seen_key = []   
    for result in q:
        if result.key not in seen_key:
            seen_key.append(result.key)
            newresults.append(result)

    results = newresults
    """ What I want to do is equivalent to results.order_by("followupdate") """
    """ But since it's a dictionary now and not a queryset, I can't """
    return render_to_response('callbacks.html', {"callbacks":results})

我需要帮助的是通过密钥results重新排序字典followupdate。在每个字典中有一个这样的键：'followupdate': datetime.date(2013, 3, 25)这是我需要重新排序的。

Answer 1

.sort()似乎就是这样 -

l.sort(key=lambda item:item['followupdate'], reverse=True)

测试用例 -

>>> l = [{'followupdate': datetime.date(2013, 3, 25)}, {'followupdate': datetime.date(2013, 3, 24)}, {'followupdate': datetime.date(2013, 3, 29)}]
>>> l
[{'followupdate': datetime.date(2013, 3, 25)}, {'followupdate': datetime.date(2013, 3, 24)}, {'followupdate': datetime.date(2013, 3, 29)}]
>>> l.sort(key=lambda item:item['followupdate'], reverse=True)
>>> l
[{'followupdate': datetime.date(2013, 3, 29)}, {'followupdate': datetime.date(2013, 3, 25)}, {'followupdate': datetime.date(2013, 3, 24)}]

Answer 2

你应该让数据库进行重复数据删除，而不是从数据库中提取记录只是为了在Python中丢弃它们，这是浪费时间和带宽。

Django的对象关系映射不是这个，但你可以在SQL中这样做：

SELECT L1.*
FROM myapp_log AS L1,
     (SELECT MAX(date) AS maxdate, `key`
      FROM myapp_log GROUP BY `key`) as L2
WHERE L1.date = L2.maxdate
  AND L1.`key` = L2.`key`
  AND L1.followupdate IS NOT NULL
ORDER BY L1.date DESCENDING

（字段名称key需要引用，因为它是一个SQL关键字。）

然后，您可以使用raw() method从Django运行此查询，如下所示：

sql = '''
    SELECT L1.* FROM myapp_log AS L1,
    # and so on (see above)
    '''
q = Log.objects.raw(sql)

重复数据删除并重新排序字典

2 个答案: