Django 模型未更新

Question

我正在尝试计算用户访问页面的次数：

模型.py：

class Request(models.Model):
    user = models.ForeignKey(User)
    view = models.CharField(max_length = 250)
    visits = models.PositiveIntegerField()

视图.py

def daygaps(request,*a, **kw):

    request_counter = Request.objects.filter(
        user__username = request.user.username, view = 'daygaps')

    if request_counter:
        request_counter[0].visits += 1
        request_counter.update()

    else:
        Request.objects.create(
            user = request.user,
            visits = 1,
            view = 'daygaps')

当新用户第一次访问该页面时，“访问”设置为 = 1。随后的每次访问都应迭代计数。“else”块工作正常，但“visits”保持为 1，并且不会随着用户发出的每个新请求而改变。

我尝试过“.save()”方法，但是会引发错误，因为“request_counter”是一个查询集。

Answer 1

你可以这样做：

模型.py

class Request(models.Model):
    user = models.ForeignKey(User)
    view = models.CharField(max_length = 250)
    visits = models.PositiveIntegerField(default=0)

视图.py

def daygaps(request,*a, **kw):

    request_counter = Request.objects.get_or_create(
        user = request.user, view = 'daygaps')

    request_counter.visits += 1 # or =F('visits')+1 to avoid a race condition as suggested by Moses Koledoye
    request_counter.save()

或者

模型.py

class Request(models.Model):
    user = models.ForeignKey(User)
    view = models.CharField(max_length = 250)
    visits = models.PositiveIntegerField(default=1)

视图.py

def daygaps(request,*a, **kw):

    updated_count = Request.objects\
        .filter(user = request.user, view = 'daygaps')\
        .update(visits=F('visits')+1)

    if not updated_count:
        Request.objects.create(user = request.user, view = 'daygaps')

这也避免了竞争条件，并且具有不必检索对象的额外优点。

一般来说，如果更新足够简单，可以用F表达式来实现，我认为第二个更好。