django - 为什么 Django 不将我的 unique_together 约束强制为 form.ValidationError 而不是抛出异常？

Question

编辑:虽然这篇文章是 Django's ModelForm unique_together validation 的副本，这里接受的从 ModelForm 中删除“排除”的答案是比另一个问题中接受的答案更清晰的解决方案。

这是this question的后续.

如果我没有在 clean_title() 函数中明确检查 unique_together 约束，django 会抛出异常:

IntegrityError at /journal/journal/4

duplicate key value violates unique constraint "journal_journal_owner_id_key"

Request Method: POST

Request URL: http://localhost:8000/journal/journal/4

Exception Type: IntegrityError

Exception Value: duplicate key value violates unique constraint "journal_journal_owner_id_key"

Exception Location: /Library/Python/2.6/site-packages/django/db/backends/util.py in execute, line 19

然而，我的印象是 Django 会通过引发 ValidationError 很好地强制执行此约束，而不是我需要捕获的异常。

下面是我的代码，其中包含一个额外的 clean_title() 方法，我用作解决方法。但我想知道我做错了什么，以至于 django 没有以预期的方式强制执行约束。

谢谢。

型号代码:

class Journal (models.Model):
    owner = models.ForeignKey(User, related_name='journals')
    title = models.CharField(null=False, max_length=256)
    published = models.BooleanField(default=False)

    class Meta:
        unique_together = ("owner", "title")

    def __unicode__(self):
        return self.title 

表格代码:

class JournalForm (ModelForm):
    class Meta:
        model = models.Journal
        exclude = ('owner',)

    html_input = forms.CharField(label=u'Journal Content:', widget=TinyMCE(attrs={'cols':'85', 'rows':'40'}, ), )

    def clean_title(self):
        title = self.cleaned_data['title']
        if self.instance.id:
            if models.Journal.objects.filter(owner=self.instance.owner, title=title).exclude(id=self.instance.id).count() > 0:
               raise forms.ValidationError(u'You already have a Journal with that title. Please change your title so it is unique.')
        else:
            if models.Journal.objects.filter(owner=self.instance.owner, title=title).count() > 0:
               raise forms.ValidationError(u'You already have a Journal with that title. Please change your title so it is unique.')
        return title

查看代码:

def journal (request, id=''):
    if not request.user.is_active:
        return _handle_login(request)
    owner = request.user
    try:
        if request.method == 'GET':
            if '' == id:
                form = forms.JournalForm(instance=owner)
                return shortcuts.render_to_response('journal/Journal.html', { 'form':form, })
            journal = models.Journal.objects.get(id=id)
            if request.user.id != journal.owner.id:
                return http.HttpResponseForbidden('<h1>Access denied</h1>')
            data = {
                'title' : journal.title,
                'html_input' : _journal_fields_to_HTML(journal.id),
                'published' : journal.published
            }
            form = forms.JournalForm(data, instance=journal)
            return shortcuts.render_to_response('journal/Journal.html', { 'form':form, })
        elif request.method == 'POST':
            if LOGIN_FORM_KEY in request.POST:
                return _handle_login(request)
            else:
                if '' == id:
                    journal = models.Journal()
                    journal.owner = owner
                else:
                    journal = models.Journal.objects.get(id=id)
                form = forms.JournalForm(data=request.POST, instance=journal)
                if form.is_valid():
                    journal.owner = owner
                    journal.title = form.cleaned_data['title']
                    journal.published = form.cleaned_data['published']
                    journal.save()
                    if _HTML_to_journal_fields(journal, form.cleaned_data['html_input']):
                        html_memo = "Save successful."
                    else:
                        html_memo = "Unable to save Journal."
                    return shortcuts.render_to_response('journal/Journal.html', { 'form':form, 'saved':html_memo})
                else:
                    return shortcuts.render_to_response('journal/Journal.html', { 'form':form })
        return http.HttpResponseNotAllowed(['GET', 'POST'])
    except models.Journal.DoesNotExist:
        return http.HttpResponseNotFound('<h1>Requested journal not found</h1>')

更新工作代码:
感谢丹尼尔罗斯曼。

型号代码与上述相同。

表单代码 - 删除 exclude 语句和 clean_title 函数:

class JournalForm (ModelForm):
    class Meta:
        model = models.Journal

    html_input = forms.CharField(label=u'Journal Content:', widget=TinyMCE(attrs={'cols':'85', 'rows':'40'},),)

查看代码 - 添加自定义唯一性错误消息:

def journal (request, id=''):
    if not request.user.is_active:
        return _handle_login(request)
    try:
        if '' != id:
            journal = models.Journal.objects.get(id=id)
            if request.user.id != journal.owner.id:
                return http.HttpResponseForbidden('<h1>Access denied</h1>')
        if request.method == 'GET':
            if '' == id:
                form = forms.JournalForm()
            else:
                form = forms.JournalForm(initial={'html_input':_journal_fields_to_HTML(journal.id)},instance=journal)
            return shortcuts.render_to_response('journal/Journal.html', { 'form':form, })
        elif request.method == 'POST':
            if LOGIN_FORM_KEY in request.POST:
                return _handle_login(request)
            data = request.POST.copy()
            data['owner'] = request.user.id
            if '' == id:
                form = forms.JournalForm(data)
            else:
                form = forms.JournalForm(data, instance=journal)
            if form.is_valid():
                journal = form.save()
                if _HTML_to_journal_fields(journal, form.cleaned_data['html_input']):
                    html_memo = "Save successful."
                else:
                    html_memo = "Unable to save Journal."
                return shortcuts.render_to_response('journal/Journal.html', { 'form':form, 'saved':html_memo})
            else:
                if form.unique_error_message:
                    err_message = u'You already have a Lab Journal with that title. Please change your title so it is unique.'
                else:
                    err_message = form.errors
                return shortcuts.render_to_response('journal/Journal.html', { 'form':form, 'error_message':err_message})
        return http.HttpResponseNotAllowed(['GET', 'POST'])
    except models.Journal.DoesNotExist:
        return http.HttpResponseNotFound('<h1>Requested journal not found</h1>')

Answer 1

问题是您专门排除了唯一检查中涉及的字段之一，并且在这种情况下 Django 不会运行检查 - 请参阅 _get_unique_checks django.db.models.base 的第 722 行中的方法.

而不是排除 owner字段，我会考虑将它从模板中删除，并在您在实例化时传入的数据上显式设置值:

 data = request.POST.copy()
 data['owner'] = request.user.id
 form = JournalForm(data, instance=journal)

请注意，您在这里并没有真正使用 modelform 的强大功能。您不需要在初始 GET 上显式设置数据字典 - 事实上，您不应该传递 data参数，因为它会触发验证:如果您需要传入与实例不同的值，您应该使用 initial反而。但大多数时候，只是路过 instance足够。

而且，在 POST 上，您也不需要明确设置值:您可以这样做:

journal = form.save()

这将正确更新实例并返回它。