如何在Django中查询/过滤M2M 'through'对象

Question

我有一个基本的模型……

  class Campaign(models.Model):
    name = models.CharField(_('name'), max_length=80, unique=True)
    recipients = models.ManyToManyField('Person', blank=True, null=True, through='Recipient')


  class Recipient(models.Model):
    campaign = models.ForeignKey(Campaign)
    person = models.ForeignKey('Person')


  class Person(models.Model):
    first_name = models.CharField(_('first name'), max_length=30, blank=True)
    last_name = models.CharField(_('last name'), max_length=30, blank=True)

我想要一个查询，能够找到所有不在特定活动中的Person对象。

如果能像这样简单就好了：

Person.objects.all().exclude(<mycampaign>.recipients.all())

但我们知道这样是不行的。

更具体一点，我想在一个表单类中实现这个功能，Q对象的用法看起来是对的，但我就是搞不定……这是我的表单：

class RecipientsForm(forms.Form):
  def __init__(self, campaign, *args, **kwargs): 
    self.campaign = campaign
    self.helper = FormHelper()
    self.helper.add_input(Submit('submit','Add',css_class='primaryAction'))
    self.helper.layout = Layout(
        Fieldset(
          '',
          'recipients',
          css_class='inlineLabels')
      )
    return super(RecipientsForm, self).__init__(*args, **kwargs)

  recipients = forms.ModelMultipleChoiceField(
  # old queryset queryset=Person.objects.all(),
                 queryset=Person.objects.filter(~Q(id__in=self.campaign.recipients.all())),
                 widget=forms.widgets.CheckboxSelectMultiple,
                 label="Add Recipients",
                 required=True,)

  def save(self, force_insert=False, force_update=False, commit=True):
    recipients = self.cleaned_data['recipients']
    for person in recipients:
      recipient = Recipient(campaign=self.campaign,person=person)
      recipient.save()

Answer 1

我觉得这样就可以了。

from django.db.models import Q
Person.objects.filter(~Q(id__in=<mycampaign>.recipients.all())

Answer 2

这是答案……问题在于我的表单是针对收件人对象，而不是活动对象……Furbeenator的回答是朝着正确方向迈出的一步……还有一些来自django IRC的帮助。

class RecipientsForm(forms.ModelForm):

  def __init__(self, *args, **kwargs):
    self.campaign = kwargs.pop('campaign', None)
    super(RecipientsForm, self).__init__(*args, **kwargs)

    if self.instance and self.campaign:
      self.fields['recipients'] = forms.ModelMultipleChoiceField(
        queryset=Person.objects.filter(~Q(id__in=self.campaign.recipients.all())),
        widget=forms.widgets.CheckboxSelectMultiple,
        label='Recipients', help_text='Pick the recipients to add to the campaign',
        required=False,
      )
    elif self.campaign:
      self.fields['recipients'] = forms.ModelMultipleChoiceField(
        queryset=Person.objects.filter(~Q(id__in=self.campaign.recipients.all())),
        widget=forms.widgets.CheckboxSelectMultiple,
        label='Recipients', help_text='Pick the recipients to add to the campaign',
        required=False,
      )
    else:
      pass

  def save(self, force_insert=False, force_update=False, commit=True):
    recipients = self.cleaned_data['recipients']
    for person in recipients:
      recipient = Recipient(campaign=self.campaign,person=person)
      recipient.save()

  class Meta:
    model = Campaign
    fields = ['recipients',]