Django中MultiSelectField默认值设置及邮件偏好判断

1. 设置email_preferences默认选中所有选项 #

修改Account模型中的email_preferences字段，添加default参数，值为所有偏好选项的value组成的列表：

class Account(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    joined_groups = models.ManyToManyField(Group, related_name='joined_group', blank=True)
    created_groups = models.ManyToManyField(Group, blank=True)
    EMAIL_PREFERENCES = [
        ('user_emails', 'User Emails'),
        ('group_emails', 'Group Emails'),
        ('leader_emails', 'Leader Emails'),
    ]
    email_preferences = MultiSelectField(
        verbose_name = 'Email Preferences',
        choices=EMAIL_PREFERENCES,
        blank=True,
        max_choices=3,
        max_length=255,
        # 添加默认值，选中所有选项
        default=['user_emails', 'group_emails', 'leader_emails']
    )

新用户注册时，创建的Account实例会自动默认选中所有邮件偏好。若需处理已存在的用户数据，可通过数据迁移或后台批量更新完成默认值设置。

2. 在视图中判断是否发送邮件通知 #

在CreateGroup的form_valid方法中，先将用户的email_preferences分割为列表，再判断'leader_emails'是否在列表中，满足条件才触发邮件任务：

class CreateGroup(CreateView):
    model = Group
    form_class = GroupForm
    template_name = 'create_group.html'

    def form_valid(self, form):
        group = form.save()
        group.joined.add(self.request.user)
        account = self.request.user.account
        account.created_chaburahs.add(group)
        account.joined_chaburahs.add(group)
        email = account.user.email

        # 判断用户是否开启Leader Emails偏好
        preferences = account.email_preferences.split(',') if account.email_preferences else []
        if 'leader_emails' in preferences:
            # celery task to send email
            create_group_notification_task.delay(email)
        
        return HttpResponseRedirect(reverse('group_detail', args=[str(group.pk)]))

如果使用的是django-multiselectfield库，该字段会自动将存储的字符串转为列表，此时可直接用if 'leader_emails' in account.email_preferences:判断，无需手动分割。

内容的提问来源于stack exchange，提问作者Yehuda