python - Django:检查存在哪个相关对象

Question

我有两个引用 django User 的不同模型，即 Recruiter 和 Userprofile。

我有一个接收 User 对象作为参数的函数。我需要检查存在哪些相关对象并采取相应的措施。我正在使用嵌套的 try-catch 来执行此操作:

def some_function(user, ....):
    ...
    try:
        profile = user.userprofile
        profile.profile_pic.save('{0}_social.jpg'.format(user.username))
        profile.save()
    except:
        try:
            recruiter = user.recruiter
            recruiter.cover_pic.save('{0}_social.jpg'.format(user.username))
            recruiter.save()
        except:
            pass

是否有更好/更优雅的方式来做到这一点？

编辑:正在考虑的模型如下

class Recruiter(models.Model):
    user = models.OneToOneField(User, unique=True, related_name='recruiter')
    ...

class UserProfile(models.Model):
    user = models.OneToOneField(User, unique=True, related_name='userprofile')
    ...

Answer 1

您可以使用 .exists() QuerySet API，就像这样(假设 user 是 User 模型的一个实例，并且 Userprofile 和 Recruiter 键是该模型的一个字段也命名为 用户):

def some_function(user, ...):
    if Userprofile.objects.filter(user=user).exists()
        profile = user.userprofile
        profile.profile_pic.save('{0}_social.jpg'.format(user.username))
        profile.save()
    elif Recruiter.objects.filter(user=user).exists()
        recruiter = user.recruiter
        recruiter.cover_pic.save('{0}_social.jpg'.format(user.username))
        recruiter.save()
    else:
        # User has neither Userprofile nor Recruiter associated with it!
        # Do something here to handle that case, or just get rid of the else

请注意，.exists() 调用将首先查询对象是否存在，然后是访问该对象的行(例如，user.userprofile) 将运行另一个查询以实际访问该对象。一种稍微优化的方式可能是:

def some_function(user, ...):
    userprofiles = Userprofile.objects.filter(user=user)
    recruiters = Recruiter.objects.filter(user=user)
    if len(userprofiles):
        profile = userprofiles[0]
        profile.profile_pic.save('{0}_social.jpg'.format(user.username))
        profile.save()
    elif len(recruiters):
        recruiter = recruiters[0]
        recruiter.cover_pic.save('{0}_social.jpg'.format(user.username))
        recruiter.save()
    else:
        # User has neither Userprofile nor Recruiter associated with it!
        # Do something here to handle that case, or just get rid of the else