如何从其他模型函数做模型查询？

Question

我有以下类：学生，LabJournal，JournalResponse和JournalField。我想为学生定义一个“状态”功能，以确定他们已经回答了多少个问题（JournalField）（JournalResponse）。问题是功能死亡，没有对下面的行返回：

total_questions = models.JournalResponse.objects.filter(owner__exact=self.id).filter(field__journal__exact=self.assignment).count() 

我的猜测是，我做的模型查询错误从类定义之内，或者说不允许你从内查询一个单独的模型。不过，我没有在文档中找到任何证实或否认这一点的内容，并且没有任何错误，因此很难进行调试。运行Django 1.1。下面

代码：

class Student (models.Model): 
    user = models.ForeignKey(User, unique=True, null=False, related_name='student') 
    teacher = models.ForeignKey(User, null=False, related_name='students') 
    assignment = models.ForeignKey(LabJournal, blank=True, null=True, related_name='students') 

    def get_absolute_url(self): 
     return "/labjournal/student/%i/" % self.id 

    def status(self): 
     if self.assignment == None : return "unassigned" 
     percent_done = 0 
     total_questions = models.JournalResponse.objects.filter(owner__exact=self.id).filter(field__journal__exact=self.assignment).count() 
     answered_questions = models.JournalResponse.objects.filter(owner__exact=self.id).filter(field__journal__exact=self.assignment).filter(text!=None).count() 
     percent_done = (answered_questions/total_questions)*100 
     return '%d%% done' % percent_done 

class JournalResponse (models.Model): 
    owner = models.ForeignKey(Student, null=False, related_name='responses') 
    field = models.ForeignKey(JournalField, null=False, related_name='responses') 
    text = models.TextField(null=True, blank=True) 
    file = models.URLField(null=True, blank=True) 


class JournalField (models.Model): 
    TYPE_CHOICES = (
     (u'HTML', u'HTML'), 
     (u'IF', u'ImageField'), 
     (u'TF', u'TextField'), 
    ) 

    journal = models.ForeignKey(LabJournal, null=False, related_name='fields', help_text='Parent Journal') 
    ordinal = models.IntegerField(help_text='Field order') 
    type = models.CharField(null=False, max_length=64, choices=TYPE_CHOICES, help_text='Field type') 
    # Contains HTML content for HTML fields, contains the text marked "question" closest 
    # to and above the current field for picture and text entry fields 
    content = models.TextField(help_text='Should contain HTML content for HTML (question) fields or associated (previous question) HTML for ImageFields and TextFields.') 

修订 这里的工作状态的方法：（？AttributeError的）

def status(self): 
    if self.assignment == None : return "unassigned" 
    percent_done = 0 
    # sets up query, but doesn't actually hit database 
    response_set = self.responses.filter(owner=self).filter(field__journal=self.assignment) 
    # force float so divide returns float 
    # the two count statements are the only two actual hits on the database 
    total_questions = float(response_set.count()) 
    answered_questions = float(response_set.exclude(text='').count()) 
    percent_done = (answered_questions/total_questions)*100 
    return '%d%% done' % percent_done 

Answer 1

它看起来像你指的是哪个models.JournalResponse不应该存在，因为在班级定义中相同models的名字是指django.db.models

您需要通过实际的模型对象来引用它，所以JournalResponse.objects.filter()。

你的情况，你必须JournalResponse从Student反向关系，所以你可以简单地使用self.journalresponse_set.filter()访问JournalResponse.objects.filter(student=self) http://docs.djangoproject.com/en/dev/topics/db/queries/#following-relationships-backward

尝试：

self.journalresponse_set.filter(field__journal=self.assignment) 

另外，你的下一个过滤器行将为打破以及text!=None。改为使用exclude(text=None)语法。