Django模型過濾器，取決於關係

Question

我怎麼能只有至少有一個「職位」相關的類別??，希望它是有道理的！？

**models.py** 
class Category(models.Model): 
    name = models.CharField(max_length=50) 

def __unicode__(self): 
    return self.name 

class Post(models.Model): 
    name = models.CharField(max_length=50) 
    categories = models.ManyToManyField(Category) 

    def __unicode__(self): 
     return self.name 

**view.py:** 
def index(request): 
    categories = category.objects.filter(???) 

我只有在有至少一個「郵報」的相關??，類別怎能希望這是有道理的！？

Answer 1

categories = Category.objects.exclude(post=None) 

Answer 2

models.py

class Category(models.Model): 
    name = models.CharField(max_length=50) 

    def __unicode__(self): 
     return self.name 

class Post(models.Model): 
    category = models.ForeignKey(Category) 
    name = models.CharField(max_length=50) 
    genders = models.ManyToManyField(Gender) 

    def __unicode__(self): 
     return self.name 

views.py

def index(request): 
    categories = Category.objects.filter(post__isnull=False) 

每個FOREIGNKEY具有反向關係到其父模型，因此必須YPU一個ForeignKey的地方張貼你的模型和post__isnull =假將只返回與某些帖子有反向關係的類別...