用foreignkey注释结果

Question

我想过滤Django中的一个对象，并将其与任何结果为ForeignKey的对象一起返回。我不确定注释是否是我需要的，或其他。

这是我的模型：

class Dress(models.Model): 
    name = models.CharField(...) 
    price = models.FloatField(...) 

class ClothingSize(models.Model): 
    code = models.CharField(...) 

class DressSizeAvailable(models.Model): 
    dress = models.ForeignKey(Dress) 
    size = models.ForeignKey(ClothingSize) 

说我要过滤所有的礼服在50 $，然后与现有的尺寸显示。做这个的最好方式是什么？

我得尽可能的：

# In view 
results = Dress.objects.filter(price__lt=50) 
# How to annotate with available sizes? 

# In template 
{% for result in results %} 
    {{ result.name }}, ${{ result.price }} 
    Sizes: {{ ??? }} 
{% endfor %} 

Answer 1

### 1st solution (similar to Daniel Rosenthal's answer but with performances concern) 
results = DressSizeAvailable.objects.filter(dress__price__lt=50).select_related('dress', 'size') 
# then you can browse your DressSizeAvailables as you wish in your template. The select related allows you NOT TO query the database again when you generate your template 

### 2nd solution 
results = Dress.objects.filter(price__lt=50).prefetch_related('dresssizeavailable_set__dress') 

{% for dress in results %} 
    {{ dress.name }}, ${{ dress }} 
    Sizes: <ul> 
     {% for dsa in dress.dresssizeavailable_set %} 
      <!-- Thanks to the prefetch_related, we do not query the base again here --> 
      <li>{{ dsa.size.code }}</li> 
     {% endfor %} 
    </ul> 
{% endfor %} 

Answer 2

你需要给你的模板查询集（或类似的东西）DressSizeAvailable对象。因此，首先你需要把所有的Dress对象你有兴趣，然后根据这些礼服

所以在您的视图筛选DressSizeAvailable：

dresses = Dress.objects.filter(price__lt=50) 
dress_size_available = [] 
for dress in dresses: 
    available = DressSizeAvailable.objects.filter(dress=dress) 
    dress_size_available.append(available) 

然后渲染你的模板，它传递变量dress_size_available

您的模板可以很简单。

{% for dsa in dress_size_available %} 
    {{ dsa.dress.name }}, ${{ dsa.dress.price }} 
    Size: {{ dsa.size }} 
{% endfor %}