用foreignkey註釋結果

Question

我想過濾Django中的一個對象，並將其與任何結果爲ForeignKey的對象一起返回。我不確定註釋是否是我需要的，或其他。

這是我的模型：

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) 

說我要過濾所有的禮服在50 $，然後與現有的尺寸顯示。做這個的最好方式是什麼？

我得儘可能的：

# 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

你需要給你的模板查詢集（或類似的東西）DressSizeAvailable對象。因此，首先你需要把所有的Dress對象你有興趣，然後根據這些禮服

所以在您的視圖篩選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) 

然後渲染你的模板，它傳遞變量dress_size_available

您的模板可以很簡單。

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