整理註釋和使用價值（），而在Django的ORM返回註釋

Question

我試圖運行下面的查詢：

labels = AssetLabel.objects.filter(organization=request.organization).annotate(num_assets=Count('asset')) 
labels = list(labels.order_by('-num_assets')[:20].values('id', 'name')) 

這給了我一個錯誤：

FieldError: Cannot resolve keyword 'num_assets' into field. Choices are: asset, id, name, organization 

如果我添加num_assets到.values()，那麼我不會收到錯誤。但是，我不希望num_assets被返回。有沒有辦法做到這一點？

Answer 1

你應該values使用前annotate，從doc的例子：

You should also note that average_rating has been explicitly included in the list of values to be returned. This is required because of the ordering of the values() and annotate() clause.

ValuesQuerySet總是包含註釋字段，ITER它來刪除該字段，

values = labels.order_by('-num_assets')[:20].values('id', 'name') 
for value in values: 
    value.pop('num_assets') 

Answer 2

檢查功能extra，它有一個叫order_by的參數，所以你可以使用這個功能來定購給定的QuerySet

https://docs.djangoproject.com/en/dev/ref/models/querysets/#django.db.models.query.QuerySet.extra

我想這可能是這樣的：

labels = AssetLabel.objects. \ 
    filter(organization=request.organization). \ 
    extra(
     select={'num_assets': "Count('asset')"}, 
     order_by=['num_assets'] 
    )