Selecting specific fields using select_related in Django

Question

I have two models Article and Blog related using a foreign key. I want to select only blog name while extracting the article.

articles = Articles.objects.all().select_related('blog__name')

The query generated shows that it selected all the fields from the Blog model. I tried using only() and defer() with select_related but both didn't work out.

articles = Articles.objects.all().select_related('blog__name').only('blog__name', 'title', 'create_time')

The above query resulted in error: Invalid field name(s) given in select_related: Choices are: blog

How do i generate a query so that only article fields and blog name is selected?

Solution 1

You can use annotate() for this.

>>> a = Articles.objects.annotate(blog_name=F('blog__name')).first()
>>> a.title
>>> a.blog_name

Solution 2

select_related should be use on the whole model, and then you can filter it more. This will work:

Articles.objects.select_related('blog').only('blog__name', 'title', 'create_time')

Comments

[anonDuck]

Using .values returns dictionary instead of queryset object, which makes it useless to use the relations like 'file.url' or 'file.name' in the templates or view. Is there any other way possible?

[T. Opletal]

@RA123 I edited my answer. Tried it and this way it works for me

[anonDuck]

This is also not working. I'm on Django 1.8. It gives the following error - "Invalid field name(s) given in select_related: 'blog'. Choices are: blog" When i remove '__name' from 'blog__name' in 'only', it works fine but fetches all the fields.

[lechup]

It's working on 1.10, I'm using it with QuerySet.defer(), thanks!

[Shashank Hegde]

This is not the expected answer. The below one solves the purpose.

[Mohammed Shareef C]

Sometimes, this serves the purpose. anyway both are significant

[Clint Eastwood]

original question was: "How do i generate a query so that only article fields and blog name is selected?" This is fetching all fields from Blog, right? If so, it wouldn't answer the question properly. Correct?