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?

Answer 1

You can use annotate() for this.

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

Answer 2

It can be done by adding one more field into only section, it's blog (I assume it helps Django to keep relation between objects (Article & Blog):

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

Tested on Django==2.2.19

Answer 3

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')