Accessing ForeignKey Fields Asynchronously in Django

The SynchronousOnlyOperation error you're encountering is because accessing a ForeignKey field directly in an asynchronous context triggers a database query, which is a blocking operation. In Django's asynchronous views, you need to use the asynchronous variants of methods that might block.

The Problem

When you access user.post_1 in an asynchronous view, Django attempts to fetch the related Post object from the database using a synchronous query, which is not allowed in an asynchronous context.

Solution

You need to use the asynchronous version of the related field accessor. For ForeignKey fields, you can use the aget_related() method:

PYTHONCopied
async def index(request):
    user = await request.auser()
    if not user.is_authenticated:
        return HttpResponseRedirect(reverse('account:login') + f'?next={request.path}')
    
    # Asynchronously fetch related objects
    user_post_1 = await user.aget_related('post_1')
    user_post_2 = await user.aget_related('post_2')
    
    return render(request, 'account/detail.html', context={ 
        'user_post_1': user_post_1,
        'user_post_2': user_post_2,
    })

Alternative Approach

If you need to fetch multiple related objects, you can also use select_related() when fetching the user to avoid additional queries:

PYTHONCopied
async def index(request):
    # Get user with related posts in a single query
    user = await CustomUser.objects.select_related('post_1', 'post_2').aget(id=request.user.id)
    if not user.is_authenticated:
        return HttpResponseRedirect(reverse('account:login') + f'?next={request.path}')
    
    return render(request, 'account/detail.html', context={ 
        'user_post_1': user.post_1,  # No additional query needed now
        'user_post_2': user.post_2,
    })

This approach prefetches the related objects in the initial query, so accessing them later doesn't trigger additional database queries.

Remember that in Django's asynchronous context, any method that might cause a database query needs to use the asynchronous variant (prefixed with 'a') and be awaited.