Add model relation to ModelForm before saving - django

Question

models.py
from django.db import models
class Author(models.Model):
name = models.CharField(max_length=32)
class Article(models.Model):
author = models.ForeignKey(Author, on_delete=models.SET_NULL, null=True)
content = models.TextField()
forms.py
from django import forms
from .models import Article
class ArticleForm(forms.ModelForm):
class Meta:
model = Article
fields = ['content']
In my web application, the author logs in and writes an article. So clearly, when the author is presented with an ArticleForm, he/she does not need to fill in the author field in the ArticleForm because the application already knows who the author is through the use of session variables.
This is the way I tried to add the author:
views.py
from django.shortcuts import render, redirect, get_object_or_404
from django.contrib.auth.decorators import login_required
from .models import Article
from .forms import ArticleForm
#login_required
def new_article(request):
author_name = request.session['author_name']
author = Author.objects.get(name=author_name)
if request.method == 'POST':
form = ArticleForm(request.POST)
if form.is_valid():
form.save(commit=False)
form.author = author # I suspect the mistake is here
# I also tried form.author = author.id
form.save()
return redirect('success')
else:
form = ArticleForm()
return render(request, 'writings/new_article.html', {'form': form})
When I look at the database table, the author_id column is always NULL. What is wrong with my approach? How do I add a model relation before saving a ModelForm?

Answer 1

Capture the object returned from form.save(commit=False) and modify that rather than the form. EG:
if form.is_valid():
article = form.save(commit=False)
article.author = author
article.save()
return redirect('success')