Django - Display a ModelForm foreign key field

Question

Model & Form

class Book(models.Model):
  author = models.ForeignKey(User)
  name = models.CharField(max_length=50)

class BookForm(forms.ModelForm):
  class Meta:
    model = Book
    widgets = {
      'author': forms.HiddenInput(),
    }

This book form doesn't allow changing the author

Template

But I'd like to display his firstname

<form action="/books/edit" method="post">{% csrf_token %}
  {{ form.author.label }}: {{ form.author.select_related.first_name }}
  {{ form.as_p }}
</form>

Question

Of course form.author.select_related.first_name doesn't work

How can I display the firstname of the author ?

Answer 1

This should work:

<form action="/books/edit" method="post">{% csrf_token %}
  {{ form.author.label }}: {{ form.instance.author.first_name }}
  {{ form.as_p }}
</form>

But you cannot use this form for creating books, only for updating, this won't work if the author is not set on instance.