I wish to display, in the admin list, a count of the child object collection for that parent item

Using Django
1

I am very new to Django, and I have more or less gone through all the tutorial (polls). I have used .net mvc, PHP Larravel, and Node JS to build some pretty big sites on the past, so I am not unfamiliar with using frameworks.

One thing that seems new to me (based on my experience with the other 3 frameworks), is the admin aspect of Django. If I built my own admin (like what I have done with previous frameworks), I likely would not come across this issue. I am mainly practicing at the moment. My app is (I am not looking for a critique on my site!):

Books!

Books have Chapters

Chapters have Paragraphs

In the admin list of books, all I want to do is show the chapter COUNT. All I can manage is to get the list of ALL chapters in the entire database.

I will try as well as I can to only include what is necessary. model.py and admin.py:

#model.py
from django.db import models
from django.db.models import Count #Not used yet!

# Create your models here.
class Book(models.Model):
    title = models.CharField(max_length=255)
    author = models.CharField(max_length=255)
    genre = models.CharField(max_length=200)
    cover_image = models.CharField(max_length=255)
    summary = models.TextField()
    pub_date = models.DateTimeField("date published")
    def __str__(Book):
        return Book.title
    def chapter_count(self):
        return Chapter.objects.count()
    
    
class Chapter(models.Model):
    book = models.ForeignKey(Book, on_delete=models.CASCADE)
    title = models.CharField(max_length=255)
    chapter_image = models.CharField(default='noimage', max_length=255)
    chapter_number = models.IntegerField(default=0)
    def __str__(Chapter):
        return Chapter.title

Specifically note the chapter_count method!

#This is VERY abbreviated! Therefore some code is not shown for brevity reasons:
from django.contrib import admin

from .models import Paragraph, Chapter, Book

#...
class BookAdmin(admin.ModelAdmin):
    fieldsets = [
        (None, {"fields": ["title"]}),
        (None, {"fields": ["author"]}),
        (None, {"fields": ["genre"]}),
        (None, {"fields": ["summary"]}),
        (None, {"fields": ["cover_image"]}),
        ("Date information", {"fields": ["pub_date"], "classes": ["collapse"]}),
    ]
    
    inlines = [ChapterInline]
    list_display = [ "title", "author", "chapter_count", ]
#...
#EDIT: thought I better just add this:
admin.site.register(Book, BookAdmin)

That chapter count gives ALL chapters in database.

In either model or admin.py, I would just like to know how to ensure it only shows the chapter_count for that specific Book. I do not know if to do it in model or admin.py

NOTE: Obviously if I know how to do this with Book/ Chapters, I can do exactly the same for Chapters/ Paragraphs.

Sorry for the very long post! Any help would be nice.

2

Django automatically creates reverse releationships for any Foreign Keys or other relationships.

By default the name of this property is <related_model_name>_set so you method can change to the following:

class Book(models.Model):
    ....
    def chapter_count(self):
        return self.chapter_set.count()
3

Oh, bravo nanorepublica!

I just knew based on experience with other frameworks this would be elegant and simple. I did so many searches and went to countless stack-overflow posts, but just could not unpack it sensibly to my situation.

I have of course already used that exact notation (chapter_set) in the view template, based on the Polls tutorial (as well .count (without brackets) that I worked out by accident). I think now I have understood that notation for both view (although I should probably say “template-view”, as in MVT as opposed to MVC) and model, it is making much more sense now.