Boilderplate: Make A Many-To-Many Model Connection In Django

Introduction

This boilerplate creates an interface for Books and Authors to demonstarte a many-to-many connection. It assumes you've already gone through the basic site/project setup steps (i.e. Boilerplate: Create A New Django Site/Project , Boilerplate: Add Basic Template And Static File Handling In Django , and Boilerplate: Add Basic User Authencation To A Django Site ). More details are below the code in the Boilerplate Details section.

Boilerplate Steps

Perp Work

Make sure you've started the Python venv and are in the directory with: manage.py

TODO: Write up how to make sure you're in the proper vecv

Create app modules with startapp

    
    terminal commands
    
    python manage.py startapp authors
python manage.py startapp books

Make the templates directories

    
    terminal commands
    
    mkdir -p authors/templates/authors
mkdir -p books/templates/books

Update INSTALLED_APPS in site_files/settings.py

site_files/settings.py - section update
INSTALLED_APPS = [
    "django.contrib.admin",
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "django.contrib.sessions",
    "django.contrib.messages",
    "django.contrib.staticfiles",
    "authors.apps.AuthorsConfig",
    "books.apps.BooksConfig",
]

Add the top level url patterns:

site_files/urls.py - full content replacement
from django.contrib import admin
from django.urls import path
from django.urls import include

urlpatterns = [
    path("accounts/", include("django.contrib.auth.urls")),
    path("admin/", admin.site.urls),
    path("authors/", include("authors.urls")),
    path("books/", include("books.urls")),
]

Make The Authors

Make the authors model

authors/models.py - full content replacement
from django.db import models

class Author(models.Model):
    first_name = models.CharField(max_length=80)
    last_name = models.CharField(max_length=80, blank=True)

    def __str__(self):
        return f"{self.first_name} {self.last_name}"

Make the "authors/urls.py" file:

authors/urls.py - new file to create
from django.urls import path

from . import views

app_name = "authors"
urlpatterns = [
    path("", views.index, name="index"),
    path("create/", views.create, name="create"),
    path("<int:pk>/", views.view, name="view"),
    path("<int:pk>/edit/", views.edit, name="edit"),
    path("<int:pk>/delete/", views.delete, name="delete"),
]

Add the admin for the authors page

authors/admin.py - full content replacement
from django.contrib import admin

from .models import Author 

admin.site.register(Author)

Add the functions to: author/views.py

authors/views.py - full content replacement
from django.contrib.auth.decorators import login_required
from django.http import HttpResponseRedirect
from django.shortcuts import get_object_or_404, render

from .models import Author 
from .forms import AuthorForm

def index(request):
    authors_list = Author.objects.order_by("first_name").order_by("last_name")
    context = { "authors_list": authors_list }
    return render(request, "authors/index.html", context)

@login_required
def create(request):
    if request.method == "POST":
        form = AuthorForm(request.POST)
        if form.is_valid():
            form.save()
            # TODO: Update this url to be automatic 
            return HttpResponseRedirect("/authors/")
    else:
        form = AuthorForm()
        context = { "form": form }
        return render(request, "authors/create.html", context)

@login_required
def delete(request, pk):
    author = get_object_or_404(Author, pk=pk)
    if request.method == "POST":
        books = author.book_set.all()
        if len(books) > 0:
            # This makes sure we don't rely solely on the template
            # TODO: Add flash message here about not deleting
            return HttpResponseRedirect("/authors/")
        else:
            author.delete()
            return HttpResponseRedirect("/authors/")
    else:
        context = { "author": author }
        return render(request, "authors/delete.html", context)

@login_required
def edit(request, pk):
    author = get_object_or_404(Author, pk=pk)
    if request.method == "POST":
        form = AuthorForm(request.POST)
        if form.is_valid():
            author.first_name = form.cleaned_data["first_name"]
            author.last_name = form.cleaned_data["last_name"]
            author.save()
            # TODO: Figure out how to make this redirect URL automatically
            return HttpResponseRedirect(f"/authors/{pk}/")
    else:
        form = AuthorForm(instance=author)
        context = { "form": form, "author": author }
        return render(request, "authors/edit.html", context)

def view(request, pk):
    author = get_object_or_404(Author, pk=pk)
    return render(request, "authors/view.html", {"author": author})

Add the forms.py file:

authors/forms.py - new file to create
from django.forms import ModelForm

from .models import Author

class AuthorForm(ModelForm):
    class Meta:
        model = Author 
        fields = ["first_name", "last_name"]

Create the index.html template

authors/templates/authors/index.html - new file to create
<!DOCTYPE html>
<html>
<body>
  <div>
      <a href="{% url 'books:index' %}">Books</a>
      - 
      Authors
  </div>
  <hr />
  <h1>Authors</h1>
  <ul>
    {% for author in authors_list %}
      <li>
        <a href="{% url 'authors:view' author.id %}">{{ author }}</a>
      </li>
    {% endfor %}
  </ul> 
  <hr />
  <div>
    <a href="{% url 'authors:create' %}">Add An Author</a>
  </div>
</body>
</html>

Create the view.html template

authors/templates/authors/view.html - new file to create
<!DOCTYPE html>
<html>
<body>
  <div>
      <a href="{% url 'books:index' %}">Books</a>
      -
      <a href="{% url 'authors:index' %}">Authors</a>
  </div>
  <hr />
    <h1>{{ author.first_name }} {{ author.last_name }}</h1>
  <h3>Books</h3>
    <ul>
      {% for book in author.book_set.all %}
        <li><a href="{% url 'books:view' book.id %}">{{ book }}</a></li>
      {% endfor %}
    </ul>
    <hr />
    <div>
      <a href="{% url 'authors:edit' author.id %}">Edit author</a>
      - 
      <a href="{% url 'authors:delete' author.id %}">Delete author</a>
    </div>
</body>
</html>

Create the create.html template

authors/templates/authors/create.html - new file to create
<!DOCTYPE html>
<html>
<body>
<h1>Create A Author</h1>
    <form action="{% url 'authors:create' %}" method="post">
    {% csrf_token %}
    {{ form }}
    <input type="submit" value="Add Author">
  </body>
</html>

Create the edit.html template

authors/templates/authors/edit.html - new file to create
<!DOCTYPE html>
<html>
<body>
  <h1>Edit Author</h1>
    <form action="{% url 'authors:edit' author.id %}" method="post">
    {% csrf_token %}
    {{ form }}
    <input type="submit" value="Update">
</form>
</body>
</html>

Create the delete.html template

authors/templates/authors/delete.html - new file to create
<!DOCTYPE html>
<html>
<body>
    <div>
      <a href="{% url 'books:index' %}">Books</a>
      -
      <a href="{% url 'authors:index' %}">Authors</a>
    </div>
    {% if author.book_set.count > 0 %}
        <h1>Can't Delete Yet</h1>
        <div>{{ author}} is still listed as the author of:</div>
        <ul>
            {% for book in author.book_set.all %}
            <li><a href="{% url 'books:view' book.id %}">{{ book }}</a></li>
            {% endfor %}
        </ul>
    {% else %}
        <h1>Confirm You Want To Delete The Author</h1>
        <div>{{ author}}</div>
        <form action="{% url 'authors:delete' author.id %}" method="post">
            {% csrf_token %}
            <input type="submit" value="Delete" />
        </form>
    {% endif %}
</body>
</html>

Make The Books

Make the books and book_authors models

books/models.py - full content replacement
from django.db import models

from authors.models import Author

class Book(models.Model):
    title = models.CharField(max_length=200)
    authors = models.ManyToManyField(Author, blank=True, through="BookAuthor")

    def __str__(self):
        return self.title

class BookAuthor(models.Model):
    book = models.ForeignKey(Book, on_delete=models.CASCADE)
    author = models.ForeignKey(Author, on_delete=models.PROTECT)

Make the "books/urls.py" file:

books/urls.py - new file to create
from django.urls import path

from . import views

app_name = "books"
urlpatterns = [
    path("", views.index, name="index"),
    path("create/", views.create, name="create"),
    path("<int:pk>/", views.view, name="view"),
    path("<int:pk>/edit/", views.edit, name="edit"),
    path("<int:pk>/delete/", views.delete, name="delete"),
]

Add the admin for the books page

books/admin.py - full content replacement
from django.contrib import admin

from .models import Book 

admin.site.register(Book)

Add the functions to: book/views.py

books/views.py - full content replacement
from django.contrib.auth.decorators import login_required
from django.http import HttpResponseRedirect
from django.shortcuts import get_object_or_404, render

from .models import Book 
from .forms import BookForm

def index(request):
    books_list = Book.objects.order_by("title")
    context = {"books_list": books_list}
    return render(request, "books/index.html", context)

@login_required
def create(request):
    if request.method == "POST":
        form = BookForm(request.POST)
        if form.is_valid():
            form.save()
            # TODO: Update this url to be automatic 
            return HttpResponseRedirect("/books/")
    else:
        form = BookForm()
        context = { "form": form }
        return render(request, "books/create.html", context)

@login_required
def delete(request, pk):
    book = get_object_or_404(Book, pk=pk)
    if request.method == "POST":
        book.delete()
        # TODO: set this url automatically
        return HttpResponseRedirect("/books/")
    else:
        context = { "book": book }
        return render(request, "books/delete.html", context)

@login_required
def edit(request, pk):
    book = get_object_or_404(Book, pk=pk)
    if request.method == "POST":
        form = BookForm(request.POST)
        if form.is_valid():
            book.title = form.cleaned_data["title"]
            book.authors.set(form.cleaned_data["authors"])
            book.save()
            # TODO: Figure out how to make this redirect URL automatically
            return HttpResponseRedirect(f"/books/{pk}/")
    else:
        form = BookForm(instance=book)
        context = { "form": form, "book": book }
        return render(request, "books/edit.html", context)

def view(request, pk):
    book = get_object_or_404(Book, pk=pk)
    return render(request, "books/view.html", {"book": book})

Add the forms.py file:

books/forms.py - new file to create
from django.forms import ModelForm

from .models import Book

class BookForm(ModelForm):
    class Meta:
        model = Book 
        fields = ["title", "authors"]

Create the index.html template

books/templates/books/index.html - new file to create
<!DOCTYPE html>
<html>
<body>
  <div>
      Books 
      -
      <a href="{% url 'authors:index' %}">Authors</a>
  </div>
  <hr />
  <h1>Books</h1>
  <ul>
    {% for book in books_list %}
      <li>
        <a href="{% url 'books:view' book.id %}">{{ book }}</a>
        {% if book.authors.count > 0 %}
          by: {% for author in  book.authors.all %}
          {{ author.first_name }} 
          {{ author.middle_string }}
          {{ author.last_name }}{% if not forloop.last %}, {% endif %}
          {% endfor %}
        {% endif %}
      </li>
    {% endfor %}
  </ul> 
  <hr />
  <div>
    <a href="{% url 'books:create' %}">Add A Book</a>
  </div>
</body>
</html>

Create the view.html template

books/templates/books/view.html - new file to create
<!DOCTYPE html>
<html>
<body>
  <div>
      <a href="{% url 'books:index' %}">Books</a>
      -
      <a href="{% url 'authors:index' %}">Authors</a>
  </div>
  <hr />
  <h1>{{ book }}</h1>
  <div>
      {% if book.authors.count > 0 %}
        by: 
        {% for author in  book.authors.all %}
        <a href="{% url 'authors:view' author.id %}">
          {{ author.first_name }} 
          {{ author.last_name }}</a>{% if not forloop.last %}, {% endif %}
        {% endfor %}
      {% endif %}
  </div>
  <hr />
  <div>
    <a href="{% url 'books:edit' book.id %}">Edit book</a>
    - 
    <a href="{% url 'books:delete' book.id %}">Delete book</a>
  </div>
</body>
</html>

Create the create.html template

books/templates/books/create.html - new file to create
<!DOCTYPE html>
<html>
<body>
    <div>
      <a href="{% url 'books:index' %}">Books</a>
      -
      <a href="{% url 'authors:index' %}">Authors</a>
    </div>
    <hr />
    <h1>Create A Book</h1>
    <form action="{% url 'books:create' %}" method="post">
    {% csrf_token %}
    {{ form }}
    <input type="submit" value="Create Book">
    <div>
        You have to make new authors <a href="{% url 'authors:create' %}">on this page</a>
    </div>
  </body>
</html>

Create the edit.html template

books/templates/books/edit.html - new file to create
<!DOCTYPE html>
<html>
<body>
  <h1>Edit Book</h1>
    <form action="{% url 'books:edit' book.id %}" method="post">
    {% csrf_token %}
    {{ form }}
    <input type="submit" value="Update">
</form>
</body>
</html>

Create the delete.html template

books/templates/books/delete.html - new file to create
<!DOCTYPE html>
<html>
<body>
    <div>
      <a href="{% url 'books:index' %}">Books</a>
      -
      <a href="{% url 'authors:index' %}">Authors</a>
    </div>
    <h1>Confirm You Want To Delete The Book</h1>
    <div>{{ book }}</div>
    <form action="{% url 'books:delete' book.id %}" method="post">
        {% csrf_token %}
        <input type="submit" value="Delete">
    </form>
</body>
</html>

Finishing Up

Run the migrations

    
    terminal commands
    
    python manage.py makemigrations authors
python manage.py migrate authors
python manage.py makemigrations books 
python manage.py migrate books

Start the server:
terminal commands
```
python manage.py runserver
```
Visit the page:

link

http://127.0.0.1:8000/books/ ↗

Boilerpage Details

This boilerplate demonstrates a basic many-to-many connection between database items.
The example uses Books and Authors.
You can view books and authors without being logged in.
You have to be logged in in order to add/edit/delete books and authors.
Each Book can have zero or more Authors.
Each Author can have zero or more Books.
You can delete a Book at any point.
You can only delete Authors when they don't have any books associated with them.
Author names have to have a first name, but the last name is not required.

~ fin ~