Model-View-Controller (MVC)¶

In MVC, the model represents the information (the data) of the application and the business rules used to manipulate the data
The view corresponds to elements of the user interface such as text, checkbox items, and so forth;
The controller manages details involving the communication to the model of user actions.

Model¶

It defines the schema of the database, including tables, fields, and relationships.
Models are typically defined in models.py files within Django apps.
We call the Data bit - the “Model” or Data Model

View¶

The HTML, CSS, etc. which makes up the look and feel of the application.
Views in Django are typically functions or classes defined in views.py files within Django apps.
We call the “making the next HTML” bit the “View” or “Presentation Layer”

Template¶

Templates in Django are responsible for the user interface.
They define the structure and presentation of the data to be displayed to the user. Django uses its built-in templating engine to render dynamic content based on data provided by views.

Controller¶

The code that does the thinking and decision making
We call the handling of input and the general orchestration of it all the “Controller”

Object Relational Mapping (ORM)¶

Object-Relational Mapping (ORM) in Django allows you to interact with your database using high-level object-oriented constructs instead of directly writing SQL queries.

1.Define a model (table)¶

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=50)
    publication_date = models.DateField()

2.Create Migration and Apply to Database¶

Django provides a command-line interface to generate database migrations based on your model definitions.

cmd
python manage.py makemigrations
python manage.py migrate

This creates the necessary database tables based on your models.

3.a Input to table / database¶

Now, you can use the Book model in your Python code.

For example, to create a new book:

from myapp.models import Book
from datetime import date

# Create a new book
book = Book.objects.create(
    title='Python Programming',
    author='Guido van Rossum',
    publication_date=date(1995, 1, 1)
)

3.b Query the database¶

You can query the database using Django's ORM to retrieve objects.

For example, to retrieve all books written by a specific author:

# Query all books by a specific author
books = Book.objects.filter(author='Guido van Rossum')

for book in books:
    print(book.title)

3.c CREATE, READ, UPDATE and DELETE (CRUD) in the ORM¶

# Create a new user and save it to the database
u = User(name = "Sally", email = "a2@umich.edu")
u.save()

# Retrieve all users from the database and display their values
User.objects.values()

# Filter users by email and display their values
User.objects.filter(email = "ted@umich.edu").values()
User.objects.filter(email = "ted@umich.edu").delete()
User.objects.values()

# Update the name of the user(s) with a specific email
User.objects.filter(email = "csev@umich.edu").update(name = 'Charles')
User.objects.values()

# Retrieve all users from the database, order them by email, and display their values
User.objects.values().order_by("email")

# Retrieve all users from the database, order them by name in descending order, and display their values
User.objects.values().order_by("-name")

Migrations: From model to Database¶

The make migrations command reads all the models.py files in all the applications, end creates / evolves the migration files
Guided by the applications listed in settings.py