CRUD Design Pattern

Overview

Goals

Use data models with the Django ORM to update the database records.

Support CREATE, READ, UPDATE, DELETE operations on each data type.

Ensure database integrity.

Work with data using Python.

Steps

• Define data model as a Python class
• Use operations defined in Django models.Model to do CRUD
• Create named access functions for clarity

Data

Data Model

```python from django.db import models

class Book(models.Model): title = models.CharField(max_length=200) subtitle = models.CharField(max_length=200, null=True, blank=True) author = models.ForeignKey(Author, on_delete=models.CASCADE, editable=False) ```

CRUD

CREATE

book/book.py

```python from book.models import Book

Create one object

b = Book.objects.create(title='Dune', author=herbert)

Create if needed

b = Book.objects.get_or_create(title='Dune', author=herbert)[0]

Create function

def create_book(title, author, subtitle): c = Book.objects.get_or_create(title=title, author=author)[0] c.subtitle = subtitle c.save() return c ```

READ

book/book.py

```python

Query for one object

book = Book.objects.get(title=title)

book.title

Query for list of objects

books = Book.objects.filter(author=author)

for b in books: print(b.title, b.author)

Books by author

def books_by_author(author): return Book.objects.filter(author=author) ```

UPDATE

book/book.py

```python

Edit one object

book = Book.objects.get(title=title)

book.title = 'Children of Dune' book.subtitle = 'Sequel'

book.save() ```

DELETE

book/book.py

```python

Delete one object

book = Book.objects.get(title=title) book.delete()

Delete multiple objects

Book.objects.filter(author=author).delete() ```

Tests

book/tests.py

```python from django.test import TestCase

class BookDataTest(TestCase):

def test_book_add(self):
    pass

def test_book_list(self):
    pass

def test_book_detail(self):
    pass

def test_book_edit(self):
    pass

def test_book_delete(self):
    pass

```