Lesson 28 -  Linking Data Types

LEARN

Today

• Testing data changes
• Add new data types (Data, Views, Routes, Tests)

Django for Beginners - Chapter 15

• Comments on Articles
• Articles app
• URL, Templates, Views
• ForeignKey - Comment, Article

Relational Data

• Data table point to each other
• Objects live in the tables
• Reduce the duplicate information
• Databases are joined by a query

Foreign Key

• Points to a record in another table
• Saves to ID of the record
• Guarantees that data is consistent
• Data duplication is removed

Relational Example

• Chapters belong to a Book
• Chapter Data Record
  • book (points to a book ID)
  • order
  • title

Author Data Model

Create a representation for Authors

```python class Author(models.Model): name = models.CharField(max_length=200) user = models.ForeignKey(User, on_delete=models.CASCADE)

```

Book Data Model

Create a representation for Chapters in the Book

python class Book(models.Model): author = models.ForeignKey(Author, on_delete=models.CASCADE) title = models.CharField(max_length=200)

Chapter Data Model

Create a representation for Chapters in the Book

python class Chapter(models.Model): book = models.ForeignKey(Book, on_delete=models.CASCADE) order = models.IntegerField() title = models.CharField(max_length=200)

Custom Queries in List View

• Find only matching objects
• Pass reference object by ID on URL
• Use get_queryset to filter objects

Book Builder Demo

• Implement data design (Author, Book, Chapter)
• Author <-- Book <-- Chapter
• Views support proper queries
• Book builder style
• Tests for Data/Views (Author, Book, Chapter)

Author's Books

List the Book by an Author

book/views.py

```python

urls.py

path('author/', AuthorDetailView.as_view(), name='author_detail'),

class AuthorDetailView(DetailView): template_name = 'author_detail.html' model = Author

def get_context_data(self, **kwargs):
    author = Author.objects.get(pk=self.kwargs['pk'])
    return dict(object=author, books=Book.objects.filter(author=author))

```

Chapters in Book

Show the Chapters in the Book in detail view

templates/book_detail.html

```html

{% for chapter in chapters %} {% endfor %}

{{ chapter.book }}

Chapter {{ chapter.order }} - {{ chapter.title }}

Edit

Delete

```

BUILD

Testing Failure

• Personal story of process failure
• Changes to object model without testing
• Spent four hours trying to find the error

Demo Code

• Demo Code
• Follow along with my source code
• Clone my repo and edit the code

Project 10 - Superhero News

• Views
  • Query for Articles about each Hero in HeroDetailView
  • Add the article list to hero detail template
• Data
  • Add hero as ForeignKey in Article
  • Migrate
• Tests
  • Hero Data
  • Hero Views
  • Article Data
  • Article Views

Project 10 - Views

• Superhero Selector Page
• Profile Tab
• News Tab
• Article Views
• Hero Views

Project 10 - Data

• Investigator Data Type
• Investigator <-- Hero <-- Article
• Views support proper queries
• Hero News  style

Project 10 - Tests

• Data/Views
• Investigator, Hero, Article