How to use ForeignKey in Django

ForeignKey is a very important concept in Django when it comes to creating relationships between different models. Here’s how you can use it:

1. Define the models

First, you need to define the models that you want to create a relationship between. For example, let’s say you have two models: Author and Book. You want to create a relationship where each book is written by an author.


<pre>
class Author(models.Model):
name = models.CharField(max_length=100)

class Book(models.Model):
title = models.CharField(max_length=200)
author = models.ForeignKey(Author, on_delete=models.CASCADE)
</pre>


In the Book model, the ForeignKey field specifies that each book is associated with an Author. The on_delete parameter specifies what should happen when the referenced Author is deleted – in this case, all associated books will also be deleted.

2. Use the ForeignKey in views and templates

Once you have defined the models, you can use the ForeignKey to create relationships between instances of the models in your views and templates. For example, if you want to display all the books written by a specific author, you can do so in your views and templates.


<pre>
author = Author.objects.get(name='John Doe')
books = Book.objects.filter(author=author)

<% for book in books %>
{{ book.title }}
<% endfor %>
</pre>


In this example, we first get the instance of the Author with the name ‘John Doe’, and then we use the ForeignKey relationship to filter all the books associated with that author and display their titles in the template.

3. Understanding the database relationship

Under the hood, the ForeignKey creates a relationship between the two models in the database. It does this by creating a foreign key constraint in the database table for the Book model, which references the primary key of the Author model. This ensures that the relationship between the two models is maintained at the database level.

So, that’s how you can use ForeignKey in Django to create relationships between different models. It’s a powerful tool that allows you to define and manage complex relationships between your data.