069-Updating Models & Migrations-opendir.cloud.
*Lecture 069-Updating Models & Migrations*
In this lecture, we will be discussing how to update models and migrations in Django. We will cover the following topics:
How to make changes to models
How to create migrations
How to apply migrations
How to rollback migrations
*Making changes to models*
When you make a change to a model, you need to create a migration. A migration is a set of changes that can be applied to the database to bring it up to date with the latest version of the model.
To create a migration, you can use the `makemigrations` command. This command will create a new migration file in the `migrations` directory for the app that contains the model.
The migration file will contain a list of the changes that need to be made to the database. These changes can be things like adding new fields, removing fields, or changing the data type of a field.
*Creating migrations*
Once you have created a migration, you can apply it to the database using the `migrate` command. This command will apply all of the changes in the migration to the database.
*Applying migrations*
If you make a mistake and need to undo a migration, you can use the `rollback` command. This command will undo the changes in the most recent migration.
*Rolling back migrations*
It is important to note that you can only rollback migrations that have not been applied to the database. If you have applied a migration and then made changes to the model, you will not be able to rollback the migration.
*In this lecture, we will be demonstrating how to update models and migrations in Django. We will be using the following models:*
```python
from django.db import models
class Book(models.Model):
title = models.CharField(max_length=255)
author = models.ForeignKey(Author, on_delete=models.CASCADE)
class Author(models.Model):
name = models.CharField(max_length=255)
```
*We will be making the following changes to the models:*
Adding a `genre` field to the `Book` model
Changing the `name` field on the `Author` model to be nullable
*We will then create migrations for these changes and apply them to the database.*
*Once the migrations have been applied, we will be able to see the changes in the database.*
*We will also be demonstrating how to rollback migrations.*
*By the end of this lecture, you will be able to update models and migrations in Django.*
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