15.6. Models in Django: Database Migrations

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Django is a high-level web development framework, written in Python, that promotes rapid development and clean, pragmatic design. One of Django's most powerful features is its Object-Relational Mapper (ORM), which lets you interact with your database as if you were writing pure Python. In this context, let's discuss a crucial part of Django's ORM - Templates and Database Migrations.

Models in Django are the single, definitive source of information about your data. They contain the essential fields and behaviors of the data you are storing. In general, each model maps to a single database table. Each model is a Python class that inherits from django.db.models.Model, where each attribute of the class represents a database field.

For example, if you are building a blog system, you might have a 'Post' template like this:

from django.db import models

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    pub_date = models.DateTimeField('date published')

Here, each instance of 'Post' will correspond to a row in a database table, and each field class (CharField, TextField, DateTimeField) will be converted to an appropriate database field type.

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Once you define your models, Django provides a powerful tool to help you manage your database called migrations. Migrations are how Django stores changes to your models (and therefore your database schema) - they're just files on disk that describe the changes to be made to your database. Django keeps track of which ones have been applied and provides tools for creating new migrations based on changes you've made to your models.

For example, after defining the 'Post' template above, you can create a new migration with the command:

python manage.py makemigrations blog

Where 'blog' is the name of the Django app that contains the 'Post' model. This will create a new migration file in your app's 'migrations' directory, which Django will use to change the database schema.

To apply the migration to your database, you use the command:

python manage.py migrate

This will apply all pending migrations to your database, changing the database schema to match your current models.

When working with migrations, it is important to remember that you should always use migrations to change your database schema. This includes adding or changing templates, changing fields in existing templates, or even changing the name of a field. Migrations allow you to make these changes in a controlled and consistent manner, ensuring that your database schema always matches the current state of your models.

In summary, Django models and database migrations are powerful tools that allow you to work with data in a Pythonic way. With them, you can focus on writing your application, knowing that Django will handle the database details for you.

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8115.7. Models in Django: Database Queries