{"id":1455,"date":"2022-09-11T18:21:51","date_gmt":"2022-09-11T18:21:51","guid":{"rendered":"https:\/\/zerotobyte.com\/?p=1455"},"modified":"2022-09-12T08:53:41","modified_gmt":"2022-09-12T08:53:41","slug":"how-to-use-django-order-by","status":"publish","type":"post","link":"https:\/\/zerotobyte.com\/how-to-use-django-order-by\/","title":{"rendered":"How to use Django order_by?"},"content":{"rendered":"\n
Sorting data stored in the database can often be crucial for your application. Luckily, Django has integrated methods over querysets that help us do that without writing SQL queries.<\/p>\n\n\n\n
Django order_by<\/code> is a method that sorts existing queryset by fields passed as arguments. Queryset can be sorted in ascending, descending, or random order (depending on arguments).<\/strong><\/p>\n\n\n\n
Why can’t we sort queryset using Python to manipulate data?<\/strong> Sorting using Python would be much slower and expensive – converting the queryset to list will evaluate it, bringing performance issues.<\/strong><\/p>\n\n\n\n
All of the outputs and queries are made on the following models:<\/p>\n\n\n\n
from django.db import models\n\nclass Author(models.Model):\n first_name = models.CharField(max_length=512)\n last_name = models.CharField(max_length=512)\n\nclass Book(models.Model):\n title = models.CharField(max_length=512)\n author = models.ForeignKey(Author, on_delete=models.CASCADE)<\/pre>\n\n\n\n
The database is prepopulated with data:<\/p>\n\n\n\n
Authors table.<\/strong><\/p>\n\n\n\n
id<\/strong><\/td>
first_name<\/strong><\/td>
last_name<\/strong><\/td><\/tr>
1<\/td>
William<\/td>
Shakespeare<\/td><\/tr>
2<\/td>
Miguel<\/td>
de Cervantes<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
Books table.<\/strong><\/p>\n\n\n\n
id<\/strong><\/td>
title<\/strong><\/td>
author_id<\/strong><\/td><\/tr>
1<\/td>
Hamlet<\/td>
1<\/td><\/tr>
2<\/td>
Romeo and Juliet<\/td>
1<\/td><\/tr>
3<\/td>
Macbeth<\/td>
1<\/td><\/tr>
4<\/td>
Don Quixote<\/td>
2<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
Django order_by ascending order<\/h2>\n\n\n\n
Most common and default way of sorting while using Django\u2019s order_by<\/code> method. Based on the type of data we are sorting, we get an ascending order<\/strong> – for numbers; we sort lowest numbers first, strings are sorted alphabetically (from A to Z), date-times from lowest dates to highest (lowest being first).<\/p>\n\n\n\n
Parameters we can send to Django order_by in the Authors table are id<\/code>, first_name<\/code>, last_name<\/code>, or all combined. For example, for the Book model, we can send id<\/code>, title<\/code>, author_id<\/code>, author__first_name<\/code>, and author__last_name<\/code>.<\/p>\n\n\n\n
Accordingly, translating ORM query to SQL query, we get:<\/p>\n\n\n\n
SELECT * FROM \"book\" INNER JOIN \"author\" ON (\"book\".\"author_id\" = \"author\".\"id\") ORDER BY \"author\".\"first_name\" ASC<\/pre>\n\n\n\n
Two tables are connected using INNER JOIN and matching ids from the authors’ foreign keys.<\/strong> Then, after the new table is created, we sort it by the author’s first name.<\/p>\n\n\n\n
Django order_by descending order<\/h2>\n\n\n\n
Contrary to ascending order, another Django order_by option is descending order.<\/strong> Descending order – for numbers, we sort the highest numbers first, strings are sorted alphabetically (from Z to A), date-times from highest dates to lowest (highest being first).<\/p>\n\n\n\n
Descending order can be achieved by adding the prefix ‘-‘ to the argument in the order_by method.<\/strong><\/p>\n\n\n\n
SELECT * FROM \"author\" ORDER BY \"author\".\"first_name\" DESC<\/pre>\n\n\n\n
INFO<\/strong> - \nYou can achieve the same result by using the default Django order_by method (without prefix) but adding the .reverse() method.\n<\/pre>\n\n\n\n
The SQL query is the same as the above.<\/p>\n\n\n\n
SELECT * FROM \"author\" ORDER BY \"author\".\"first_name\" DESC<\/pre>\n\n\n\n
Django order_by random order<\/h2>\n\n\n\n
Django order_by offers the possibility of random order by using the operator ‘?’.<\/strong> However, as the name suggests, if using this method, order_by mixes up objects in queryset in no particular order.<\/p>\n\n\n\n
As you can imagine, an SQL query is created supporting random queryset generation.<\/p>\n\n\n\n
SELECT * FROM \"book\" ORDER BY RAND() ASC<\/pre>\n\n\n\n
WARNING<\/strong> - Do not use in production! Random order queries are slow and expensive.<\/pre>\n\n\n\n
Django order_by multiple fields<\/h2>\n\n\n\n
Previous examples covered how to order and change its order, but often we want to sort our queryset by multiple fields based on the priority of the fields – field passed first has bigger priority than field passed second, etc.<\/p>\n\n\n\n
Book objects are first sorted by author first_name<\/code> (Miguel being first and William second) – that’s why Don Quixote is first in resolving queryset. Books written by William are then sorted by title<\/code> in ascending order.<\/p>\n\n\n\n
Previous query is translated to:<\/p>\n\n\n\n
SELECT * INNER JOIN \"author\" ON (\"book\".\"author_id\" = \"author\".\"id\") ORDER BY \"author\".\"first_name\" ASC, \"book\".\"title\" ASC<\/pre>\n\n\n\n
Summary<\/h2>\n\n\n\n
Django order_by<\/code> method is a popular method for sorting querysets using queries on the database. Order_by can sort queryset in ascending, descending, and random order with one or multiple fields.<\/p>\n","protected":false},"excerpt":{"rendered":"
Sorting data stored in the database can often be crucial for your application. Luckily, Django has integrated methods over querysets … <\/p>\n