{"id":594,"date":"2022-01-08T14:53:18","date_gmt":"2022-01-08T14:53:18","guid":{"rendered":"https:\/\/zerotobyte.com\/?p=594"},"modified":"2022-01-14T23:31:41","modified_gmt":"2022-01-14T23:31:41","slug":"django-queryset-basic-queries-with-examples","status":"publish","type":"post","link":"https:\/\/zerotobyte.com\/django-queryset-basic-queries-with-examples\/","title":{"rendered":"Django QuerySet – Basic Queries With Examples"},"content":{"rendered":"\n

After learning how to define models and apply database migrations in Django<\/a>, it\u2019s time to learn how to query that data. Building a Django web application or REST API in almost all cases implies communicating with the database. To make your life easier, Django comes with a database-abstraction API, also known as Django QuerySet API<\/strong>, that helps you interact with the database through numerous out-of-the-box methods.<\/p>\n\n\n\n

In this article, you\u2019ll learn what Django QuerySet is, how to use it, and what best practices you should follow. After you finish reading this article, you can also learn more advanced techniques by reading part 2: Django QuerySet \u2013 Set Operations, Aggregations, Q and F Objects Explained<\/a>.<\/p>\n\n\n\n

What is Django QuerySet API?<\/h2>\n\n\n\n

QuerySet API includes methods for creating, retrieving, updating, and deleting data<\/strong> (CRUD operations) as well as more advanced methods for aggregation, optimization, and set operations<\/strong>. These methods typically return a collection of queries, also called the queryset. Querysets are lazy, which means the database query isn\u2019t executed immediately but only when the queryset is evaluated<\/strong>.<\/p>\n\n\n\n

You may be wondering how the QuerySet API works under the hood. To answer that question, you must first understand Django\u2019s ORM (Object-Relational Mapper). It is one of the most powerful Django features, enabling you to write queries in a pythonical way instead of writing raw SQL queries. So, ORM allows you to interact with the database through objects and their methods instead of SQL statements<\/strong>. <\/p>\n\n\n\n

By executing provided methods, ORM translates Python code to SQL statements that are executed in the database. This process is also known as the queryset evaluation – rows matched by the QuerySet are fetched from the database and converted into Django objects<\/strong>. Fetched results are then stored inside the QuerySet\u2019s built-in cache<\/strong>, reducing the need for unnecessary subsequent queries towards the database. Nice little trick there, Django!<\/p>\n\n\n\n

When are Django querysets evaluated?<\/h2>\n\n\n\n

Django querysets are lazy. The database will not be hit until a specific action is performed. You can even chain multiple QuerySet methods together without triggering the additional database hits<\/strong>. That\u2019s Django\u2019s way of optimizing the number of queries performed towards the database. Still, to retrieve results from the database, queryset must be evaluated at some point<\/strong>. Actions that will evaluate the queryset are:<\/p>\n\n\n\n