Скачать или смотреть Efficiently Update Reverse Many-to-Many Fields in Django ORM

Learn how to efficiently update reverse many-to-many relationships in Django ORM with practical examples and techniques.
---
This video is based on the question https://stackoverflow.com/q/70439175/ asked by the user 'akash deep' ( https://stackoverflow.com/u/12448425/ ) and on the answer https://stackoverflow.com/a/70439249/ provided by the user 'willeM_ Van Onsem' ( https://stackoverflow.com/u/67579/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Django ORM query to update reverse many to many field

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Efficiently Update Reverse Many-to-Many Fields in Django ORM

Managing relationships between models is a common task in Django, especially when dealing with ManyToMany fields. In this guide, we will address the challenge of updating reverse many-to-many fields within the Django ORM. We'll explore a practical approach to efficiently perform this operation without compromising the integrity of your database.

Understanding the Problem

In our example, we have two models, Book and Author. Here’s a simplified structure of the models:

[[See Video to Reveal this Text or Code Snippet]]

Relationship Overview

A Book can be written by multiple Authors.

An Author can write multiple Books.

Given a list of updates that looks like this:

[[See Video to Reveal this Text or Code Snippet]]

We need to perform the following:

Update the authors linked to each book.

Ensure that authors not in the new list are unlinked from the respective books.

Solution Approach

To update our many-to-many fields efficiently, we can break our solution down into two main queries. Below is a step-by-step explanation of how this can be accomplished:

Step 1: Prepare the Book IDs

First, we need to extract all the book_ids from the provided data. This will allow us to efficiently manage our database queries and updates. Here’s how you can do it:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Delete Existing Relationships

Next, we will remove any existing relationships between the books and authors. By targeting only the books that were updated, we avoid unnecessarily deleting links from books that remain unchanged. The deletion can be done using the following command:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Create New Relationships

Now that we have deleted the existing relationships, we can proceed to create the new ones. This can be efficiently done using the bulk_create method, which minimizes the number of database hits. Below is the code snippet that performs this operation:

[[See Video to Reveal this Text or Code Snippet]]

Complete Example

Bringing it all together, your complete function to update the many-to-many relationships may look like this:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Updating reverse many-to-many relationships in Django ORM can be achieved efficiently with a clear understanding of how to manage relationships between models. By following the structured approach outlined in this post, you can maintain data integrity while ensuring your database updates are both effective and performant.

With Django's powerful ORM capabilities, handling such operations becomes seamless once you grasp these foundational concepts. Happy coding!