Скачать или смотреть Creating a Copy of a Django JSONField Value: Avoiding Unwanted Changes in Your Database

Learn how to properly create a copy of a JSONField value in Django without affecting the original data. Discover why using `copy.deepcopy()` is essential to prevent unintended changes.
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This video is based on the question https://stackoverflow.com/q/66290971/ asked by the user 'Tamdim' ( https://stackoverflow.com/u/3332516/ ) and on the answer https://stackoverflow.com/a/66290999/ provided by the user 'Abdul Aziz Barkat' ( https://stackoverflow.com/u/14991864/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: Copying a Django JSONField Value

When working with Django models that feature a JSONField, developers often find themselves needing to create a duplicate of the data stored in it. This can become tricky, especially when changes made to the copy inadvertently affect the original data stored in the database.

For instance, consider a Django model representing a user that has settings defined in a JSONField, as shown below:

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

In the view, when you fetch a user's settings and create a copy like this:

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

You might expect that changing settings_copy would not affect settings. However, you'd be surprised to find that it still alters the original settings in the database.

So, how can you create a copy of the JSONField without causing unwanted side effects?

The Solution: Use copy.deepcopy()

The key to solving this issue lies in understanding how copies work in Python, particularly when dealing with complex data structures like dictionaries.

Shallow vs. Deep Copy

Shallow Copy: When you execute settings.copy(), it creates a shallow copy of the dictionary, meaning that both the original and the copy still refer to the same internal objects. Therefore, if you modify mutable objects (like lists or other dictionaries) inside the shallow copy, those changes will be reflected in the original dictionary.

Deep Copy: Conversely, using copy.deepcopy() creates a new object recursively, meaning that all levels of the dictionary are copied, and any changes made to the new copy will not affect the original.

The Correct Code

To ensure that changes to your settings do not propagate back to the original data, you should replace the shallow copy method with a deep copy, as illustrated below:

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

Summary

By using copy.deepcopy(), you can effectively create a complete duplicate of the settings stored in a Django JSONField without any risk of inadvertently modifying the original data. This method allows for greater flexibility and security when working with your application's data.

Conclusion

If you're working with Django and need to copy a JSONField safely, remember the distinction between shallow and deep copies in Python. Always go for copy.deepcopy() when you want to ensure that your changes remain isolated from the original source. This approach will save you from potential bugs and maintain the integrity of your database.