How to Change an array-valued Key in JSON Using MySQL's JSON_REPLACE and JSON_ARRAY

A step-by-step guide on how to update an array-valued key in JSON with MySQL's JSON features without errors.
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How to Change an array-valued Key in JSON Using MySQL's JSON_REPLACE and JSON_ARRAY

If you're working with JSON data in MySQL, you may encounter situations where you need to update specific fields within a JSON document. One common use-case is updating an array of values associated with a key. In this guide, we’ll address how to modify an array-valued key in a JSON field in a MySQL table using the JSON_REPLACE and JSON_ARRAY functions.

The Problem

Suppose you have a JSON field named preferences in a users table, and you wish to replace the values of an array key named religions. This task may arise while dealing with user preferences where the number of religious affiliations can vary (from 0 to 14 elements for instance). Using JSON_ARRAY_APPEND isn’t ideal because your updates may involve both additions and removals.

For example, here’s a basic idea of what your SQL update query looks like:

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

Here, the issue is how to dynamically pass a variable number of arguments into the JSON_ARRAY function.

The Solution

To correctly update your JSON array, you can follow these steps:

1. Create JSON Variables

First, define the JSON documents you want to work with. You can set a JSON variable for the religions we wish to store and another for the original JSON preferences.

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

2. Replacing Values with JSON_REPLACE

The default behavior of JSON_REPLACE treats your array as a string, which is not what we want. Instead, you need to cast it as a JSON document before using it. Here's how to do that:

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

This command will successfully update your JSON object, and the output will look like this:

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

3. Constructing the SQL Query

When you're ready to replace the value in your users table, your query would look like the following:

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

4. Testing the Output

Make sure to check that the output is in the correct format. The goal is to achieve a clean JSON where no additional quotes are added around the array:

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

Conclusion

By correctly using CAST to convert your arrays into JSON format, you'll be able to update your JSON fields without running into unwanted formatting issues. This method allows for a flexible approach that can handle varied array lengths dynamically, ensuring your SQL queries remain robust and your JSON data stays clean.

Feel free to implement these steps in your projects and enhance the way you manage JSON data within MySQL.