my first content!

src/content/journal-entries/2024-11-19.md

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+---
+title: MySQL JSON Shenanigans
+date: 2024-11-19
+---
+
+In an effort to support out-of-date installations of our app, I had to keep a JSON column in our database. The column is obsolete, as are the values within it; but these installations continue to use it. So, knowing this, I decided to put the proper values into the column. I didn't want to pollute the code of our services to do so, though. So I made it into a `GENERATED` column.
+
+I ran into two issues.
+
+First, MySQL doesn't have a way to omit `NULL` values from a JSON array.
+
+Second, the strings in the resulting array had `\u0000` interspersed between each character. This is due to how MySQL represents strings in a regular column versus how they are represented in a JSON column. I'd have to look it up, but I think I recall that by default MySQL varchars are 16-bits per character, and JSON strings are UTF-8.
+
+I "solved" the first issue by using `IF()` statements to represent all possible combinations of values. Luckily there were only 4. The only other solution I saw involved `TRIGGER`s. No, thank you.
+
+The second issue was solved by using `JSON_QUOTE()` followed by `JSON_UNQUOTE()` to remove the `\u0000` characters.
+
+```sql
+ALTER TABLE lectures
+MODIFY COLUMN vimeo_video_links JSON GENERATED ALWAYS AS (
+  IF(m3u8_url IS NOT NULL AND mp4_url IS NOT NULL,
+  JSON_ARRAY(JSON_UNQUOTE(JSON_QUOTE(m3u8_url)), JSON_UNQUOTE(JSON_QUOTE(mp4_url))),
+  IF(m3u8_url IS NOT NULL AND mp4_url IS NULL,
+    JSON_ARRAY(JSON_UNQUOTE(JSON_QUOTE(m3u8_url))),
+    IF(m3u8_url IS NULL AND mp4_url IS NOT NULL,
+      JSON_ARRAY(JSON_UNQUOTE(JSON_QUOTE(mp4_url))),
+      NULL
+    )
+  )
+  )
+) STORED;
+```