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If the data in your app changes regularly – i.e. rows move position, get deleted, added, edited – and your app uses Relations or components like Favorites and Comments, then you need a unique value in that row that Glide can use to identify it.
Although some values are unique in certain circumstances (e.g. a person's email), the most reliable method is to use a Unique Key for each row. E.g. d5dd7e21-a940-470f-b012-a5bfa6fcb888. You could do this manually for each row (time consuming!) or if all your data is coming from a form submission you can use the Unique Identifier Special Value to populate a unique key for each entry.
However, by far the easiest way is to add the Row ID Column in the Data Editor and let Glide handle the management of your Unique Keys.
Adding the column
Most of Glide's computed columns live only in the Data Editor and don't populate your sheet. However, when you add the Row ID column in the Data Editor you also get a column in your sheet.
Glide automatically grays out this column and adds a lock symbol to remind you that it shouldn't be touched. However, you can re-order this column and the Row IDs will still work fine.
Now when you add, delete or re-order rows in your sheet, Glide will take care of this column and make sure each row has and keeps its own Unique ID.
When you use the Row ID column components like Comments and Favorite will no longer ask you for a 'Key' or a 'Topic' – instead they will automatically use the Row ID column to locate a row.