I am upgrading to Capacitor 3 and I’m using the Storage API. My app already had some data stored locally but after upgrading I find the data is not able to be read. I can see the data in Chrome Devtools.
So I guess I need to use Storage.migrate() ?
What I’m not sure about is where to use it and how to use it just the once… or do I just keep calling it forevermore (doesn’t seem right)?
Writing that out now gets me thinking that it’ll be tied in with my app versions, is that the normal approach?
Did you ever figure this out? I was wondering the same thing myself.
I already had an internal database version in the store so I’m going to bump that and have a hardcoded check for the older version.
I tried using getInfo() from Capacitor’s App API but it is not ‘Not implemented on web’. So, if you’re developing an app but using a browser for development this won’t work. It is possible appVersion might work in the browser but I haven’t tried it.
It might be that you don’t need to add a check at all, and migrate() does the check for you because it obviously knows the format of the data, but no-one from the ionic or capacitor teams responded to my query, and the docs don’t say either, so who knows!?
I will try it out this week. Let me know how you get on.
This clearly isn’t going to work because the db version is stored… using storage from Capacitor v2!! 
I could use localstorage.getItem(‘_cap_myKey’) in the browser to read the v2 data but I don’t know if that works in Android or iOS.
So I’ve had a look a the code in node_modules/@capacitor/storage/dist/plugin.js and it seems as though the prefix has changed between versions. The code checks for any keys stored using the old prefix (_cap_), and then, if old keys were found, writes out new keys with the new/current prefix.
As that is all it seems to do it’s probably quite safe to include migrate() in your app on startup forevermore.
I hope that helps.
While I haven’t tried it myself, there’s the migrate function. Usually, you would call migrate once upon app startup. Then going forward, use the Storage API as you currently are (since I believe the API didn’t change between v2 and v3).
You could leave that code in place forever, or remove it in a future app version once you’re comfortable enough that users have all been updated.