So I'm working on a project which has been published to users. Before I put my hand on this project, this project has an 1.0 and an 2.0 version, v2.0 modified the data model of core data, but the one who did this didn't add a new version to data model.
So when user upgrade from v1.0 to v2.0, it will crash.
My problem is now I'm deploying v3.0, how do I modify my xcdatamodel so that user with v1.0 and v2.0 can both upgrade to v3.0 without problem?
Get the V1 model and add a new version to it that is identical to v2 and then add another V3 model to that so that you end up with a model that has all three versions. That way you should be able to use lightweight migration from either of the previous versions, assuming that your model changes will in fact support lightweight migration. If not then do a manual migration as suggested by @Mundi. You can recover the V1 model from the V1 app bundle if you no longer have the source code but you do need a copy of the V1 app bundle to do so. You might have to google for how to do this or let me know and I will hunt around as I will have it documented somewhere... Hope this helps.