Migrating from Realm Cloud to Mongodb Realm without losing offline data

[Jay (Jason Wooten)]

@Arnaud_Combes

Is there a way to know if all the data have been uploaded to Realm Cloud before performing the migration?

There is not. If a user was working offline the last time the used the app, that data would not have been sync’d but there’s no way to know that, unless you accounted for it programmatically in some way.

@Arnaud_Combes

With Realm Cloud, local data is stored in a * .realm file. But what about MongoDB Realm ? Will it replace/delete the .realm file or will it create a new file ? If the .realm file still exists, I plan to transfer it on a storage server in case offline data was not synchronized during the migration, so I could always get them back.

Several parts to that question.

• MongoDB Realm uses partitions to store it’s data in ‘Realms’, each partition will be a different local realm File. For example an Object whose partition key (a Realm in MongoDB Realm) is Task Tracker will have a local file name of %22Task%20Tracker%22 . Additionally the path to the file stored on the device will be different.
• It will not delete the existing *.realm file as new files are created to handle the new realm partitions

@Arnaud_Combes

MongoDB Realm sync is still in beta, when will it no longer be ? When Realm Cloud will be closed, will it work ? Do I have to wait before migrating? Because sync is essential for my app.

A Mongo employee can address those questions but you should begin the migration now and not wait.

Keep in mind that there are a number of differences between Realm Cloud and MongoDB Realm, including adding _id and partition properties to you objects. There’s a whole thread on the process that you should definitely review. See Migrating from Legacy Realm Sync to MongoDB Realm Guide