How to Update Realm SDK Database Schema for Android
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This is a follow-up article in the Getting Started Series.
In this article, we learn how to modify/migrate Realm local database schema.
As you add and change application features, you need to modify database schema, and the need for migrations arises, which is very important for a seamless user experience.
By the end of this article, you will learn:
- How to update database schema post-production release on play store.
- How to migrate user data from one schema to another.
Before we get down to business, let's quickly recap how we set
Realm in our application.
Doing migration in Realm is very straightforward and simple. The high-level steps for the successful migration of any database are:
- Update the database version.
- Make changes to the database schema.
- Migrate user data from old schema to new.
This is the simplest step, which can be done by incrementing the version of
REALM_SCHEMA_VERSION, which notifies Relam about database changes. This, in turn, runs triggers migration, if provided.To add migration, we use the
migration function available in RealmConfiguration.Builder, which takes an argument of RealmMigration, which we will review in the next step.In
Realm, all the migration-related operation has to be performed within the scope
of RealmMigration.To add/update/rename any field:
All the data transformation during migration can be done with
transform function with the help of set and get methods.In the above snippet, we are setting the default value of fullName by extracting the value from old data, like firstName and lastName.
We can also use
transform to update the data type.In case you want to delete the complete
Realm, you can use deleteRealmIfMigrationNeeded with RealmConfiguration.Builder, but that should be considered as the last resort.Thank you for reading! If you have any queries or comments, you can share them on
the Realm forum or tweet
me @codeWithMohit.
In the next article, we will discuss how to migrate the Realm database with Atlas Device Sync.
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