A Technical Audit of RealmDB and ObjectBox

If you’re migrating from RealmDB to ObjectBox: most concepts map cleanly (entities/models, queries, indexes, relationships, CRUD, and optional sync). The main shift is that ObjectBox keeps your model classes “plain” and makes reactivity and sync explicit choices rather than implicit defaults. Once you internalize a few conceptual differences, the migration is typically straightforward - and many teams end up preferring the extra control.

Foundational Architecture & Data Modeling

The architectural foundation of a database determines its performance characteristics as well as the developer experience, schema evolution capabilities, and the degree of coupling it imposes on an application. An audit of RealmDB and ObjectBox shows two common object-database approaches to mapping code to storage: RealmDB uses an inheritance-based managed object model, while ObjectBox uses annotations to keep entities as plain objects. [MongoDB Realm Swift Docs | ObjectBox Docs]

1.1 RealmDB: The Integrated Object Model

RealmDB's approach to data modeling is to directly map language-native classes to the database schema, a concept it promotes as intuitive for developers. Persistable objects are defined by creating classes that inherit from a base Realm.Object class, making them "managed objects" tightly coupled to the Realm instance. This pattern is consistent across its various SDKs. [MongoDB Realm Swift Docs]

For instance, the official Swift documentation provides a canonical example where a Dog class is made persistable by inheriting from Object and using the @Persisted property wrapper to mark fields for storage:

// Define your models like regular Swift classes
class Dog: Object {
    @Persisted var name: String
    @Persisted var age: Int
}