ObjectBox vs RxDB

ObjectBox is an embedded, object-oriented NoSQL database for mobile applications and IoT devices. Its database provides native object APIs, relationships, reactive observers, ACID transactions and automatic schema migration. ObjectBox Sync can move data between devices and a backend or server, including for offline-first use cases. Listed language APIs include Java, Kotlin, Swift, Flutter/Dart, Go, Python and C/C++. The product supports vector search, with no embedding-column dimension limit stated in its FAQ. ObjectBox says it supports direct synchronization to MongoDB; connectors for other backend databases may require custom development. Its Sync Server can be self-hosted on POSIX systems and cloud providers, though ObjectBox does not currently provide cloud hosting. The core database plan is free; Sync pricing is quoted per project based on needs. The company describes its focus as mobile and IoT development, particularly decentralized systems with restricted devices and offline scenarios. Mesh Sync is available for Android Java/Kotlin and Flutter/Dart starting with version 6.0.0-beta, with APIs that may change before final release.

RxDB is a NoSQL database for JavaScript that runs inside an application and keeps data locally on the client. It supports offline operation, including applications that run entirely without a backend. When synchronization is needed, its Sync Engine connects to backends including RxServer, GraphQL, Firebase, Supabase, MongoDB, NATS, HTTP, CouchDB, WebRTC, Appwrite, Google Drive, and Microsoft OneDrive. Observable queries update as stored data changes. RxDB runs in browsers, mobile apps, desktop applications, and servers, with storage options including LocalStorage, IndexedDB, OPFS, SQLite, Node.js Filesystem, Expo Filesystem, MongoDB, and FoundationDB, among others. Collections use JSON Schema with validation and migration support. An encryption plugin protects locally stored documents with a password in browsers, React Native, and Node.js. The free tier is under Apache 2.0 and allows up to 13 open collections in parallel. Free users get community support through GitHub and Discord; Enterprise includes an SLA with a 24-hour first response. Pro costs $99 a month billed annually, and Pro Plus costs $239 a month billed annually.