RxDB - Reactive Database for React

Why RxDB?

RxDB is more than just a state management library; it's a complete client-side database. It's built for creating offline-first applications, where the UI is rendered from a local database and synchronized with a backend. Its core is built around RxJS, a library for reactive programming, which means you can observe queries and get real-time updates in your UI as data changes.

Offline-First Architecture: Data is stored locally, making your app work seamlessly even without an internet connection. It can synchronize with any GraphQL, REST, or custom backend.
Reactive API: Queries are observable. You can subscribe to a query and the UI will automatically update when the results of that query change.
High Performance: Heavily optimized for performance, RxDB ensures your application remains fast and responsive, even with large amounts of data.
Multi-Tab Support: It synchronizes data across multiple browser tabs or windows out of the aox, providing a consistent state for the user.
Schema Support: Enforces a data schema, helping to prevent bugs and ensure data consistency.
Encryption: Supports encrypting stored data on a per-field basis, which is crucial for sensitive information.

RxDB is ideal for complex, data-heavy applications that need to work offline and reflect state changes in real-time.

Code Snippet

The following example shows how to create a database, define a schema, and insert a document. Then, it demonstrates how to subscribe to a query to get live updates.

import { createRxDatabase, addRxPlugin } from 'rxdb';
import { getRxStorageDexie } from 'rxdb/plugins/storage-dexie';
import { RxDBQueryBuilderPlugin } from 'rxdb/plugins/query-builder';
addRxPlugin(RxDBQueryBuilderPlugin);

// 1. Create a database
const myDatabase = await createRxDatabase({
  name: 'heroesdb',
  storage: getRxStorageDexie(),
});

// 2. Define a schema and create a collection
await myDatabase.addCollections({
  heroes: {
    schema: {
      title: 'hero schema',
      version: 0,
      primaryKey: 'name',
      type: 'object',
      properties: {
        name: { type: 'string', maxLength: 100 },
        color: { type: 'string' },
      },
      required: ['name', 'color'],
    },
  },
});

// 3. Insert a document
await myDatabase.heroes.insert({ name: 'Spiderman', color: 'red' });

// 4. Create an observable query and subscribe to it
const query = myDatabase.heroes.find({ selector: { color: 'red' } });
query.$.subscribe(heroes => {
  // This will log every time the result set changes
  console.log('Found heroes:', heroes);
});

Here, we set up a database and subscribe to a query for red-colored heroes. The subscription ($) is the reactive part; whenever data changes that affects this query, the callback function will re-run with the latest results.

Pros and Cons

No library is perfect; understanding the trade-offs is key to selecting the right tool.

Pros

Offline-First Capability: Robust support for offline functionality and data synchronization is a core feature, not an afterthought.
Reactive Data Queries: The observable-based API simplifies building real-time, responsive user interfaces.
Scalability: Designed to handle large amounts of data and complex queries efficiently.
Rich Feature Set: Includes encryption, multi-tab support, and schema enforcement out-of-the-box.

Cons

** steLearning Curve:** Requires understanding RxJS and reactive programming principles, which can be a hurdle for new developers.
Boilerplate: Setting up the database, schema, and collections involves more initial boilerplate than simpler state management libraries.
Bundle Size: As a full-featured database, it has a larger bundle size than lightweight state management solutions.
Complexity for Simple Cases: It can be overkill for applications with simple state management needs.

Comparison with Other State Management Libraries

The table below outlines the positioning differences between RxDB and other libraries to help you make an informed decision:

Library	Design Philosophy	Best For	Pain Points
RxDB	Reactive Client-Side Database Treats application state as a database, providing reactive queries for offline-first apps.	Data-Intensive Applications Complex, offline-first apps that need to manage and sync large datasets.	RxJS Complexity Requires a solid understanding of reactive programming and RxJS.
Zustand	Minimalist Flux-like Store A small, fast, and un-opinionated state management solution using a simple hook-based API.	Component-centric State When you need simple global state without the boilerplate of Redux.	Lack of Structure Can become disorganized in very large applications without established conventions.
TanStack Query	Server-State Manager Manages caching, refetching, and synchronization of server data, not local client state.	Managing Server Data Fetching and caching data from APIs, handling loading/error states.	Client State is Separate Not a solution for managing local UI state (e.g., form inputs, modal visibility).

Verdict: When to Adopt

Adopt RxDB when you are building a data-driven, offline-first application. If your requirements include real-time UI updates, data synchronization across multiple tabs or with a server, and the ability to handle large, structured datasets on the client, RxDB is an exceptionally powerful choice. For simpler applications that primarily manage UI state or cached server data, a lighter-weight state management library or a server-state tool like TanStack Query would be more appropriate.

TL;DR