1. What is it and why is it needed?

Realm Kotlin is a modern, fast, and object-oriented mobile database created specifically for the Kotlin Multiplatform (KMP) ecosystem. Unlike traditional solutions such as SQLite or Room, Realm works not with tables and rows, but directly with Kotlin objects. This means you work with data just like with regular classes, without needing to write SQL queries or map data manually. Realm Kotlin is the direct successor to the popular Realm library for Java, but completely rewritten from scratch for Kotlin, supporting coroutines, Flow, and multiplatform (Android, iOS, macOS, JVM).

Why is it needed? Primarily, to speed up mobile application development. Realm allows you to reduce the amount of boilerplate code when working with local storage. You simply declare a data model, and Realm automatically generates everything needed for saving, reading, updating, and deleting objects. Thanks to built-in support for reactive streams (Flow from the kotlinx.coroutines library), any changes in the database are instantly reflected in the UI, which is ideal for the MVVM architecture. Realm is also known for its high performance: it runs on its own C++ engine, providing read and write speeds close to native.

Main use cases: caching data from the server, working in offline mode, storing complex nested structures (e.g., an online store cart or chat history), synchronizing data between devices via Realm Sync (MongoDB Atlas cloud service). Realm Kotlin is not just "another ORM", it is a full-fledged database engine that changes the approach to state management in an application.

2. Installation

Realm Kotlin is installed via the Gradle build system. Since the library targets Kotlin Multiplatform, the configuration differs slightly from standard Android dependencies.

Important: Realm Kotlin is not installed via pip (Python) or npm (JavaScript). It is a native library for JVM/Android/iOS.

Add the following code to your root build.gradle.kts file (Project-level):

// Root build.gradle.kts\nplugins {\n    id("io.realm.kotlin") version "1.16.0" apply false\n}

Then in the build.gradle.kts file of your module (app or shared):

// Module build.gradle.kts\nplugins {\n    kotlin("multiplatform")\n    id("io.realm.kotlin")\n}\n\nkotlin {\n    // Target configuration (Android, iOS, etc.)\n    androidTarget()\n    listOf(\n        iosX64(),\n        iosArm64(),\n        iosSimulatorArm64()\n    ).forEach {\n        it.binaries.framework {\n            baseName = "shared"\n        }\n    }\n\n    sourceSets {\n        val commonMain by getting {\n            dependencies {\n                implementation("io.realm.kotlin:library-base:1.16.0")\n                // For coroutine support\n                implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.8.0")\n            }\n        }\n        // ... other source sets\n    }\n}

For a pure Android project (without KMP), the configuration is simpler:

// build.gradle.kts (Module :app)\nplugins {\n    id("com.android.application")\n    kotlin("android")\n    id("io.realm.kotlin")\n}\n\nandroid {\n    // ... standard settings\n}\n\ndependencies {\n    implementation("io.realm.kotlin:library-base:1.16.0")\n}

After Gradle sync, the library is ready to use.

3. Quick Start — Minimal Working