Realm is a mobile database: a replacement for SQLite & ORMs
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Realm is a mobile database that runs directly inside phones, tablets or wearables. This repository holds the source code for the Java version of Realm, which currently runs only on Android.


  • Mobile-first: Realm is the first database built from the ground up to run directly inside phones, tablets and wearables.
  • Simple: Data is directly exposed as objects and queryable by code, removing the need for ORM's riddled with performance & maintenance issues. Plus, we've worked hard to keep our API down to very few classes: most of our users pick it up intuitively, getting simple apps up & running in minutes.
  • Modern: Realm supports easy thread-safety, relationships & encryption.
  • Fast: Realm is faster than even raw SQLite on common operations, while maintaining an extremely rich feature set.

Getting Started

Please see the detailed instructions in our docs to add Realm to your project.


Documentation for Realm can be found at The API reference is located at

Getting Help

  • Need help with your code?: Look for previous questions on the #realm tag — or ask a new question. We activtely monitor & answer questions on SO!
  • Have a bug to report? Open an issue. If possible, include the version of Realm, a full log, the Realm file, and a project that shows the issue.
  • Have a feature request? Open an issue. Tell us what the feature should do, and why you want the feature.
  • Sign up for our Community Newsletter to get regular tips, learn about other use-cases and get alerted of blogposts and tutorials about Realm.

Using Snapshots

If you want to test recent bugfixes or features that have not been packaged in an official release yet, you can use a -SNAPSHOT release of the current development version of Realm via Gradle, available on OJO

buildscript {
    repositories {
        maven {
            url ''
    dependencies {
        classpath "io.realm:realm-gradle-plugin:<version>-SNAPSHOT"

allprojects {
    repositories {
        maven {
            url ''

See version.txt for the latest version number.

Building Realm

In case you don't want to use the precompiled version, you can build Realm yourself from source.


  • Download the JDK 7 or JDK 8 from Oracle and install it.
  • Download & install the Android SDK Build-Tools 24.0.0, Android N (API 24) (for example through Android Studio’s Android SDK Manager).
  • Install CMake from SDK manager in Android Studio ("SDK Tools" -> "CMake").

  • Realm currently requires version r10e of the NDK. Download the one appropriate for your development platform, from the NDK archive. You may unzip the file wherever you choose. For OSX, a suggested location is ~/Library/Android. The download will unzip as the directory android-ndk-r10e.

  • If you will be building with Android Studio, you will need to tell it to use the correct NDK. To do this, define the variable ndk.dir in realm/ and assign it the full path name of the directory that you unzipped above. Note that there is a local.properites in the root directory that is not the one that needs to be edited.

  • Add two environment variables to your profile (presuming you installed the NDK in ~/Library/android-ndk-r10e):

    export ANDROID_HOME=~/Library/Android/sdk
    export ANDROID_NDK_HOME=~/Library/Android/android-ndk-r10e
  • If you will be launching Android Studio from the OS X Finder, you should also run the following two commands:

    launchctl setenv ANDROID_HOME "$ANDROID_HOME"
    launchctl setenv ANDROID_NDK_HOME "$ANDROID_NDK_HOME"
  • If you'd like to specify the location in which to store the archives of Realm Core, define the REALM_CORE_DOWNLOAD_DIR environment variable. It enables you to keep Core's archive when executing git clean -xfd.

    export REALM_CORE_DOWNLOAD_DIR=~/.realmCore

    OS X users must also run the following command in order for Android Studio to see this environment variable..


It would be a good idea to add all of the symbol definitions (and their accompanying launchctl commands, if you are using OS X) to your ~/.profile (or ~/.zprofile if the login shell is zsh)

Download sources

You can download the source code of Realm Java by using git. Since realm-java has git submodules, use --recursive when cloning the repository.

git clone --recursive


git clone --recursive


Once you have completed all the pre-requisites building Realm is done with a simple command

./gradlew assemble

That command will generate:

  • a jar file for the Realm Gradle plugin
  • an aar file for the Realm library
  • a jar file for the annotations
  • a jar file for the annotations processor

The full build may take an hour or more, to complete.

Other Commands

  • ./gradlew tasks will show all the available tasks
  • ./gradlew javadoc will generate the Javadocs
  • ./gradlew monkeyExamples will run the monkey tests on all the examples
  • ./gradlew installRealmJava will install the Realm library and plugin to mavenLocal()
  • ./gradlew clean -PdontCleanJniFiles will remove all generated files except for JNI related files. This reduces recompilation time a lot.
  • ./gradlew connectedUnitTests -PbuildTargetABIs=$(adb shell getprop ro.product.cpu.abi) will build JNI files only for the ABI which corresponds to the connected device. These tests require a running Object Server (see below)

Generating the Javadoc using the command above may generate warnings. The Javadoc is generated despite the warnings.


The repository is organized in six Gradle projects:

  • realm: it contains the actual library (including the JNI layer) and the annotations processor.
  • realm-annotations: it contains the annotations defined by Realm.
  • realm-transformer: it contains the bytecode transformer.
  • gradle-plugin: it contains the Gradle plugin.
  • examples: it contains the example projects. This project directly depends on gradle-plugin which adds a dependency to the artifacts produced by realm.
  • The root folder is another Gradle project. All it does is orchestrate the other jobs

This means that ./gradlew clean and ./gradlew cleanExamples will fail if assembleExamples has not been executed first. Note that IntelliJ does not support multiple projects in the same window so each of the six Gradle projects must be imported as a separate IntelliJ project.

Since the repository contains several completely independent Gradle projects, several independent builds are run to assemble it. Seeing a line like: :realm:realm-library:compileBaseDebugAndroidTestSources UP-TO-DATE in the build log does not imply that you can run ./gradlew :realm:realm-library:compileBaseDebugAndroidTestSources.


The ./examples folder contain a number of example projects showing how Realm can be used. If this is the first time you checkout or pull a new version of this repository to try the examples, you must call ./gradlew installRealmJava from the top-level directory first. Otherwise the examples will not compile as they depend on all Realm artifacts being installed in mavenLocal().

Standalone examples can be downloaded from website.

Running Tests on a Device

To run these tests you must have a device connected to the build computer and the adb command must be in your PATH

  1. Connect an Android device and verify that that the command adb devices shows a connected device:

    adb devices
    List of devices attached
    004c03eb5615429f    device
  2. Run instrumentation tests:

    cd realm
    ./gradlew connectedBaseDebugAndroidTest

These tests may take as much as half an hour to complete.

Running Tests Using The Realm Object Server

Tests in realm/realm-library/src/syncIntegrationTest require a running testing server to work. A docker image can be built from tools/sync_test_server/Dockerfile to run the test server. tools/sync_test_server/ will build the docker image automatically.

To run a testing server locally:

  1. Install docker.

  2. Run tools/sync_test_server/

    cd tools/sync_test_server

    This command will not complete until the server has stopped.

  3. Run instrumentation tests

    In a new terminal window, run:

    cd realm
    ./gradlew connectedObjectServerDebugAndroidTest

Note that if using VirtualBox (Genymotion), the network needs to be bridged for the tests to work. This is done in VirtualBox > Network. Set "Adapter 2" to "Bridged Adapter".

These tests may take as much as half an hour to complete.


See for more details!

This project adheres to the Contributor Covenant Code of Conduct. By participating, you are expected to uphold this code. Please report unacceptable behavior to

The directory realm/config/studio contains lint and style files recommended for project code. Import them from Android Studio with Android Studio > Preferences... > Code Style > Manage... > Import, or Android Studio > Preferences... > Inspections > Manage... > Import. Once imported select the style/lint in the drop-down to the left of the Manage... button.


Realm Java is published under the Apache 2.0 license. The underlying core is available under the Realm Core Binary License while we work to open-source it under the Apache 2.0 license.

This product is not being made available to any person located in Cuba, Iran, North Korea, Sudan, Syria or the Crimea region, or to any other person that is not eligible to receive the product under U.S. law.


If you use Realm and are happy with it, all we ask is that you please consider sending out a tweet mentioning @realm, announce your app on our mailing-list, or email to let us know about it!

And if you don't like it, please let us know what you would like improved, so we can fix it!