I'm archiving this repro as 1) Realm is now deprecated by MongoDB, but equally importantly, 2) this functionality was built into the Realm Android SDK at some stage.

I hope this was useful to a few of you!

Android Realm Asset Helper

A small library of methods to help with Realm.IO integration in Android apps

Copies a realm database from a the assets folder. Efficienty handles versioning of read-only realm databases.

About

Motivated by direct support for read-only databases in iOS app bundles and modelled on ideas in Android SQLite Assset Helper, the goal of this library is to help with some common tasks found with using Realm.io in Android. It is actively maintained and used by Egghead Games for their Andriod & iOS brain puzzle apps.

Features

copy the realm db from the app bundle and return filename ready to be opened
easy, efficient updating of read-only databases

Simplest Example

In this simplest scenario, the library handles locating and copying the realm file from your apk into the Android file system so it is ready to use.

Say your app has a single Realm database that ships with some sample data. You need to copy that database on first install so it is ready to use in your app. Store your file called, say, appdata.realm in your assets/data folder and include code like this:

import com.eggheadgames.realmassethelper;

Realm realm;

RealmAssetHelper.getInstance(context).loadDatabaseToStorage("data", "appdata", new IRealmAssetHelperStorageListener() {
    @Override
    public void onLoadedToStorage(String realmDbName, RealmAssetHelperStatus status) {
                realmConfig = new RealmConfiguration.Builder(context)
                        .name(realmDbName)
                        .build();
                realm = Realm.getInstance(realmConfig);
            }
    }
});

This will:

find appdata.realm in assets/data folder
see if there is an existing appdata.realm already installed
copy the appdata.realm from assets/data only if no pre-existing file is found
return the realm file name and status

Read-only Data Example

Another scenario is where you include a large amount of data to use read-only in your application, such as product catalogue information or game level data.

Say you have the 3rd version of your company's products.realm database to ship with your latest apk. Store it in assets/data with the name products_3.realm, then load it with:

RealmAssetHelper.getInstance(context).loadDatabaseToStorage("data", "products", new IRealmAssetHelperStorageListener() {
    @Override
    public void onLoadedToStorage(String realmDbName, RealmAssetHelperStatus status) {
                realmConfig = new RealmConfiguration.Builder(context)
                        .name(realmDbName)
                        .build();
                realm = Realm.getInstance(realmConfig);
            }
    }
});

This will:

find the products_3.realm in assets/data folder
see if there is an existing products.realm installed and check a sharedPreference value to see what version it is
copy the realm data if it is newer (removing the _3)
return the realm file name and status

Installation Instructions

Add the JitPack.io repository to your root build.gradle:

allprojects {
    repositories {
        maven { url "https://jitpack.io" }
    }
}

Add a dependency to your application related build.gradle

dependencies {
    compile 'com.github.eggheadgames:android-realm-asset-helper:2.1.0'
}

Explanation

It can be convenient to have a read-only database as part of an apk. This might have game level information, for example, or other data like zip codes or product information. If the app treats it as "read-only" (perhaps also using a separate realm database for storing other state data), then data updates are as simple as updating the "master" realm file in the apk and then copying it over on first run after the user updates.

iOS note: This is conceptually simpler in iOS, because realm can access read-only data directly from the application bundle (= apk). This library was originally created so that our iOS and Android apps could share the same read-only realm database.

This helper library adds support for this "read-only data included in apk" scenario.

For efficiency, the copy should only be made when the database has changed. This is handled as follows:

if no copy of the database exists, it is copied
if a copy exists, then a sharedPreference value is checked to see what database version it is (defaults to 0 if not found)
the APK assets folder is searched for the database name with a postfix _NN in the name (e.g. products_12). If the NN value is higher than the current version, then the new database is copied (with the _NN removed) and the sharedPreference value is updated
if no database is found in assets, this causes an immediate error (as this is usually an oversight and should be resolved ASAP)

Thus, the workflow for an apk with read-only data becomes:

store the database, e.g. products in assets with the name products_0
when products is updated, rename the fie from products_0 to products_1

The helper will see the change and copy the database as needed.

Caveats

There is no consideration given (so far) to database migration requirements or any sort of "update my user's existing realm database from this new realm database". That is clearly a useful enhancement to think about for the future but was beyond the scope of the initial release.

Pull Requests, Issues, Feedback

We welcome pull requests. If you have questions or bugs, please open an issue and we'll respond promptly.