Realm with pre populated data into assets?

Question

Normally I use Realm as:

RealmConfiguration config = new RealmConfiguration.Builder(applicationContext).deleteRealmIfMigrationNeeded().build();

How can I add to the assets folder of my project a database with data and read it?

Answer 1

Since Realm Java 0.91.0 there has been an assetFile(String) option on the RealmConfiguration that automatically will copy a file from assets and use that if needed (e.g. if the Realm is opened the first time or has been deleted for some reason):

RealmConfiguration config = new RealmConfiguration.Builder()
  .assetFile("path/to/file/in/assets") // e.g "default.realm" or "lib/data.realm"
  .deleteRealmIfMigrationNeeded()
  .build()

The above will copy the file from assets the first time the Realm is opened or if it has been deleted due to migrations (remember to update the asset Realm in that case).

---

OLD ANSWER:

It is possible to bundle a Realm database in the assets folder, but then you just need to copy it from there when starting the app the first time.

We have an example of how to copy the files here: https://github.com/realm/realm-java/blob/master/examples/migrationExample/src/main/java/io/realm/examples/realmmigrationexample/MigrationExampleActivity.java#L101-Lundefined

copyBundledRealmFile(this.getResources().openRawResource(R.raw.default_realm), "default.realm");

private String copyBundledRealmFile(InputStream inputStream, String outFileName) {
    try {
        File file = new File(this.getFilesDir(), outFileName);
        FileOutputStream outputStream = new FileOutputStream(file);
        byte[] buf = new byte[1024];
        int bytesRead;
        while ((bytesRead = inputStream.read(buf)) > 0) {
            outputStream.write(buf, 0, bytesRead);
        }
        outputStream.close();
        return file.getAbsolutePath();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

Answer 2

Since Realm 0.89.0 RealmConfiguration.initialData(Realm.Transaction) can now be used to populate a Realm file before it is used for the first time.

RealmConfiguration conf = new RealmConfiguration.Builder(context)
.initialData(new Realm.Transaction() {
                @Override
                public void execute(Realm realm) {
                  realm.beginTransaction();
                  realm.createObject(....)
                  realm.commitTransaction();
                }
            }).deleteRealmIfMigrationNeeded().name("mRealm.db").build();
Realm realm = Realm.getInstance(conf);