Android Working with Realm Database — Replacing SQLite & Core Data

What is Realm?

Realm is a mobile database and a replacement for SQLite. Although is an OO database it has some differences with other databases. Realm is not using SQLite as it’s engine. Instead it has own C++ core and aims to provide a mobile-first alternative to SQLite. Realm store data in a universal, table-based format by a C++ core. This is what allows Realm to allow data access from multiple languages as well as a range of ad hoc queries.

Below are the advantages of Realm over SQLite:
> faster than SQLite (up to 10x speed up over raw SQLite for normal operations)
> easy to use
> object conversion handled for you
> convenient for creating and storing data on the fly
> very responsive team

Also there are some disadvantages which might be taken into consideration:
> no importing
> still under active development
> not a lot of content online
> can’t access objects across threads

Realm at the moment is missing the following features:
> null support
> auto incrementing id’s
> Map support
> easy migrations
> notifications on specific data changed
> compound primary keys

Prerequisites:

• Realm is supported in Android only, not available for Java at the moment.
• Android Studio version 0.8.6
• JDK version 7
• Android API Level minimum 9 (Android 2.3 Gingerbread)

Installation

Add compile ‘io.realm:realm-android:0.83.0+’ in your build.gradle and sync a project. Or, you can download a realm-VERSION.jar and add it into app/libs.

Models

If you want a class to be stored in Realm, it should extend from RealmObject. Realm supports the following field types: boolean, byte, short, ìnt, long, float, double, String, Date. Moreover, subclasses of RealmObject and RealmList<? extends RealmObject> support model relationships.
The boxed types Boolean, Byte, Short, Integer, Long, Float, and Double can also be used in model classes. With their help, you can set the value of a field to null.

Annotations

@Required — tells Realm to enforce checks that disallow null values.
@Ignore — supposes that a field should not be persisted to disk.
@Index — will add a search index to the field. Due to this queries will be faster, although inserts will become slower and the data file will get larger.
@PrimaryKey — supposes that the field is indexed.

Start Using Realm

Initialize Realm in Application:

public class MyApplication extends Application {
@Override
public void onCreate() {
super.onCreate();
RealmConfiguration config = new 
RealmConfiguration.Builder(context).build();
Realm.setDefaultConfiguration(config);
}
}

Initialize Realm in Activity:

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Realm realm = Realm.getDefaultInstance();
}
}

Writing in the Database

If you want to write something in the database you just need to call:

Realm realm = Realm.getInstance(this);
realm.beginTransaction();
//... add or update objects here ...
realm.commitTransaction();

You always have an opportunity to cancel your transactions, just call:

realm.cancelTransaction();

Creating Objects-( University)

If you want to save an object in the Realm database, the class of that object should extend RealmObject

public class University extends RealmObject {
@PrimaryKey
private String id;
@Required
private String name;
private RealmList students;
// getters and setters
}

University will be able to add a university, delete a university by id, get a university by id from the database, etc

Adding Data in University

Realm realm = Realm.getInstance(SimpleRealmApp.getInstance());
realm.beginTransaction();
University u = realm.createObject(University.class);
u.setId(UUID.randomUUID().toString());
u.setName(university.getName());
realm.commitTransaction();

Deleting Data from University

Realm realm = Realm.getInstance(SimpleRealmApp.getInstance());
realm.beginTransaction();
University university = realm.where(University.class).equalTo(RealmTable.ID, Id).findFirst();
university.removeFromRealm();
realm.commitTransaction();

Get All University data

Realm realm = Realm.getInstance(SimpleRealmApp.getInstance());
RealmQuery query = realm.where(University.class);
RealmResults results = query.findAll();

References

Realm for Android

Streamlining Mobile App Databases with Realm.io

realm/realm-java