RealmAndroidDemo

Realm Android Demo Project

This project explains how to initialize and use Realm database for Android platform. Also it shows how to alter a existing table.

#Version 0

Your Model class for Book public class Book extends RealmObject{

@PrimaryKey
private int id;
private String title;
private String author;

...getters and setters

}

Your application Class public class MyApplication extends Application {

@Override
public void onCreate() {
    super.onCreate();
    Realm.init(this);

    //Realm Schema Version 0
    RealmConfiguration configuration = new RealmConfiguration.Builder().
            name(Realm.DEFAULT_REALM_NAME)
            .schemaVersion(0)
            .build();
}

}

Adding a New Book into database

Realm realm = Realm.getDefaultInstance(); realm.beginTransaction(); realm.insert(book); realm.commitTransaction();

Retrieve all the books from the database

public RealmResults getBooks(){ return realm.where(Book.class).findAll(); }

#Version 1

Now we are going to add new fiedl "cost" to the Book class. Then we need to migrate the database

public class Book extends RealmObject{

@PrimaryKey
private int id;
private String title;
private String author;

//newly added field
private int cost;

    ...getters and setters

}

Then need to implement migration class

public class MyMigration implements RealmMigration {

@Override
public void migrate(DynamicRealm realm, long oldVersion, long newVersion) {
    RealmSchema realmSchema = realm.getSchema();
    if(oldVersion == 0){
        //adding new column Cost
        RealmObjectSchema bookSchema = realmSchema.get("Book");
        bookSchema.addField("cost",int.class, FieldAttribute.REQUIRED);
        bookSchema.transform(new RealmObjectSchema.Function() {
            @Override
            public void apply(DynamicRealmObject obj) {
                //initializing cost by 0 for existing rows
                obj.setInt("cost",0);
            }
        });
    }
}

}

Then do the necesary changes in Application java file

public class MyApplication extends Application { @Override public void onCreate() { super.onCreate();

    Realm.init(this);
    //Realm Schema Version 1 (adding new field cost)
    RealmConfiguration configuration = new RealmConfiguration.Builder().
            name(Realm.DEFAULT_REALM_NAME)
            .schemaVersion(1)
            .migration(new MyMigration())
            .build();
    Realm.setDefaultConfiguration(configuration);
}

}