Realm. How to migrate with Date from outer class

Question

Now I have a schema like this:

class Entries {
 String name;
 Date date;
 RealmList<Entry> entries;
}

class Entry {
 int id;
 int hours;
 int minutes;
}

And now i need migrate to schema like this:

class Entry {
 int id;
 Date date;
}

So i need to take a date from Entries class, and set it to each Entry in list and set a hours and minutes from existing fields.

How I can do this via migration?

Answer 1

Specifically you need to write following code (or something very similar):

public class Migration implements RealmMigration {
    @Override
    public void migrate(final DynamicRealm realm, long oldVersion, long newVersion) {
        RealmSchema schema = realm.getSchema();
        // Migrate from version 0 to version 1
        if (oldVersion == 0) {
            RealmObjectSchema entriesSchema = schema.get("Entries");
            RealmObjectSchema entrySchema = schema.get("Entry");

            entrySchema.addField("date", Date.class);

            Calendar calendar = Calendar.getInstance();
            RealmResults<DynamicRealmObject> entriesList = realm.where("Entries").findAll();
            for (DynamicRealmObject entries : entriesList) {
                RealmList<DynamicRealmObject> entryList = entry.getList("entries");
                for (DynamicRealmObject entry : entryList) {
                    Date date = entries.getDate("date");
                    calendar.setTime(date);
                    calendar.set(Calendar.HOUR_OF_DAY, entry.getInt("hours"));
                    calendar.set(Calendar.MINUTES, entry.getInt("minutes");
                    entry.setDate("date", calendar.getTime());
                }
            }
            entrySchema.removeField("hours");
            entrySchema.removeField("minutes");
            oldVersion++;
        }
    }

    // hashCode, equals
}