Discussion on NoSql Databases that can be used in android development. The talk discusses both firebase and realm databases and how one might wanna use them .

1. NoSQL databases
Sometimes being unstructured helps
Amrit Sanjeev
Organizer @ Blrdroid

2. Who am I ?

3. Agenda
● Type of databases available in Android
● When to use them
● How they help ?
● Some feature of popular db products

4. Data trends
- Amount of data stored is increasing
- Data is more unstructured
- Efficiency and performance are critical
- Relations are more complex

5. Datastore evolution

6. RDBMS vs NoSQL
- Structured data
- Transform data policy
- Atomic transactions
- Data model != Entity model
- Scale up
- Semi or unstructured data
- Update schema policy
- Eventual consistency
- Data model ~= Entity model
- Scale out

8. Real time database
- NoSQL, JSON database
- Maps each piece of data to a URL
- Offline support
- Supports iOS , Android and Web
- Pushes updates in milliseconds when
things change

9. Cross platform support

10. Listening to data changes
● Attach an asynchronous listener to a Firebase reference.
● The listener will be triggered
○ once for the initial state of the data
○ again anytime the data changes
Firebase ref = new Firebase("https://docs-examples.firebaseio.com/web/saving-data/fireblog/posts");
ref.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot snapshot) {
System.out.println(snapshot.getValue());
}
@Override
public void onCancelled(FirebaseError firebaseError) {
System.out.println("The read failed: " + firebaseError.getMessage());
}
});

11. Reading data once
● Callback will be called only once
● removed after the first trigger
Firebase ref = new Firebase("https://docs-examples.firebaseio.com/web/saving-data/fireblog/posts");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot snapshot) {
// do some stuff once
}
@Override
public void onCancelled(FirebaseError firebaseError) {
}
});

12. Querying data
● Selectively retrieve data based on various factors.
● Start by specifying how you want your data to be ordered
○ orderByChild()
○ orderByKey()
○ orderByValue()
○ orderByPriority()
● combine these other methods to conduct complex queries
○ limitToFirst()
○ limitToLast()
○ startAt()
○ endAt()
○ equalTo()

14. What is Realm ?
- Zero copy object store database
- Easy setup
- Optimized for read , not writes
- Cross platform
- Simple Querying interface

15. Defining objects in realm
public class Person extends RealmObject {
@PrimaryKey
private long id;
private String name;
private RealmList<Dog> dogs;
// Declare one-to-many relationships
// ... Generated getters and setters ...
}
@RealmClass
public class Person implements RealmModel {
@PrimaryKey
private long id;
private String name;
private RealmList<Dog> dogs;
// Declare one-to-many relationships
// ... Generated getters and setters ...
}

16. Relationships
public class Person extends RealmObject {
private String firstName;
private String lastName;
private Dog dog;
// ... Generated getters and setters ...
}
public class Person extends RealmObject {
private String firstName;
private String lastName;
private RealmList<Dog> dogs;
// ... Generated getters and setters ...
}
public class Person extends RealmObject {
private String firstName;
private String lastName;
private RealmList<Person> friends;
// .. getters/setters
}

17. Saving objects in realm
// Use them like regular java objects
Dog dog = new Dog();
dog.setName("Rex");
dog.setAge("1");
// Get a Realm instance
Realm realm = Realm.getDefaultInstance();
// Persist your data easily
realm.beginTransaction();
realm.copyToRealm(dog);
realm.commitTransaction();
// Get a Realm instance
Realm realm = Realm.getDefaultInstance();
// Create and persist your data easily
realm.beginTransaction();
Dog dog = realm.createObject(Dog.class);
dog.setName("Rex");
dog.setAge("1");
realm.commitTransaction();

18. Transactions
try {
realm.beginTransaction();
Dog dog = realm.where(Dog.class).
equalTo("name", "Fido").findFirst();
dog.setAge(15);
realm.commitTransaction();
}
catch (Exception ex) {
// rollback
realm.cancelTransaction();
}
realm.executeTransaction(
new Realm.Transaction() {
@Override
public void execute(Realm realm) {
Dog dog= realm.where(Dog.class).
equalTo("name", "Fido").findFirst();
dog.setAge(15);
}
})

19. Async Transactions
// Use them like regular java objects
realm.executeTransactionAsync(new Realm.Transaction() {
@Override
public void execute(Realm bgRealm) {
User user = bgRealm.createObject(User.class);
user.setName("John");
}
}, new Realm.Transaction.OnSuccess() {
@Override
public void onSuccess() {
// Transaction was a success.
}
}, new Realm.Transaction.OnError() {
@Override
public void onError(Throwable error) {
// Transaction failed and was automatically canceled.
}
});
RealmAsyncTask transaction = realm.executeTransactionAsync(
new Realm.Transaction() {
@Override
public void execute(Realm bgRealm) {
User user = bgRealm.createObject(User.class);
user.setName("John");
user.setEmail("john@corporation.com");
}
}, null);

20. Querying data
// Build the query looking at all users:
RealmQuery<User> query = realm.where(User.class);
// Add query conditions:
query.equalTo("name", "John");
query.or().equalTo("name", "Peter");
// Execute the query:
RealmResults<User> result1 = query.findAll();
// Or alternatively do the same all at once (the "Fluent interface"):
RealmResults<User> result2 = realm.where(User.class)
.equalTo("name", "John")
.or()
.equalTo("name", "Peter")
.findAll();

21. Query data supports
- Conditions like lessThan, greaterThan, contains, beginsWith etc
- Modifiers for ignoring Cases
- Logical Operations OR AND
- Sorting Ascending, Descending
- Chaining Queries
- Aggregations like SUM, MIN, MAX, AVG
- Synchronous, Asynchronous operations

22. Linked queries
public class Person extends RealmObject {
private String id;
private String name;
private RealmList<Dog> dogs;
// getters and setters
}
public class Dog extends RealmObject {
private String id;
private String name;
private String color;
// getters and setters
}

23. Linked queries
RealmResults<Person> r1 = realm.where(Person.class)
.equalTo("dogs.name", "Fluffy")
.findAll();
RealmResults<Person> r2 = r1.where()
.equalTo("dogs.color", "Brown")
.findAll();

24. Auto updating objects
Dog d1 = realm.where(Dog.class).equals("id", 123).findFirst();
// register a listener to get notified when the object is updated.
d1.registerChangeListener(new RealmChangeListener() {
@Override
public void onChange() {
// called once the query complete and on every update
// do something now that the obj is updated
}
});
// assume code below is in some other thread
// Retrieve the same dog as above
Dog d2 = realm.where(Dog.class).equals("id", 123).first();
realm.beginTransaction();
d2.setAge(12);
realm.commitTransaction();
// d1's change listener gets called after the commit.*

25. Migration
// Example migration adding a new class
RealmMigration MyMigration = new RealmMigration() {
@Override
public void migrate(DynamicRealm realm, long oldVersion, long newVersion) {
// DynamicRealm exposes an editable schema
RealmSchema schema = realm.getSchema();
if (oldVersion == 0) {
schema.create("Person")
.addField("id", long.class, FieldAttribute.PRIMARY_KEY)
.addField("name", String.class)
.addField("age", int.class);
oldVersion++;
}
}
}
// in your init
RealmConfiguration config = new RealmConfiguration.Builder(context).schemaVersion(1)
.migration(new MyMigration()) ;

26. More features
● Direct support for Json to Object store
● Notification for database change like CP
● Encryption support in built
● Adapters for binding data with views (Android)
● Cross Platform, same data can work across ios and android
● Robust 3rd parties addons

27. Limitations
● Managing memory is tricky
● Not Entirely NOSQL, need migration on schema Changes
● No support for auto incrementing primary keys
● Mutable, thread-confined objects.
● Slower write
● Increase method count and size of apk

28. Latest update
● Server side tech
○ Real time sync
○ Conflict resolution
○ Reactive event handling
○ Authentication
○ Access control
● Good to building offline experiences
● Not a managed service yet

29. Thank you!
Amrit Sanjeev
@amsanjeev
#blrdroid