Painless Persistence with Realm
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The document discusses the principles of designing applications for offline use, emphasizing the efficiency of using the Realm database as a NoSQL solution. It outlines the repository pattern for data management, improved user experience through reduced network requests, and a reactive UI that updates automatically with data changes. Key features include automatic synchronization between devices and a focus on asynchronous data handling for optimal performance.
Painless Persistence with Realm
- 1. Painless Persistence with Realm Foo Café Stockholm Christian Melchior @chrmelchior cm@realm.io
- 2. cm@realm.io
- 3. cm@realm.io
- 4. Design for offline • A better USER EXPERIENCE! • You always have something to show to the user. • Reduce network requests and data transferred. • Saves battery. • It is 2016. cm@realm.io
- 6. cm@realm.io They all have a model MVVM MVC Flux Clean Architecture MVP VIPER ModelView getData() data
- 7. cm@realm.io You’re doing it wrong @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Setup initial views setContentView(R.layout.activity_main); // Load data from the REST API and show it myApi = retrofit.create(NYTimesService.class); myApi.topStories("home", "my-key") .subscribe(new Action1<List<NYTimesStory>>() { @Override public void call(List<NYTimesStory> response) { showList(response); } }, new Action1<Throwable>() { @Override public void call(Throwable throwable) { showError(throwable); } }); }
- 8. cm@realm.io You’re doing it right @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Setup initial views setContentView(R.layout.activity_main); // Load data from the Model and show it model = ((MyApplication) getApplicationContext()).getModel(); model.getTopStories() .subscribe(new Action1<List<NYTimesStory>>() { @Override public void call(List<NYTimesStory> response) { showList(response); } }, new Action1<Throwable>() { @Override public void call(Throwable throwable) { showError(throwable); } }); }
- 11. Repository pattern • Repository only have CRUD methods. • Create() • Read() • Update() • Delete() • Model and repository can be tested separately. • http://hannesdorfmann.com/android/ evolution-of-the-repository-pattern cm@realm.io
- 12. cm@realm.io Designing for offline Repository… DatastoregetData() Observable<Data>() Network Update? Fetch Repository… DatastoregetData() Observable<Data>() Network Update? Save
- 13. Designing for offline • Encapsulate data access. • The datastore is “Single Source of Truth”. • Everything is asynchronous. • Observer pattern • RxJava • EventBus • Testing becomes easier. cm@realm.io
- 14. Realm cm@realm.io A Replacement for SQLite and ORM’s
- 15. Why choose Realm? cm@realm.io • A database designed for mobile from the ground up • NoSQL (but not schemaless) • Objects all the way down • Reactive • Cross-platform
- 17. What does Realm look like? cm@realm.io public class Person extends RealmObject { @PrimaryKey private long id; private String name; private int age; // References private Dog dog; private RealmList<Cat> cats; // Methods // … }
- 18. Saving data cm@realm.io realm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { // Create Object directly Person person = realm.createObject(Person.class); person.setId(1); person.setName("Young Person"); person.setAge(14); // Or insert a normal Java object Person p = new Person(1, "Young Person", 14); realm.insertOrUpdate(p); } });
- 19. Queries cm@realm.io // Synchronous queries RealmResults<Person> results = realm.where(Person.class) .between("age", 7, 9) .beginsWith("name", "Person") .isNull("dog") .findAll(); // Asynchronous queries RealmResults<Person> results = realm.where(Person.class) .equalTo("dogs.name", "Fido") .findAllAsync(); results.addChangeListener(new RealmChangeListener<RealmResults<Person>>() { @Override public void onChange(RealmResults<Person> results) { showUI(results); } });
- 20. Realm SQLite cm@realm.io A B C D E F G
- 21. cm@realm.io References are first class SELECT person.name, dog.name FROM person INNER JOIN dog ON person.dog_id = dog.id WHERE person.name = ‘Frank’ RealmResults<Person> results; results = realm.where(Person.class) .equalTo("name", "Frank") .findAll(); String name = results.first() .getDog().getName();
- 22. cm@realm.io References are first class • No JOIN’s. • No object-relational impedance mismatch. • ID’s not required for references. • Navigating the object graph is as fast as following normal references.
- 23. Zero copy / Lazy loading cm@realm.io Person { • name = Tommy • age = 8 • dog = { • name = Lassie } } Person { • name = Tommy • age = 8 • dog = { • name = Lassie } } Person { • name = Tommy • age = 8 • dog = { • name = Lassie } } PersonProxy { • name • age • dog } PersonProxy { • name • age • dog } Person { • name = Tommy • age = 8 • dog = { • name = Lassie } }
- 24. Zero copy / Lazy loading cm@realm.io • Realm is always Single Source of Truth • RealmResults ~= Typesafe Cursor • Memory efficient • No need for LIMIT and Load More buttons Caveat • Consider caching values if used in a loop.
- 25. cm@realm.io Threading model Model • MVCC • Each thread has a consistent view. • Thread confined objects. API’s • Change listeners Model • Your on your own API’s • Loaders • ContentObservers • ContentProviders • RxJava (3rd party) • SQLBrite (3rd party)
- 26. Implementing offline-first cm@realm.io In 3 easy steps
- 27. 3xR: Realm, Retrofit and RxJava cm@realm.io buildscript { dependencies { classpath 'io.realm:realm-gradle-plugin:2.0.2' } } dependencies { compile 'com.google.code.gson:gson:2.7' compile 'io.reactivex:rxjava:1.2.1' compile 'com.squareup.retrofit2:retrofit:2.1.0' compile 'com.squareup.retrofit2:converter-gson:2.1.0' compile 'com.squareup.retrofit2:adapter-rxjava:2.1.0' } apply plugin: 'realm-android'
- 28. 3xR-1: Setup Retrofit cm@realm.io public interface NYTimesService { @GET("svc/topstories/v1/{section}.json") Observable<List<NYTimesStory>> topStories( @Path("section") String section, @Query(value = "api-key", encoded = true) String apiKey); } Retrofit retrofit = new Retrofit.Builder() .addCallAdapterFactory(RxJavaCallAdapterFactory.create()) .addConverterFactory(GsonConverterFactory.create()) .baseUrl("http://api.nytimes.com/") .build(); NYTimesService api = retrofit.create(NYTimesService.class);
- 29. 3xR-2: Save data cm@realm.io // Load data from the network and insert into Realm api.topStories("home", apiKey).asObservable().subscribe(new Action1<List<NYTimesStory>>() { @Override public void call(final List<NYTimesStory> stories) { Realm realm = Realm.getDefaultInstance(); realm.executeTransaction(r -> { r.insertOrUpdate(stories); }); realm.close(); } }, new Action1<Throwable>() { @Override public void call(Throwable throwable) { retryOrHandleError(throwable); } });
- 30. 3xR-3: Listen for changes cm@realm.io // Realm Observables never complete, updating your UI if anything changes Realm realm = Realm.getDefaultInstance(); realm.where(NYTimesStory.class) .findAllSortedAsync("published_date", Sort.DESCENDING) .asObservable() .subscribe(new Action1<RealmResults<NYTimesStory>>() { @Override public void call(RealmResults<NYTimesStory> stories) { updateUI(stories); } });
- 31. 3xR: Benefits cm@realm.io • Offline first with very few lines of code. • Decouple Network and UI . • Reactive UI: No matter where the update come from, your UI will reflect it.
- 32. Realm Mobile Platform cm@realm.io Automatic synchronisation between devices
- 34. Synchronising changes • Server always wins • Easy • Client not allowed to write or risk loosing changes. • Client can win • Hard • Complexity explosion • Changes needs to be tracked and merged. cm@realm.io
- 35. What if we removed all that? cm@realm.io Native Realm Object Realm Object Server Only Realm Native object JSON Backend object SQL Backend object JSON Native object SQLite/CoreData SQLite/CoreData e.g. Firebase, Parse, etc.
- 36. Synchronising a local Realm cm@realm.io apply plugin: 'realm-android' realm { syncEnabled = true }
- 37. cm@realm.io SyncCredentials creds = SyncCredentials.usernamePassword(username, password, createUser); SyncUser.loginAsync(creds, "https://my.server/auth", new SyncUser.Callback() { @Override public void onSuccess(SyncUser user) { openRealm(user); } @Override public void onError(ObjectServerError error) { handleError(error); } }); Synchronising a local Realm
- 38. cm@realm.io // Opening a local Realm RealmConfiguration config = new RealmConfiguration.Builder().build(); Realm realm = Realm.getInstance(config); // Opening a synchronized Realm SyncUser user = login(); String url = "realm://my.server/~/default"; SyncConfiguration config = new SyncConfiguration.Builder(user, url).build(); Realm realm = Realm.getInstance(config); Synchronising a local Realm
- 39. Features cm@realm.io • Automatic conflict resolution using Operational Transform. • Offline first. • Same reactive pattern on the Client and the Server. • Node.js API on the server side for integration with other DB’s or API’s.
- 40. Take aways cm@realm.io • Design for offline first - no excuse in 2016 • Repository pattern for decoupling and testability. • Try Realm - https://realm.io/