painless persistence in a disconnected world
TRANSCRIPT
Why design for offline?
• A better USER EXPERIENCE!
• You always have something to show the user
• Reduce network requests and data transferred
• Saves battery
Designing for Offline
Offline architectureMVVM
MVP
MVC
VIPER
Flux
Clean Architecture
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They all have a modelMVVM
MVP
MVC
VIPER
Flux
Clean Architecture
ModelView
getData()
data
You’re doing it wrong!@Overrideprotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Setup initial views setContentView(R.layout.activity_main); // Load data and show it Retrofit retrofit = new Retrofit.Builder() .addConverterFactory(JacksonConverterFactory.create()) .baseUrl("http://api.nytimes.com/") .build(); service = retrofit.create(NYTimesService.class); service.topStories("home", "my-key").enqueue(new Callback<NYTimesResponse<List<NYTimesStory>>>() { @Override public void onResponse(Response<NYTimesResponse<List<NYTimesStory>>> response, Retrofit retrofit) { showList(response); } @Override public void onFailure(Throwable t) { showError(t); } }); }
You’re doing it right!@Overrideprotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Setup initial views setContentView(R.layout.activity_main); // Load data and show it Model model = ((MyApplication) getApplicationContext()).getModel(); model.getTopStories(new Observer() { @Override public void update(Observable observable, NYTimesResponse<List<NYTimesStory>> data) { showList(data); } }); }
Encapsulate data
ModelView
Cache
Database
Network
Repository pattern
ModelView
Cache
Database
Network
Repository
Business rules
Creating/fetching data
Repository pattern
• Repository only has CRUD methods:
• Create()
• Read()
• Update()
• Delete()
• Model and Repository can be tested separately.
Designing for offline
Repository… DatastoregetData()
Observable<Data>()
NetworkUpdate?
Save
Designing for offline• Encapsulate data access
• The datastore is single-source-of-truth
• Everything is asynchronous
• Observer pattern
• RxJava
• EventBus
• Testing becomes easier
Persisting data
File system
• Define hierarchy using folders
• No help from the framework
• Use cases: Images, JSON blobs
File system
// App internal filescontext.getFilesDir(); context.getCacheDir(); // App external filescontext.getExternalFilesDir(Environment.DIRECTORY_DOCUMENTS); context.getExternalCacheDir(); // SD CardEnvironment.getExternalStorageDirectory();
SharedPreferences
• Key-value store
• Simple XML file
• Use cases: Settings, Key/Value data
• Simple API’s and easy to use
SharedPreferences
// Save dataSharedPreferences pref = getPreferences(MODE_PRIVATE); SharedPreferences.Editor editor = pref.edit(); editor.putBoolean("key", true); editor.commit();
// Read data boolean data = pref.getBoolean("key", false);
Databases
• Use cases: Structured data sets
• Advanced composing and query capabilities
• Complex API’s
SQLite vs. the World
• SQLite (Relational)
• Realm (Object store)
• Firebase (Document oriented)
• Couchbase Lite (Document oriented)
• Parse (Document oriented)
The Relational Model
Relational data
Relational data
BCNF
Relational data
Relational data
m:n?
Relational data
Relational data
SELECT owner.name, dog.name, city.name FROM owner
INNER JOIN dog ON owner.dog_id = dog.id
INNER JOIN city ON owner.city_id = city.id
WHERE owner.name = 'Frank'
SQLite
String query = "SELECT " + Owner.NAME + ", " + Dog.NAME + ", " + City.NAME + " FROM " + Owner.TABLE_NAME
+ " INNER JOIN " + Dog.TABLE_NAME + " ON " + Owner.DOG_ID + " = " + Dog.ID
+ " INNER JOIN " + City.TABLE_NAME + " ON " + Owner.CITY_ID + " = " + City.ID
+ " WHERE " + Owner.NAME = "'" + escape(queryName) + "'";
SQLite
“Lets use an ORM”
Abstract the problem away
–Joel Spolsky
“All non-trivial abstractions, to some degree, are leaky.”
Solved problem?• ActiveRecord
• Androrm
• Blurb
• Cupboard
• DBFlow
• DBQuery
• DBTools
• EasyliteOrm
• GreenDAO
• Ollie
• Orman
• OrmLite
• Persistence
• RushORM
• Shillelagh
• Sprinkles
• SquiDB
• SugarORM
Realm?
Object Store
A
B C
D E F
G
VS
x
z
y
x y z
SELECT table1.x, table2.y, table3.z
FROM table1
INNER JOIN table2 ON table1.table2_id = table1.id
INNER JOIN table3 ON table1.table3_id = table3.id
References in SQL
A
B C
D E F
G
Realm.getA().getC().getF()
Object Store references
Zero-copy
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 } }
Realm ORM Realm SQLite
Benchmarks
http://static.realm.io/downloads/java/android-benchmark.zip
1.09%2.26%
3.79%4.55%
22.85%
13.37%
1% 1% 1% 1% 1% 1%
0%
5%
10%
15%
20%
25%
BatchWrite% SimpleWrite% SimpleQuery% FullScan% Sum% Count%
Speedu
p&vs.&SQLite&
Tests&/&1000&objects&
Realm%
SQLite%
SQLite vs. Realm• Part of Android
• Relational data model
• Based on SQL
• Public Domain
• One of the most tested pieces of software
• Need to map between SQL and Java objects (manually or ORM).
• Foreign collections is an unsolvable problem.
• Complex API’s
• Objects all the way down
• Zero copy architecture
• Cross-platform
• Supports encryption out of the box
• Open source*
• Custom query language
• Will add ~2500 methods + 800 kB of native code.
• Still in beta
“Talk is cheap. Show me the code.”
–Linus Torvalds
Adding Realm// ./build.gradlebuildscript { repositories { jcenter() } dependencies { classpath 'com.android.tools.build:gradle:2.0.0-alpha1' classpath 'io.realm:realm-gradle-plugin:0.86.0' } }
// ./app/build.gradleapply plugin: 'com.android.application'apply plugin: 'realm'
Models and Schemapublic class Person extends RealmObject { private String name; private int age; private Dog dog; private RealmList<Cat> cats;
// Autogenerated getters/setters}
public class Cat extends RealmObject { private String name;
// Autogenerated getters/setters}
public class Dog extends RealmObject { private String name;
// Autogenerated getters/setters}
Getting an Realm instance
// Default configuration. Schema is automatically detected RealmConfiguration config = new RealmConfiguration.Builder(context).build(); Realm.setDefaultConfiguration(config);
Realm realm = Realm.getDefaultInstance();
Create objects - Realm// Create and set persisted objectsrealm.beginTransaction(); Person person = realm.createObject(Person.class); person.setName("Young Person"); person.setAge(14); realm.commitTransaction();
// Copy java objectsPerson person = new Person(); person.setName("Young Person"); person.setAge(14); realm.beginTransaction(); realm.copyToRealm(person); realm.commitTransaction();
• Extend RealmObject
• POJO: Plain Old Java Object
Transactions - Realm
// Simple writesrealm.beginTransaction(); // ...realm.commitTransaction();
// Automatically handle begin/commit/cancelrealm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { // ... } });
QueriesRealmResults<Person> results = realm.where(Person.class) .equalTo("age", 99) .findAll();
RealmResults<Person> results = realm.where(Person.class) .equalTo("cats.name", “Tiger") .findAll();
RealmResults<Person> results = realm.where(Person.class) .beginsWith("name", “John") .findAllAsync();
results.addChangeListener(new RealmChangeListener() { @Override public void onChange() { showResults(results); } });
• Fluent queries
• Semi-typesafe
• Easy async
• Always up-to-date
Network data// Use Retrofit to parse objectsRetrofit retrofit = new Retrofit.Builder() .addConverterFactory(JacksonConverterFactory.create()) .baseUrl("http://api.nytimes.com/") .build(); MyRestApi service = retrofit.create(MyRestApi.class); final Data data = service.getData(); // Copy all data into Realmrealm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { realm.copyToRealmOrUpdate(data); } });
RxJava (Realm)
Observable<Realm> observableRealm = realm.asObservable();
Observable<RealmResults<Person>> results = realm.where(Person.class) .beginsWith("name", “John") .findAllAsync() .asObservable();
Observable<Person> results = realm.where(Person.class).findFirst().asObservable();
Observable<RealmQuery> results = realm.where(Person.class).asObservable();
Examplehttps://github.com/realm/realm-java/tree/cm/offline-
newsreader/examples/newsreaderExample
Take aways
• Not everyone is on Wifi or 4G networks
• Encapsulate data access
• Designing for offline gives a a better USER EXPERIENCE!
Resources• Repository Pattern: http://martinfowler.com/eaaCatalog/
repository.html
• Design for offline: https://plus.google.com/+AndroidDevelopers/posts/3C4GPowmWLb
• MVP example: https://www.code-labs.io/codelabs/android-testing/#0
• Optimizing network requests: https://www.youtube.com/playlist?list=PLWz5rJ2EKKc9CBxr3BVjPTPoDPLdPIFCE
• Realm : https://realm.io/docs/java/latest/
