Android Data Persistence

Android: data persistence Romain Rochegude 2016.09.30 1

Introduction • POO basics: modeling the domain • Modeling domain objects and their interactions • Data bound with a remote API • Need of a local database 3

The “raw” way private static final String SQL_CREATE_ENTRIES = "CREATE TABLE REPO (" + "_ID INTEGER PRIMARY KEY," + "NAME TEXT)"; private static final String SQL_DELETE_ENTRIES = "DROP TABLE IF EXISTS REPO "; 5

• Subclass SQLiteOpenHelper public class ReposDbHelper extends SQLiteOpenHelper { public static final int DATABASE_VERSION = 1; public static final String DATABASE_NAME = "repos.db"; public ReposDbHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } 6

//... public void onCreate(SQLiteDatabase db) { db.execSQL(SQL_CREATE_ENTRIES); } public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { db.execSQL(SQL_DELETE_ENTRIES); onCreate(db); } } 7

• Get an instance of SQLiteOpenHelper ReposDbHelper dbHelper = new ReposDbHelper(getContext()); 8

• Put Information into a Database SQLiteDatabase db = dbHelper.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("name", "a sample name"); long newRowId = db.insert("REPO", null, values); 9

• Read Information from a Database SQLiteDatabase db = dbHelper.getReadableDatabase(); String[] projection = { "_id", "name" }; String selection = "NAME = ?"; String[] selectionArgs = { "a sample name" }; String sortOrder = "NAME DESC"; 10

Cursor cursor = db.query( "REPO", projection, selection, selectionArgs, null, null, sortOrder); cursor.moveToFirst(); long itemId = cursor.getLong( cursor.getColumnIndexOrThrow("_ID") ); 11

The ContentProvider way • Provide a ContentProvider subclass dedicated to the application public class RepoProvider extends ContentProvider { } 12

• Define a specific UriMatcher and configure available URI public class RepoProvider extends ContentProvider { private static final UriMatcher sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH); } 13

static { sUriMatcher.addURI("fr.test.app.provider", "repo", 1); sUriMatcher.addURI("fr.test.app.provider", "repo/#", 2); } 14

• Override various CRUD methods public Cursor query( Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { //... 15

//... switch (sUriMatcher.match(uri)) { case 2: selection = selection + "_ID = " + uri.getLastPathSegment(); break; default: //... } 16

• Use it through a ContentResolver instance mCursor = getContentResolver().query( "fr.test.app.provider/repo/2", mProjection, mSelectionClause, mSelectionArgs, mSortOrder); 17

• Refer to the open-sourced Google’s iosched application • Helpful libraries to simplify the deal with a ContentProvider: • ProviGen • AutoValue: Cursor Extension 18

Async management • Perform CRUD operations outside of the main thread 19

Query data using Loader • To query the ContentProvider in an Activity, make it implementing LoaderManager.LoaderCallbacks<Cursor> public class ReposListActivity extends FragmentActivity implements LoaderManager.LoaderCallbacks<Cursor> { } 20

• Start loading data with a loader identiﬁer getLoaderManager() .initLoader(LOADER_REPOS, null, this); • Implement LoaderCallbacks. . . 21

• . . . to create the CursorLoader @Override public Loader<Cursor> onCreateLoader( int id, Bundle bundle) { if(id == LOADER_REPOS) { return new CursorLoader( this, "fr.test.app.provider/repo", mProjection, null, null, null); } //... } 22

• . . . and deal with result @Override public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) { if(loader.getId() == LOADER_REPOS){ // ... } } 23

• See also: AsyncQueryHandler 24

The well-known: ORMLite • Declare your model using ORMLite annotations @DatabaseTable(tableName = "REPO") public class RepoEntity { @DatabaseField(columnName = "_ID", generatedId = true) public long _id; @DatabaseField public String name; } 26

• declare the corresponding DAO public class DAORepo extends BaseDaoImpl<RepoEntity, Long> { public DAORepo(ConnectionSource cs) throws SQLException { this(cs, RepoEntity.class); } //... } 27

• subclass OrmLiteSqliteOpenHelper public class DatabaseHelperTest extends OrmLiteSqliteOpenHelper { private static final String DATABASE_NAME = "test.db"; private static final int DATABASE_VERSION = 1; //... 28

//... public DatabaseHelperTest( Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION, R.raw.ormlite_config); } //... 29

//... @Override public void onCreate(SQLiteDatabase db, ConnectionSource cs) { TableUtils.createTable(cs, RepoEntity.class); } @Override public void onUpgrade(SQLiteDatabase db, ConnectionSource cs, int oldVersion, int newVersion) { //... } 30

• get the requested DAO DatabaseHelperTest helper = //... ConnectionSource cs = helper.getConnectionSource(); DatabaseTableConfig<RepoEntity> tableConfig = DatabaseTableConfigUtil.fromClass(cs, RepoEntity.class); DAORepo dao = new DAORepo(cs, tableConfig); 31

• perform CRUD operations // create RepoEntity repo = new RepoEntity("a sample name"); dao.create(repo); 32

// read List<RepoEntity> repos = dao.queryBuilder() .where() .eq("name", "a sample name") .query(); 33

• Performance: orm-gap gradle plugin buildscript { repositories { mavenCentral() } dependencies { classpath 'com.github.stephanenicolas.ormgap' + ':ormgap-plugin:1.0.0-SNAPSHOT' } } apply plugin: 'ormgap' 34

• generate an ORMLite configuration file that boosts DAOs creations • to use this file public RepoDatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION, R.raw.ormlite_config); } 35

The attractive way: requery • Object mapping • SQL generator • RxJava and Java 8 support • No reﬂection, compile-time processing and generation • Relationships support • Callback method (@PostLoad) • Custom type converters 36

• Deﬁne object mapping @Entity abstract class Repo { @Key @Generated int id; String name; } 37

• Easy to perform SQL queries Result<Repo> repos = data .select(Repo.class) .where(Repo.NAME.lower().like("%sample%")) .orderBy(Repo.ID.desc()) .get(); 38

Async management: RxJava • Get a speciﬁc instance of SingleEntityStore DatabaseSource dbSource = new DatabaseSource(context, Models.DEFAULT, "test.db", 1); Configuration conf = dbSource.getConfiguration(); SingleEntityStore<Persistable> data = RxSupport.toReactiveStore(new EntityDataStore<>(conf)); 39

• and use it the RX way data.select(RepoEntity.class) .get() .subscribeOn(Schedulers.newThread()) .subscribe(/*...*/) 40

Conclusion • Personal assessments of each way ContentProvider ORMLite requery setup - + + performance + - + readability - + + maintainability - + + 42

Android Data Persistence

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