Object-Oriented Databases Object-Relational Mappings and Frameworks. Alexandre de Spindler Department of Computer Science

Transcription

1 Object-Oriented Databases Object-Relational Mappings and Frameworks

2 Challenges Development of software that runs on smart phones. Data needs to outlive program execution Use of sensors Integration with other applications on mobile device

3 Google Android Linux-based operating system Default applications Search, Maps, Mail, Calendar, Chat, Contacts etc. Java API supporting the development of applications Support for persistent data management, use of sensors and integration with other applications Application component model

4 APPLICATION COMPONENT MODEL

5 Example Application: Contact Management Computation UI Data Model

6 Example Application: Picture Tagging UI Computation Data Model

7 Application Component Model Activity (UI) Service (API, Computation) Broadcast Receiver (Events) Content Provider (Data Management) A Manifest lists the application components as well as the activity to be shown on start up. Furthermore, components may be made available to other applications. An Intent is used to request the use of application components. e.g. showing activities, using content providers, listening to events or starting services

8 Intents Activities, content providers, services and events are activated by means of intents. Using intents, application components may be activated during application run time. Intents contain a specification of an operation to be executed or an event of interest. e.g. showing an activity, starting a service, sensor updates

9 Application Lifecycle An application has a class implementing the activity interface. This interface declares the methods that will be invoked upon state changes. Thus, the application may react to such changes.

10 DATA MANAGEMENT Lower level: SQL-based Higher level: Content Provider

11 Database Instance SQLiteDatabase db = context.openorcreatedatabase( "Persons", Context.MODE_PRIVATE, null); db.execsql( "create table persons ( person_id integer primary key autoincrement, name text, phone text );"); db.rawquery( SELETC * FROM Persons"); Cursor cursor = db.rawquery( SELECT * FROM Persons"); while (!cursor.islast()) { System.out.println(cursor.getString(0)); cursor.movetonext(); }

12 Datenbank-Instanz (Android) StringDBOpenHelper dbhelper = new StringDBOpenHelper(); SQLiteDatabase db = dbhelper.getwritabledatabase(); Cursor cursor = db.rawquery( SELECT * FROM strings"); while (!cursor.islast()) { System.out.println(cursor.getString()); cursor.movetonext(); } public class StringDBOpenHelper extends SQLiteOpenHelper { StringDBOpenHelper(Context context) { super(context, "StringDB", null, 1); } public void oncreate(sqlitedatabase db) { db.execsql("create TABLE strings (value TEXT);"); }

13 SQLiteDatabase CRUD Create (Insert) ContentValues values = new ContentValues(); values.put( name, Damian Marley ); values.put( height, 185); db.insert( Persons, null, values); Read (Retrieve, Query) Update Delete Cursor result = db.query( Persons, new String[]{ name, height }, name like? AND height > 180, new String[]{ marley }, null, null, null); ContentValues newvalues = new ContentValues(); newvalues.put( name, Damien Marley ); db.update ( Persons, newvalues, name =?, new String[]{ Damian Marley });

14 ContentValue A ContentValue object is a map containing base typed values only. Similar to a map, values can be put and get by means of a key. In the case of providing a ContentValue object to an insert method, the keys are used as the names of the relational attributes.

15 Cursor A Cursor object is an iterator over a result set. Using the methods islast() and movetonext(), the result set (set of tuples) can be traversed. Within a tuple, values are accessed by means of type-specific getter methods. e.g. getint(3) retrieves the value of the third column and returns it as of type int. There are methods for the common base types. The method getcolumnindex(string). is used to retrieve a column index using its name.

16 Content Provider The ContentProvider allows all data management aspects to be encapsulated within the application as well as to be shared with other applications. For example, a content provider encapsulates a relational database and provides an object-oriented interface supporting CRUD operations. Typically, content providers are not used by an application directly. Instead, a request for operation is handed over to a ContentResolver, which forwards it to the content provider selected (cf. Intent).

17 Content Provider ContentProvider is an abstract class implemented by an application. The following methods are declared by the ContentProvider class. oncreate() query(uri, String[], String, String[], String) insert(uri, ContentValues) update(uri, ContentValues, String, String[]) delete(uri, String, String[]) gettype(uri) All of these methods make use of the concepts Cursor, ContentValue and URI.

18 URIs Within a content provider, URIs are defined that identify data managed by the provider. content://ch.zhaw.zwi.me.personprovider content://ch.zhaw.zwi.me.personprovider/employers content://ch.zhaw.zwi.me.personprovider/pictures In the manifest, the content provider is registered along with the URIs specified. URIs do not necessarily need to correspond directly to the database schema.

19 Anatomy of an URI content://ch.acm.personprovider/pictures/12 content:// says that this URI identifies data managed by a content provider. ch.acm.personprovider identifies a content provider. pictures identifies a subset of the data managed by the content provider (as defined by the provider). 12 identifies a tuple by means of an id. Content providers split a URI received and interpret/execute the operation to be executed.

20 Example Application /employees /MyCompany/employees

21 Content Resolver Ein Content Resolver erlaubt es, gegeben einer URI, CRUD-Operationen auf dem mit der gegebenen URI identifizierten Content Provider auszuführen. Der Content Resolver selektioniert einen Content Provider mittels dem Manifest. Der Content Resolver stellt die CRUD-Operationen selber zur Verfügung, leitet diese aber an den selektionierten Content Provider weiter.

22 USE OF SENSORS

23 Location API

24 Location API Location Provider, e.g. GPS Provider Network Provider (Cell Tower ID, Wi-Fi) Location Listener Receives updates from location sensor Location Manager Choose location provider Get last known location Location lastknownlocation = locationmanager.getlastknownlocation(locationprovider); Register location listener (how often, after how much change)

25 Location API LocationManager locationmanager = (LocationManager) this.getsystemservice(context.location_service); LocationListener locationlistener = new LocationListener() { public void onlocationchanged(location location) { // Called when a new location is found } public void onstatuschanged(string provider, int status, Bundle extras) {} public void onproviderenabled(string provider) {} public void onproviderdisabled(string provider) {} }; locationmanager.requestlocationupdates(locationmanager.network_provider, 0, 0, locationlistener); <manifest... > <uses-permission android:name="android.permission.access_fine_location" />... </manifest>

26 Bluetooth API: Information Sharing BluetoothAdapter mbluetoothadapter = BluetoothAdapter.getDefaultAdapter(); BluetoothServerSocket serversocket = mbluetoothadapter.listenusingrfcommwithservicerecord(string, UUID); BluetoothSockeet socket = serversocket.accept(); BluetoothSocket socket = device.createrfcommsockettoservicerecord(my_uuid); socket.connect(); BluetoothSockeet socket = serversocket.accept(); in = socket.getinputstream(); byte[1024] buffer; in.read(buffer); in.close(); socket.close(); byte[] bytes; socket.write(bytes); socket.close();

27 Bluetooth API: Proximity Sensing private final BroadcastReceiver mreceiver = new BroadcastReceiver() { public void onreceive(context context, Intent intent) { String action = intent.getaction(); // When discovery finds a device if (BluetoothDevice.ACTION_FOUND.equals(action)) { // Get the BluetoothDevice object from the Intent BluetoothDevice device = intent.getparcelableextra( BluetoothDevice.EXTRA_DEVICE); // access name device.getname() // access address device.getaddress()); } } }; IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND); registerreceiver(mreceiver, filter);