Android course

Database

dr Milan VidakovićChair of Informatics

Faculty of Technical SciencesUniversity of Novi Sad

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Database

• What is relational database model?• simplified answer: database consists of tables

• table is just like the one in the Excel

• Each table has rows and columns• Each column has: name, type (int,

string,...), undefined value or not (null), is it primary key or not (primary key), etc.

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Primary key

• Primary key: a column(s) which identifies a row• Student index, vehicle registration plate

• Primary key can be autoincrement• Integer value which is incremented when a row is

inserted in a table

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Android database

• Android comes with SQLite database • Features:

• self-contained,

• serverless,

• zero-configuration and

• transactional

• All the tables are placed in the /data folder (the only read-write folder on Android (except for the /sdcard folder content – SD card))

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SQLite

• SQLiteDatabase class:

SQLiteDatabase db = dbHelper.getWritableDatabase();

SQLiteOpenHelper class: to open, close, create and modify database

DatabaseExamples

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Helper class

• Extends SQLiteOpenHelper class

• Overrides:• onCreate(SQLiteDatabase)• onOpen(SQLiteDatabase)• onUpgrade(SQLiteDatabase, old_ver, new_ver)• onDowngrade(SQLiteDatabase, old_ver,

new_ver)

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Helper classpublic class MyDbHelper extends SQLiteOpenHelper {

private static final String DATABASE_CREATE = "create table NOTES ( "

+ " _id integer primary key autoincrement, "

+ " naslov text not null, "

+ " vreme text not null, "

+ " tekst text not null);";

public MyDbHelper(Context context) {

super(context, DATABASE_NAME, null, DATABASE_VERSION);

}

@Override

public void onCreate(SQLiteDatabase _db) {

_db.execSQL(DATABASE_CREATE);

}

@Override

public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion) {

_db.execSQL("DROP TABLE IF EXISTS " + NotesDbManager.DATABASE_TABLE);

onCreate(_db);

}

}

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SQLite database

• CRUD (Create, Read, Update, Delete):long insert(String table, String null_hack, ContentCalues entry)

Cursor query (String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit)

int update(String table, ContentValues values, String whereClause, String[] whereArgs)

int delete(String table, String whereClause, String[] whereArgs)

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Insert

• Content to be inserted must be placed in the ContentValues map:

ContentValues newEntry = new ContentValues();

newEntry.put(“FirstName”, “Pera”);

newEntry.put(“LastName”, “Peric”);

long id = db.insert(DATABASE_TABLE, null, newEntry);

• Returns Id of the insterted row• Important when PK is autoincrement!

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Query

• Return value is a cursor which is used to browse query results

• If criteria, group by, having, order by, and limit is omitted, lists the whole table:

Cursor c = db.query(DATABASE_TABLE, new String[] { _ID, TITLE, TIMESTAMP, TEXT }, null, null, null, null, null);

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Query Query:

cursor = db.query(true, DATABASE_TABLE,

new String[] {_ID,TITLE,TIMESTAMP,TEXT},

_ID + "=?",

new String[] {id}, null, null, null, null);

• Raw query:

cursor = db.rawQuery("select _ID, TITLE, TIMESTAMP, TEXT from DATABASE_TABLE where ID=?", new String[] {id});

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Cursor• To browse and read query results

• Browse:move(offset)

moveToFirst(), moveToLast(), moveToNext(), moveToPrevious()

isFirst(), isLast(), isAfterLast(), isBeforeFirst()

• Read:getCount()

getString(column_index)

getInt(column_index)

getColumnIndex(“LastName”);

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Update• Updates column(s):ContentValues newValue = new ContentValues();newValue.put(“FirstName”, “MIKA”);newValue.put(“LastName”, “MIKIC”);int rows = db.update(DATABASE_TABLE, newValue,_ID + "=?", new String[] {id});

• SQL equivalent:

update DATABASE_TABLE set FirstName=“MIKA”, LastName=“MIKIC” where _ID=id

• If filter criteria is omitted, it will update all rows!

• Last two arguments are filter criteria and its parameters

• Returns the number of affected rows

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Delete

• Deletes a row:

int rows = db.delete(DATABASE_TABLE,

_ID + "=?", new String[] {id});

• SQL equivalent:

delete from DATABASE_TABLE where _ID=id If filter criteria is omitted, it will update all rows! Last two arguments are filter criteria and its parameters Returns the number of affected rows

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Data read

• To start reading query results:startManagingCursor(cur);

• This method binds cursor to Activity from which it has been created• If an activity is stopped, it will invoke cursor.deactivate()

• If an activity is restarted, it will invoke cursor.requery()

• If an activity is destroyed, it will close the cursor

• Each ListView has a ListAdapter which binds data and ListView

– SimpleCursorAdapter class is used to bind query results to a ListView

DatabaseExamples

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SimpleCursorAdapter

• A kind of ListAdapter, which binds cursor to a ListView

• Procedure: execute query, create SimpleCursorAdapter, and put that adapter as a soruce to a ListView

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SimpleCursorAdapter• Constructor:

ListAdapter adapter = new SimpleCursorAdapter(this,

R.layout.list_item,

cur,

new String[] { “FirstName”, “LastName”},

new int[] { R.id.firstname, R.id.lastname });

• Second argument (R.layout.list_item) is a resource ID which will visualise a row

• Third argument is a cursor

• Fourth argument is a list of column names in a db table

• Fifth argument is a list of component ids bound to appropriate columns in a table• Components are part of a row component (R.layout.list_item)

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List multimedia files

• List multimeida files on a device

String[] proj = { MediaStore.Video.Media._ID,

MediaStore.Video.Media.DATA,

MediaStore.Video.Media.DISPLAY_NAME,

MediaStore.Video.Media.SIZE };

mediaCursor = managedQuery(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, proj, null, null, null);

DatabaseExamples

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List multimedia files• How to bind query result and ListView?

Create custom Adapter, which extends BaseAdapterclass MMediaAdapter extends BaseAdapter {

private Context vContext;

public MMediaAdapter(Context c) {

vContext = c;

}

public int getCount() {

return mediaCursor.getCount();

}

public Object getItem(int position) {

return position;

}

public long getItemId(int position) {

return position;

}

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List multimedia filespublic View getView(int position, View oldView, ViewGroup parent) {

System.gc();

TextView tv;

String id = null;

if (oldView == null) {

tv = new TextView(vContext.getApplicationContext());

int media_column_index = mediaCursor

.getColumnIndexOrThrow(MediaStore.Video.Media.DISPLAY_NAME);

mediaCursor.moveToPosition(position);

id = mediaCursor.getString(media_column_index);

media_column_index = mediaCursor

.getColumnIndexOrThrow(MediaStore.Video.Media.SIZE);

mediaCursor.moveToPosition(position);

id += " Size(KB):" + mediaCursor.getString(media_column_index);

tv.setText(id);

} else

tv = (TextView) oldView;

return tv;

}

}

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Browse bookmarks and web history• Android browsers record all bookmarks and

history in a database

• Table has an alias: android.provider.Browser.BOOKMARKS_URI

• Columns:• Browser.BookmarkColumns.TITLE• Browser.BookmarkColumns.URL• Browser.BookmarkColumns.CREATED• Browser.BookmarkColumns.BOOKMARK – 1 for

a bookmark; 0 for historyDatabaseExamples

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Browse bookmarks and web historyString[] columns = new String[] { Browser.BookmarkColumns.TITLE,

Browser.BookmarkColumns.URL, Browser.BookmarkColumns.CREATED };

Cursor cur = managedQuery(android.provider.Browser.BOOKMARKS_URI,

columns, null, null, null);

ListAdapter adapter = new SimpleCursorAdapter(this, R.layout.bookmark_item,

cur,

new String[] { Browser.BookmarkColumns.TITLE,

Browser.BookmarkColumns.URL, Browser.BookmarkColumns.CREATED},

new int[] {

R.id.bookmark_title, R.id.bookmark_url, R.id.bookmark_created });

ListView mainList = (ListView) findViewById(R.id.bookmarks_list);

mainList.setAdapter(adapter);

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Call history

• Android records all voice calls history in a database

• Table alias: CallLog.Calls.CONTENT_URI

• Columns:• Calls.NUMBER

• Calls.CACHED_NAME

• Calls.DURATION

• Calls.DATE

• Calls.TYPE (incoming, outgoing, missed)

DatabaseExamples

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Call historyString[] columns = new String[] {Calls._ID , Calls.NUMBER,

Calls.CACHED_NAME, Calls.DURATION };

Cursor cur = managedQuery(CallLog.Calls.CONTENT_URI, columns, null,

null, null);

ListAdapter adapter = new SimpleCursorAdapter(this, R.layout.call_history_item,

cur,

new String[] { Calls.NUMBER,

Calls.CACHED_NAME, Calls.DURATION},

new int[] {

R.id.call_number, R.id.call_name, R.id.call_duration });

ListView mainList = (ListView)findViewById(R.id.call_history_list);

mainList.setAdapter(adapter);