SQLite Database

SQLite Public domain database – Advantages Small (about 150 KB) – Used on devices with limited resources Each database contained within one file – Can be seen in file explorer /data/data/packagename/database/ Self-contained – no special administration needed

SQLite Primary components – SQLiteOpenHelper android.database.sqlite.SQLiteOpenHelper manages aspects of the database – creating or opening database – SQLiteDatabase android.database.sqlite.SQLiteDatabase – methods to interface with database via SQL – Cursor android.database.Cursor – provides access to result set returned by a query

Typical Approaches Approach 1: Providing a database with the app – store.db file in Assets folder.db file created within Android.db file created in other SQLite manager, such as Firefox plug-in – in onCreate() of extended Activity, copy the database if it does not already exist in the device’s internal memory – onCreate() method in extended SQLiteOpenHelper class typically empty Approach 2: Database created when app first run – onCreate() method in extended SQLiteOpenHelper class contains SQL to create database – will only run if the database does not exist

SQLiteOpenHelper class

SQLiteOpenHelper Abstract class – Subclass in a new.java file – Useful methods onCreate (abstract) – called when DB first created – table creation done here onUpgrade (abstract) – called when DB is changed (i.e. during new app release) – essentially used to drop and recreate database getReadableDatabase – called to get a read-only version of database getWriteableDatabase – called to get an editable version of database

Sample code - SQLiteOpenHelper public class MyClass extends SQLiteOpenHelper { public MyClass (Context ctx) { //Parameters: Context, file name, CursorFactory factory, database version) //CursorFactory rarely used – only used for customized Cursors super (ctx, "myfilename.db", null, 1); } public void onUpgrade (SQLiteDatabase db, int oldVer, int newVer) { db.execSQL("DROP TABLE IF EXISTS TABLE_NAME"); onCreate(db); } public void onCreate(SQLiteDatabase db) { //_id field must be included!!! db.execSQL("CREATE TABLE MYTABLE (_id INTEGER PRIMARY KEY AUTOINCREMENT,..."); }

SQLiteDatabase class

SQLiteDatabase Concrete class – SQL methods Convenience methods – query – returns a Cursor – insert – returns _id of new record or –1 if error occurred – update – returns number of rows affected – delete – number of rows affected (0 if no where clause) » pass ‘1’ as where clause to get count in this case Manual creation of SQL – rawQuery » can execute any SELECT statement and returns a Cursor – execSQL » can execute any SQL statement that is not a SELECT void return type

SQLiteDatabase query method – Parameters String – table name String [] – columns to select – _id field must be included if displaying in List String – where clause (without the word WHERE) – null if not wanted – ? for arguments String [] – selection clause, to allow arguments for field names in where clause – only if ? in preceding string String – group by clause (without the words GROUP BY) String – having clause (without the word HAVING) String – order by clause (without the words ORDER BY)

Sample code – query String [] FROM = {List of desired columns to select}; SQLiteDatabase db = myInstanceOfSQLiteOpenHelper.getReadableDatabase(); Cursor myCursor = db.query(MY_TABLE_NAME, FROM, null, null, null, null, null);

SQLiteDatabase insert method – Parameters String – table name String – work around to allow insertion of empty row in SQL – nullColumnHack – SQLLite does not allow: » INSERT INTO MYTABLE – ContentValues will be null ContentValues – Object holding the corresponding field names and values

Sample code – insert SQLiteDatabase db = myInstanceOfSQLiteOpenHelper.getWritableDatabase(); ContentValues values = new ContentValues(); values.put(COLUMN_NAME, column value);... values.put(COLUMN_NAME, column value); db.insert(MY_TABLE_NAME, null, values);

SQLiteDatabase update method – Parameters String – table name ContentValues – Object holding the corresponding field names and values String – where clause (without the word WHERE) String [] – selection clause, to allow arguments for field names in where clause

Sample code – update SQLiteDatabase db = myInstanceOfSQLiteOpenHelper.getWritableDatabase(); String where = "My WHERE clause (without the word WHERE)"; ContentValues values = new ContentValues(); values.put(COLUMN_NAME, column value);... values.put(COLUMN_NAME, column value); db.update(MY_TABLE_NAME, values, where, null);

SQLiteDatabase delete method – Parameters String – table name String – where clause (without the word WHERE) String [] – selection clause, to allow arguments for field names in where clause

Sample code – delete SQLiteDatabase db = myInstanceOfSQLiteOpenHelper.getWritableDatabase(); String where = "My WHERE clause (without the word WHERE)"; db.delete(MY_TABLE_NAME, where, null);

SQLiteDatabase rawQuery method – Parameters String – SQL statement String [] – selection clause, to allow arguments for field names in where clause

Sample code – rawQuery SQLiteDatabase db = myInstanceOfSQLiteOpenHelper.getWritableDatabase(); Cursor myCursor = db.rawQuery(“ SQL statement here”, null);

SQLiteDatabase execSQL method – Parameters String – SQL statement

Sample code – execSQL SQLiteDatabase db = myInstanceOfSQLiteOpenHelper.getWritableDatabase(); db.execSQL(“SQL statement here”);

Cursor class

Aspects of Cursor class SQLiteDatabase query method returns a Cursor – Cursor must be managed by Activity Cursor class allows manipulation of pointer – move, moveToFirst, moveToNext, moveToPosition, etc. Cursor class allows retrieval of data – getInt, getDouble, getString, etc. – must provide column position Cursor can be associated with an Adapter – typically SimpleCursorAdapter

Sample code – Cursor data retrieval Retrieving the integer in the 4 th row, 3 rd column myCursor.moveToPosition(3); int x = myCursor.getInt(2);

Sample code – populating a Cursor from a Database private Cursor populateCursor() { String [] FROM = {List of desired DB field names}; SQLiteDatabase db = myInstanceOfSQLiteHelper.getReadableDatabase(); Cursor myCursor = db.query(MY_TABLE_NAME, FROM, null, null, null, null, null); return myCursor; }

Sample code – displaying Cursor contents in a ListView private void displayRecords(Cursor c) { String [] from = {List of desired field names to display}; int [] to = new int [] {List of TextViews to display field names (i.e. R.id.myTextView)}; ListView lv = (ListView)findViewById(R.id.myListView); SimpleCursorAdapter records = new SimpleCursorAdapter(this, R.layout.my_file_for_TextViews, c, from, to); lv.setAdapter(records); }