Unit 4: SQLite database connectivity

javapublic class DBHelper extends SQLiteOpenHelper {
    static final String DB = "college.db";
    static final int VERSION = 1;
    public DBHelper(Context c) { super(c, DB, null, VERSION); }

    @Override public void onCreate(SQLiteDatabase db) {          // first use
        db.execSQL("CREATE TABLE student (_id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                   "name TEXT NOT NULL, course TEXT, marks INTEGER)");
    }
    @Override public void onUpgrade(SQLiteDatabase db, int oldV, int newV) {   // version change
        db.execSQL("DROP TABLE IF EXISTS student");
        onCreate(db);
    }
}

• onCreate runs once when the database file is first created; onUpgrade runs when VERSION increases — migrate data rather than dropping tables in real apps.

• getWritableDatabase() opens for reading and writing (creating or upgrading if needed); getReadableDatabase() opens for reading (falls back to read-only if the disk is full); close() releases the connection, usually when the helper is no longer needed.

javaSQLiteDatabase db = new DBHelper(this).getWritableDatabase();
ContentValues cv = new ContentValues();             // key–value set of column values
cv.put("name", "Aman");
cv.put("course", "B.Sc IT");
cv.put("marks", 82);
long id = db.insert("student", null, cv);           // returns row id, or −1 on error

javaContentValues upd = new ContentValues();
upd.put("marks", 88);
int rows = db.update("student", upd, "_id = ?", new String[]{String.valueOf(id)});

int deleted = db.delete("student", "marks < ?", new String[]{"40"});

javaCursor c = db.query("student", new String[]{"_id", "name", "marks"},
        "course = ?", new String[]{"B.Sc IT"}, null, null, "marks DESC");
// or: db.rawQuery("SELECT name, marks FROM student WHERE marks >= ?", new String[]{"60"});
while (c.moveToNext()) {
    String name = c.getString(c.getColumnIndexOrThrow("name"));
    int marks = c.getInt(c.getColumnIndexOrThrow("marks"));
}
c.close();

• SQLite uses dynamic typing with type affinity: a column's declared type suggests, but does not force, the storage class.

• Content provider: a component that offers an app's data to other apps through a standard interface, addressed by a content URI — content://authority/path/id.

javaCursor c = getContentResolver().query(
        ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
        new String[]{ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME,
                     ContactsContract.CommonDataKinds.Phone.NUMBER},
        null, null, ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME + " ASC");

• Creating a provider: extend ContentProvider and implement onCreate, query, insert, update, delete and getType; declare it in the manifest with an authority; use a UriMatcher to map URIs to tables.
• Built-in providers: Contacts, Calendar, MediaStore (images, audio, video), Settings, call log.