Multiple Table SQLite DB Adapter(s) in Android?

Question

I was reading the Android SQLite NotePad tutorial that referenced creating a DB Adapter class to create and access a DB table. When dealing with a multi-table SQLite Databa

Answer 1

Here is the solution I eventually ended up implementing. It's kind of a mash-up from info gained in the Commonsware books, and some stuff around the web that I wish I bookmarked cause I want to give credit:

For each type of data that I need to pull from the db, I create an "adapter" class (not subclassed from anything). These adapter classes hold all of the methods necessary for accessing the db for that piece of info. For example, if I had three tables in my db:

1. Cars
2. Boats
3. Motorcycles

I would have three adapters that would look similar to the following(I'm only putting in one as a demo, but the idea is the same for each):

public class CarsDBAdapter {
    public static final String ROW_ID = "_id";
    public static final String NAME = "name";
    public static final String MODEL = "model";
    public static final String YEAR = "year";

    private static final String DATABASE_TABLE = "cars";

    private DatabaseHelper mDbHelper;
    private SQLiteDatabase mDb;

    private final Context mCtx;

    private static class DatabaseHelper extends SQLiteOpenHelper {

        DatabaseHelper(Context context) {
            super(context, DBAdapter.DATABASE_NAME, null, DBAdapter.DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        }
    }

    /**
     * Constructor - takes the context to allow the database to be
     * opened/created
     * 
     * @param ctx
     *            the Context within which to work
     */
    public CarsDBAdapter(Context ctx) {
        this.mCtx = ctx;
    }

    /**
     * Open the cars database. If it cannot be opened, try to create a new
     * instance of the database. If it cannot be created, throw an exception to
     * signal the failure
     * 
     * @return this (self reference, allowing this to be chained in an
     *         initialization call)
     * @throws SQLException
     *             if the database could be neither opened or created
     */
    public CarsDBAdapter open() throws SQLException {
        this.mDbHelper = new DatabaseHelper(this.mCtx);
        this.mDb = this.mDbHelper.getWritableDatabase();
        return this;
    }

    /**
     * close return type: void
     */
    public void close() {
        this.mDbHelper.close();
    }

    /**
     * Create a new car. If the car is successfully created return the new
     * rowId for that car, otherwise return a -1 to indicate failure.
     * 
     * @param name
     * @param model
     * @param year
     * @return rowId or -1 if failed
     */
    public long createCar(String name, String model, String year){
        ContentValues initialValues = new ContentValues();
        initialValues.put(NAME, name);
        initialValues.put(MODEL, model);
        initialValues.put(YEAR, year);
        return this.mDb.insert(DATABASE_TABLE, null, initialValues);
    }

    /**
     * Delete the car with the given rowId
     * 
     * @param rowId
     * @return true if deleted, false otherwise
     */
    public boolean deleteCar(long rowId) {

        return this.mDb.delete(DATABASE_TABLE, ROW_ID + "=" + rowId, null) > 0; //$NON-NLS-1$
    }

    /**
     * Return a Cursor over the list of all cars in the database
     * 
     * @return Cursor over all cars
     */
    public Cursor getAllCars() {

        return this.mDb.query(DATABASE_TABLE, new String[] { ROW_ID,
                NAME, MODEL, YEAR }, null, null, null, null, null);
    }

    /**
     * Return a Cursor positioned at the car that matches the given rowId
     * @param rowId
     * @return Cursor positioned to matching car, if found
     * @throws SQLException if car could not be found/retrieved
     */
    public Cursor getCar(long rowId) throws SQLException {

        Cursor mCursor =

        this.mDb.query(true, DATABASE_TABLE, new String[] { ROW_ID, NAME,
                MODEL, YEAR}, ROW_ID + "=" + rowId, null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    /**
     * Update the car.
     * 
     * @param rowId
     * @param name
     * @param model
     * @param year
     * @return true if the note was successfully updated, false otherwise
     */
    public boolean updateCar(long rowId, String name, String model,
            String year){
        ContentValues args = new ContentValues();
        args.put(NAME, name);
        args.put(MODEL, model);
        args.put(YEAR, year);

        return this.mDb.update(DATABASE_TABLE, args, ROW_ID + "=" + rowId, null) >0; 
    }

}

So if you imagine I have one of these classes "adapters" for each table.

When my app splash screen starts, I use the technique presented Android For Beginners: Creating multiple SQLite Tables for Android

So my main DBAdapter (which is responsible for creating all of my tables in a single db) looks like this:

public class DBAdapter {

    public static final String DATABASE_NAME = "stuffIOwn"; //$NON-NLS-1$

    public static final int DATABASE_VERSION = 1;

    private static final String CREATE_TABLE_CARS =
       "create table cars (_id integer primary key autoincrement, " //$NON-NLS-1$
    + CarsDBAdapter.NAME+ " TEXT," //$NON-NLS-1$
    + CarsDBAdapter.MODEL+ " TEXT," //$NON-NLS-1$
    + CarsDBAdapter.YEAR+ " TEXT" + ");"; //$NON-NLS-1$ //$NON-NLS-2$

    private static final String CREATE_TABLE_BOATS = "create table boats (_id integer primary key autoincrement, " //$NON-NLS-1$
    +BoatsDBAdapter.NAME+" TEXT," //$NON-NLS-1$
    +BoatsDBAdapter.MODEL+" TEXT," //$NON-NLS-1$
    +BoatsDBAdapter.YEAR+" TEXT"+ ");"; //$NON-NLS-1$  //$NON-NLS-2$

        private static final String CREATE_TABLE_CYCLES = "create table cycles (_id integer primary key autoincrement, " //$NON-NLS-1$
    +CyclesDBAdapter.NAME+" TEXT," //$NON-NLS-1$
    +CyclesDBAdapter.MODEL+" TEXT," //$NON-NLS-1$
    +CyclesDBAdapter.YEAR+" TEXT"+ ");"; //$NON-NLS-1$  //$NON-NLS-2$


    private final Context context; 
    private DatabaseHelper DBHelper;
    private SQLiteDatabase db;

    /**
     * Constructor
     * @param ctx
     */
    public DBAdapter(Context ctx)
    {
        this.context = ctx;
        this.DBHelper = new DatabaseHelper(this.context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper 
    {
        DatabaseHelper(Context context) 
        {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) 
        {
            db.execSQL(CREATE_TABLE_CARS);
            db.execSQL(CREATE_TABLE_BOATS);
            db.execSQL(CREATE_TABLE_CYCLES);           
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, 
        int newVersion) 
        {               
            // Adding any table mods to this guy here
        }
    } 

   /**
     * open the db
     * @return this
     * @throws SQLException
     * return type: DBAdapter
     */
    public DBAdapter open() throws SQLException 
    {
        this.db = this.DBHelper.getWritableDatabase();
        return this;
    }

    /**
     * close the db 
     * return type: void
     */
    public void close() 
    {
        this.DBHelper.close();
    }
}

The DBAdapter class only gets called when the app first starts and its only responsibility is to create/upgrade the tables. All other access to the data is done through the individual "adapter" class. I've found that this works perfectly and does not create the versioning issues that I mentioned earlier.

Hope this helps.

Answer 2

Had the same problem, tried many solutions, finnaly i made an abstract method wich constructs the database structure and has extended class for the table classes.

This is my Database constructor class and is Abstract:

public abstract class dbAdapter {
    public static String DATABASE_NAME = "";
    public static final int DATABASE_VERSION = 1;
    public static final String DATABASE_TABLE1 = "ContactName";
    public static final String DATABASE_TABLE2 = "PhoneNumber";

    public static DbHelper ourHelper;
    public static Context ourContext;
    public static SQLiteDatabase ourDatabase;

    boolean ourConstructorBool = false;
    boolean ourDB = false;

    public static final String ContactNameTable = "CREATE TABLE "+DATABASE_TABLE1+" (" +
        ContactNameAdapter.KEY_ROWID+" INTEGER PRIMARY KEY AUTOINCREMENT, " +
        ContactNameAdapter.KEY_NAME+" TEXT, " +
        ContactNameAdapter.KEY_BIRTH_DATE+" TEXT);";

    public static final String PhoneNumberTable = "CREATE TABLE "+DATABASE_TABLE2+" (" + 
        PhoneNumberAdapter.KEY_NUMBER+" TEXT , " +
        PhoneNumberAdapter.KEY_DESCRIPTION+" TEXT, " +
        PhoneNumberAdapter.KEY_CONTACTID+" TEXT, " +
        "FOREIGN KEY(" + PhoneNumberAdapter.KEY_CONTACTID +") REFERENCES " +
        (ContactNameAdapter.DATABASE_TABLE)+"("+ContactNameAdapter.KEY_ROWID+") ON DELETE CASCADE"+
    ");";

    static class DbHelper extends SQLiteOpenHelper{
        public DbHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }
        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(ContactNameTable);
            db.execSQL(PhoneNumberTable);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int arg1, int arg2) {
            db.execSQL("DROP TABLE IF EXISTS " + ContactNameAdapter.DATABASE_TABLE);
            db.execSQL("DROP TABLE IF EXISTS " + PhoneNumberAdapter.DATABASE_TABLE);
            onCreate(db);
        }
    }

    public dbAdapter(Activity a){   
        if(!ourConstructorBool == true){
            ourContext = a;
            DATABASE_NAME = a.getString(Asaf.com.contactsEX.R.string.DB_NAME);
            ourConstructorBool = true;
        }
    }

    public dbAdapter open() throws SQLException{
        if(!ourDB == true){
            ourHelper = new DbHelper(ourContext);
            ourDB = true;
        }
        ourDatabase = ourHelper.getWritableDatabase();
        return this;
    }

    public void close(){
        if(ourDatabase.isOpen())
            ourHelper.close();
    }
}

And this is one of my table classes, the rest of the classes are implemented the same, just add as much as you like:

public class PhoneNumberAdapter extends dbAdapter{

    public static final String KEY_NUMBER = "PhoneNumber";
    public static final String KEY_DESCRIPTION = "Description";
    public static final String KEY_CONTACTID = "ContactName_id";

    public static final String DATABASE_TABLE = "PhoneNumber";

    public PhoneNumberAdapter(Activity a){
        super(a);
    }

    public long createEntry(String number, String description,long id){
        // TODO Auto-generated method stub
        ContentValues cv = new ContentValues();
        cv.put(KEY_NUMBER, number);
        cv.put(KEY_DESCRIPTION, description);
        cv.put(KEY_CONTACTID, id);
        return ourDatabase.insert(DATABASE_TABLE, null,cv);
    }
}

Hope I helped.