Setting up a database in Android

Question

The official Android developer website first mentions that we have to first 'define a schema and contract', which is something like this:

public static abstract class FeedEntry implements BaseColumns {
public static final String TABLE_NAME = "entry";
public static final String COLUMN_NAME_ENTRY_ID = "entryid";
public static final String COLUMN_NAME_TITLE = "title";
public static final String COLUMN_NAME_SUBTITLE = "subtitle";
...

}

The second step mentioned is to 'Create a Database Using a SQL Helper'.

But all the tutorials I have seen on the web directly create a class using 'helper'; For example. Which is the correct way? Both?

Also, should I define and create my database in the main Activity or create a separate Activity for the database?

Answer 1

Create database in SQLite browser (like SQLite Maestro), copy your database in assets folder in your project. Call createDatabase() method in your MainActivity (which is first in your app, launcher activity).

private void createDataBase(){
    DataBaseHelper db = new DataBaseHelper(this);
    try {
        db.createDataBase();
    } catch (IOException e) {
        e.printStackTrace();
    }finally{
        db.close();
    }
}

And helper class:

public class DataBaseHelper extends SQLiteOpenHelper{   

    private static String DB_PATH = "/data/data/your.package/databases/";   
    private static String DB_NAME = "YourDataBaseName.sqlite";
    private static int DB_VERSION = 1;

    private static short WRITE_BUFFER_SIZE = 8192;

    private Context context;

    /**
     * Constructor
     * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
     * @param context Current application context
     */
    public DataBaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);

        this.context = context;
    }   

  /**
     * Creates a empty database on the system and rewrites it with your own database.
     * */
    public synchronized void createDataBase() throws IOException{

        boolean dbExist = checkDataBase();

        if(dbExist){
            //do nothing - database already exist
        }
        else
        {
            //By calling this method and empty database will be created into the default system path
               //of your application so we are gonna be able to overwrite that database with our database.
            this.getWritableDatabase();

            try {
                copyDataBase();
            } catch (IOException e) {
                throw new Error("Error copying database");
            }

        }
    }

    /**
     * Check if the database already exist to avoid re-copying the file each time you open the application.
     * @return true if it exists, false if it doesn't
     */
    private boolean checkDataBase(){
        SQLiteDatabase checkDB = null;
        try{
            String myPath = DB_PATH + DB_NAME;

            checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS);
        }catch(SQLException e){
            e.printStackTrace();
            //database does't exist yet.
        }catch(Exception e){
            e.printStackTrace();
        }

        if(checkDB != null){
            if(checkDB.getVersion() < DB_VERSION){
                checkDB.close();
                return false;
            }else{ 
                checkDB.close();
                return true;
            }
        }

        return false;
    }

    /**
     * Copies your database from your local assets-folder to the just created empty database in the
     * system folder, from where it can be accessed and handled.
     * This is done by transfering bytestream.
     */
    private void copyDataBase() throws IOException{     
        //Open your local db as the input stream    
        InputStream myInput = context.getAssets().open(DB_NAME);

        // Path to the just created empty db
        String outFileName = DB_PATH + DB_NAME;

        //Open the empty db as the output stream
        OutputStream myOutput = new FileOutputStream(outFileName);

        //transfer bytes from the inputfile to the outputfile
        byte[] buffer = new byte[WRITE_BUFFER_SIZE];
        int length;
        while ((length = myInput.read(buffer)) > 0){
            myOutput.write(buffer, 0, length);
        }
        //Close the streams
        myOutput.flush();
        myOutput.close();
        myInput.close();
        this.getWritableDatabase().close();
    }

    @Override
    public synchronized void close() {
            super.close();
    }

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

    @Override
    public void onCreate(SQLiteDatabase db) {   
    }

    /**
     * Delete database and create new one or copy from assets if exists.
     */
    public void clearDatabase(){      
        context.deleteDatabase(DB_NAME);
        try {
            createDataBase();
        } catch (IOException e) {
            e.printStackTrace();
        }

        this.getWritableDatabase().close();
    }
}