resetting pre-populated sqlite database in android

Question

I added a pre-populated database to the assets directory in an Android App, but when I delete and add a new one the query results still return old data.

I followed this tutorial , and below is my database class:

package com.example.fishselector;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.HashMap;

import android.content.ContentValues;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

class DB extends SQLiteOpenHelper {

    private static String DB_PATH = "/data/data/com.example.fishselector/databases/";

    private static String DB_NAME = "sqldb3";

    private SQLiteDatabase myDataBase;

    private final Context myContext;

    /**
     * Constructor
     * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
     * @param context
     */
    public DB(Context context) {

        super(context, DB_NAME, null, 1);
        this.myContext = context;
    }

    /**
     * Creates a empty database on the system and rewrites it with your own database.
     * */
    public 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.getReadableDatabase();

            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.OPEN_READONLY);

        } catch (SQLiteException e) {

            //database does't exist yet.

        }

        if (checkDB != null) {

            checkDB.close();

        }

        return checkDB != null ? true : 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 = myContext.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[1024];
        int length;
        while ((length = myInput.read(buffer)) > 0) {
            myOutput.write(buffer, 0, length);
        }

        //Close the streams
        myOutput.flush();
        myOutput.close();
        myInput.close();

    }

    public void openDataBase() throws SQLException {

        //Open the database
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

    }

    @
    Override
    public synchronized void close() {

        if (myDataBase != null)
            myDataBase.close();

        super.close();

    }

    @
    Override
    public void onCreate(SQLiteDatabase db) {

        try {
            createDataBase();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


    }

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

    }

    // Add your public helper methods to access and get content from the database.
    // You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
    // to you to create adapters for your views.

}

Answer 1

It's not working because you are not deleting the database file on the file system.

What your code does is copy the file from assets into the private storage area for your app in /data/data/com.example.fishselector/databases/ .

Then the next time you run it you check if it already exists there, and if it does, do nothing:

boolean dbExist = checkDataBase();

if (dbExist) {
    //do nothing - database already exist
} else {

So simply deleting it or replacing it in assets won't mean a thing because hey ho, there it still is, in /data/data/ as if nothing happened.

To fix: in your emulator, go into " Settings/Apps/YourApp/ " and click " Clear Data ". This will delete any data in the private storage area for your app. Then you can try and run your app again and it will not find the file and will copy your new database over from assets .