DB File in Assets Folder. Will it be Updated?

问题:

I'm new to the Android SQLite whole thing. This is what I have:

• I have db.sqlite in my assets folder.
• The intent of the db is to READ ONLY. The user will not write to it.
• When the app gets updated, the db.sqlite will be replaced be a new db (I'll delete the old file from the project and add the new one).

What I'm concerned about is:

• Will the old db file gets deleted? (that's what I want; replacing the old one with the new one)
  • Why ask? Because when I debug my app, each time I update the db file, I need to uninstall the app from the device in order to force the update. Will the users need to do the same when they update my app from the play store? I'm afraid from that.
• Will this be affected by how I implement onCreate(SQLiteDatabase) and onUpgrade(SQLiteDatabase, int, int)?
  • If yes, what is the proper way to implement them to meet my requirement?

This is how I extends the SQLiteOpenHelper class. I followed a tutorial I found in the internet:

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;    
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DataBaseHelper extends SQLiteOpenHelper{

    //The Android's default system path of your application database.
    private static String DB_PATH = "/data/data/com.mydomain.myapp/databases/";
    private static String DB_NAME = "db.sqlite";
    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 DataBaseHelper(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
            Log.i("myapp", "database already exist");
        }else{
            Log.i("myapp", "database NOT exist");

            //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_READWRITE);

    }

    @Override
    public synchronized void close() {

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

            super.close();

    }

    @Override
    public void onCreate(SQLiteDatabase db) {

    }

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

    }

  // My public helper methods to access and get content from the database go here

回答1:

You can't replace database in onUpgrade() because in this method the database is already in use. You have to do it before the database is open, like in a constructor of your DatabaseHelper. As you can't use onUpgrade(), you have to manage database versioning by yourself. Using SharedPreferences is a good way for it. You check if your database exists (if it is already copied from assets directory) and check the version if database exists. Now you can delete old database and copy new one from assets. See implementation below.

To mark your updated application is published with new database in assets just incerment DATABASE_VERSION constant.

private static class DatabaseHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "database.db";
    private static final int DATABASE_VERSION = 1;
    private static final String SP_KEY_DB_VER = "db_ver";
    private final Context mContext;

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        mContext = context;
        initialize();
    }

    /**
     * Initializes database. Creates database if doesn't exist.
     */
    private void initialize() {
        if (databaseExists()) {
            SharedPreferences prefs = PreferenceManager
                    .getDefaultSharedPreferences(mContext);
            int dbVersion = prefs.getInt(SP_KEY_DB_VER, 1);
            if (DATABASE_VERSION != dbVersion) {
                File dbFile = mContext.getDatabasePath(DATABASE_NAME);
                if (!dbFile.delete()) {
                    Log.w(TAG, "Unable to update database");
                }
            }
        }
        if (!databaseExists()) {
            createDatabase();
        }
    }

    /**
     * Returns true if database file exists, false otherwise.
     * @return
     */
    private boolean databaseExists() {
        File dbFile = mContext.getDatabasePath(DATABASE_NAME);
        return dbFile.exists();
    }

    /**
     * Creates database by copying it from assets directory.
     */
    private void createDatabase() {
        String parentPath = mContext.getDatabasePath(DATABASE_NAME).getParent();
        String path = mContext.getDatabasePath(DATABASE_NAME).getPath();

        File file = new File(parentPath);
        if (!file.exists()) {
            if (!file.mkdir()) {
                Log.w(TAG, "Unable to create database directory");
                return;
            }
        }

        InputStream is = null;
        OutputStream os = null;
        try {
            is = mContext.getAssets().open(DATABASE_NAME);
            os = new FileOutputStream(path);

            byte[] buffer = new byte[1024];
            int length;
            while ((length = is.read(buffer)) > 0) {
                os.write(buffer, 0, length);
            }
            os.flush();
            SharedPreferences prefs = PreferenceManager
                    .getDefaultSharedPreferences(mContext);
            SharedPreferences.Editor editor = prefs.edit();
            editor.putInt(SP_KEY_DB_VER, DATABASE_VERSION);
            editor.commit();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (os != null) {
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

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

回答2:

After alot search. I found this- asset folder database is read only. you can't update the database in asset folder. suppose your next app version publish on google play store with new updated database in assert folder. if the name of the both database in assert are same (in previous app and new app) the android system will read old database file only.because file system can't contains two files with same name. What you need to do is just change the name of new database file name in dataOpenhelper.class. like database_1.db .

public class DatabaseOpenHelper extends SQLiteAssetHelper {
    private static final String DATABASE_NAME = "dbbasic_5.db";
    private static final int DATABASE_VERSION = 3;
    private Context contaxtDB;

    // ********* reminder **********
   //  only change database_name = like dbbasic_5.6.7.8  .
    // *******   do not change database_version
    //

    public DatabaseOpenHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        contaxtDB = context;
    }

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

    }


}

回答3:

this one is working fine, try it

public class DatabaseHelper extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 3;
private static final String SP_KEY_DB_VER = "db_ver";
private static final String DATABASE_NAME = "db.db";
private static String DB_PATH = "/data/data/APP_PACKAGE/databases/";
    static SQLiteDatabase db;
    public Context context;

SessionManager session;

    public DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
            this.context = context;
            session = SessionManager.getInstance(context);;
            //initialize();
        }

    public void createDataBase() throws IOException {
            if (!checkDataBase()) {
                getWritableDatabase();
                copyDataBase();
            }
        }

    public boolean checkDataBase() {
            /**/
            boolean found = new File(DB_PATH + DATABASE_NAME).exists();
            if(found)
            {
                int dbVersion = Integer.valueOf(session.getData(SP_KEY_DB_VER, "1"));
                if (DATABASE_VERSION != dbVersion) {
                    File dbFile = context.getDatabasePath(DATABASE_NAME);
                    if (!dbFile.delete()) {
                        Log.w("Warning: ", "Unable to update database");
                    }
                    found = false;
                }
            }
            return found;
        }

        public void copyDataBase() throws IOException {
            InputStream myInput = this.context.getAssets().open(DATABASE_NAME);
            OutputStream myOutput = new FileOutputStream(DB_PATH + DATABASE_NAME);
            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();
            session.saveData(SP_KEY_DB_VER, String.valueOf(DATABASE_VERSION));
            //int dbVersion = prefs.in(SP_KEY_DB_VER, 3);
        }

        public void openDataBase() throws SQLException {
            db = SQLiteDatabase.openDatabase(DB_PATH + DATABASE_NAME, null, 0);
        }
    }

MainActivity -> OnCreate

db = new DatabaseHelper(context);
try {
   db.createDataBase();
} catch (IOException ioe) {
   throw new Error("Unable to create database");
}

db.openDataBase();