SQLite onUpgrade（）令人沮丧

Question

I'm working with a prepopulated database. Using SQLite Manager in Mozilla, right now I have a dummy database and just wanted to test out the onUpgrade method, so I altered a string in one of the columns, exported it as a new database and as you'll see in my code, tried to open the newly updated version. Also important note, I'm updating the version number by one manually in the code

private static final int DB_VERSION = 3;

and in the onUpgrade

if (newVersion == 3) {
        Log.e("WORKED!!", "onUpgrade executed");

so next time I would update these two numbers to 4. Not sure if I'm doing this right or what's wrong but I'm getting the log message, just not seeing the data updated in the app.

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.util.Log;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;


public class DataBaseHelper extends SQLiteOpenHelper {
    private static String DB_PATH;
    private static final String DB_NAME = "DummyTestOne.sqlite";
    private static final int DB_VERSION = 3;
    private static final String DB_NAME2 = "DummyTestFive.sqlite";
    private SQLiteDatabase mDataBase;
    private final Context mContext;

public static final String DBTABLENAME = "questiontable";
public static final String DBATABLENAME = "answertable";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_NAME = "question";
public static final String COLUMN_CATEGORY = "category";
public static final String COLUMN_FID = "fid";

public static final String COLUMN_ANSWER = "answer";

public DataBaseHelper(Context context) {
    super(context, DB_NAME, null, DB_VERSION);
    this.mContext = context;

    DB_PATH = context.getDatabasePath(DB_NAME).getPath();


}

public void createDataBase() {
    boolean dbExist = checkDataBase();

    if (dbExist) {

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

private boolean checkDataBase() {
    SQLiteDatabase checkDB = null;

    try {
        checkDB = SQLiteDatabase.openDatabase(DB_PATH, null, SQLiteDatabase.OPEN_READWRITE);
    } catch (SQLiteException e) {
        Log.e(this.getClass().toString(), "Error while checking db");
    }

    if (checkDB != null) {
        checkDB.close();
    }

    return checkDB != null ? true : false;
}

private void copyDataBase() throws IOException {
    InputStream externalDbStream = mContext.getAssets().open(DB_NAME);
    OutputStream localDbStream = new FileOutputStream(DB_PATH);

    byte[] buffer = new byte[1024];
    int bytesRead;
    while ((bytesRead = externalDbStream.read(buffer)) > 0) {
        localDbStream.write(buffer, 0, bytesRead);
    }


    localDbStream.flush();
    localDbStream.close();
    externalDbStream.close();
}

public void openDataBase() throws SQLException {


    mDataBase = this.getWritableDatabase();

}

@Override
public synchronized void close() {
    if (mDataBase != null) {
        mDataBase.close();
    }
    super.close();
}

public Cursor getCursorForAllQs() {
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
    queryBuilder.setTables(DBTABLENAME);

    String[] asColumnsToReturn = new String[]{COLUMN_ID, COLUMN_NAME, COLUMN_CATEGORY, COLUMN_FID};

    Cursor mCursor = queryBuilder.query(mDataBase, asColumnsToReturn, null,
            null, null, null, "_id");

    return mCursor;
}

public List<String> getAnswersForQ(int questionFid) {
    List<String> answers = new ArrayList<>();
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
    queryBuilder.setTables(DBATABLENAME);
    String[] tableColumns = new String[]{DataBaseHelper.COLUMN_ANSWER};
    String where = "fid = ?";
    String[] selectionArgs = new String[]{String.valueOf(questionFid)};
    String orderBy = DataBaseHelper.COLUMN_ID;


    Cursor c = queryBuilder.query(mDataBase, tableColumns, where, selectionArgs, null, null, orderBy);
    if (c.moveToFirst()) {
        do {
            try{
                answers.add(c.getString(c.getColumnIndex(DataBaseHelper.COLUMN_ANSWER)));
            } catch (Exception e) {
                Log.e("FAILED", c.getString((c.getColumnIndex(DataBaseHelper.COLUMN_ANSWER))));
            }

        } while (c.moveToNext());
    }
    Log.d("getAnswersForQ", answers.toString());
    return answers;

}

public String getName(Cursor c) {
    return (c.getString(1));
}



@Override
public void onCreate(SQLiteDatabase db) {

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    if (newVersion == 3) {
        Log.e("WORKED!!", "onUpgrade executed");
    }
    if (newVersion > oldVersion) {
        InputStream inputStream = null;
        OutputStream outputStream = null;
        String dbFilePath = DB_PATH + DB_NAME;


        try {
            inputStream = mContext.getAssets().open(DB_NAME2);

            outputStream = new FileOutputStream(dbFilePath);

            byte[] buffer = new byte[1024];
            int length;
            while ((length = inputStream.read(buffer)) > 0) {
                outputStream.write(buffer, 0, length);
            }

            outputStream.flush();
            outputStream.close();
            inputStream.close();
        } catch (IOException e) {
            throw new Error("Problem copying database from resource file.");
        }
    }
}
}

Answer 1

Upgrading a database means changing it in place while keeping the old data intact as much as possible. So if you want to add or rename a column, you have to execute the proper SQL command to do this in the onUpgrade callback.

(Note: SQLiteAssetHelper makes using a prepopulated database easier, and you should use it, but upgrading still needs a separate SQL script.)

If you do not care about the contents of the old database, then you should not upgrade it. Just give your new database version a new file name, so that it is simply copied over, and delete the old file.