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POCopy pre-populated db from /assets
 

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  1. POCopy pre-populated db from /assets
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    <p>I am using code in <a href="http://www.reigndesign.com/blog/using-your-own-sqlite-database-in-android-applications/" rel="nofollow">this article</a> to copy a pre-populated db I have into a freshly created db thus overwriting it. </p> <p>The overwrite is successful. I am able to see the correctly copied db in the right path data/data/my.package/databases/myDatabase. But this is ONLY if I look at the database before leaving getWritableDatabse().</p> <p>If I leave getWritableDatabse() the db is invalidated: it still keeps its right size BUT it has only the android_metadata instead of my tables that are then all gone. </p> <p>I didn't manage to get access to the Android source code for Eclipse (followed all the instructions but it still doesn't work) but using <a href="http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.0.3_r1/android/database/sqlite/SQLiteOpenHelper.java#SQLiteOpenHelper.getWritableDatabase%28%29" rel="nofollow">GrepCode</a> I managed to narrow down the problem to lines 173-176 in method <code>getWritableDatabase()</code>.</p> <pre><code>173 db.setVersion(mNewVersion); 174 db.setTransactionSuccessful(); 175 } finally { 176 db.endTransaction(); </code></pre> <p>Anyone has a clue why this piece of code might rewrite my db and empty it?</p> <p>This is the relevant stack:</p> <pre><code>Thread [&lt;1&gt; main] (Suspended) StournamentDbAdapter$DatabaseHelper(SQLiteOpenHelper).getWritableDatabase() line: 180 StournamentDbAdapter.open() line: 192 ActivityTournamentsList.onCreate(Bundle) line: 57 ActivityTournamentsList(Activity).performCreate(Bundle) line: 4465 Instrumentation.callActivityOnCreate(Activity, Bundle) line: 1049 ActivityThread.performLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 1920 ActivityThread.handleLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 1981 ActivityThread.access$600(ActivityThread, ActivityThread$ActivityClientRecord, Intent) line: 123 ActivityThread$H.handleMessage(Message) line: 1147 ActivityThread$H(Handler).dispatchMessage(Message) line: 99 Looper.loop() line: 137 ActivityThread.main(String[]) line: 4424 Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method] Method.invoke(Object, Object...) line: 511 ZygoteInit$MethodAndArgsCaller.run() line: 784 ZygoteInit.main(String[]) line: 551 NativeStart.main(String[]) line: not available [native method] </code></pre> <p>I fist use <code>mDb = mDbHelper.getWritableDatabase();</code> which calls to <code>DatabaseHelper.onCreate()</code>where the creation of the db actually happens. In <code>DatabaseHelper.onCreate()</code> I call only <code>copyDatabase();</code> which looks like this:</p> <pre><code>private void copyDatabase() throws IOException { //Open your local db as the input stream InputStream myInput = sContext.getAssets().open(StournamentConstants.Database.DATABASE_NAME); // Path to the just created empty db String outFileName = StournamentConstants.Database.DB_PATH + StournamentConstants.Database.DATABASE_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))&gt;0) { myOutput.write(buffer, 0, length); } //Close the streams myOutput.flush(); myOutput.close(); myInput.close(); } </code></pre> <p>All this goes fine and the db is correctly copied. Only when I climb out of the stack and return to <code>getWritableDatabase() line: 180</code> that something goes wrong: the size of the db stays the same but it loses all tables besides the àndroid_metadata`.</p> <hr> <p><strong>Intermediate conclusion</strong></p> <p>I dug a bit more into the code (the above mentioned GrepCode site was VERY helpful) because I wanted to get to the bottom of this. After going into <code>getWritableDatabase()</code>, on line 165 it will call <code>onCreate()</code>, where I replace to database by using <code>copyDatabase();</code>. The issue is that before, on <code>getWritableDatabase() line 162</code> <code>db.beginTransaction();</code> is called. Why is that a problem? I will explain by showing the sequence of events:</p> <ol> <li>call <code>getWritableDatabase()</code></li> <li><code>getWritableDatabase()</code> calls <code>db = SQLiteDatabase.create(null);</code> hence creating a db</li> <li><code>getWritableDatabase()</code> calls <code>db.beginTransaction();</code></li> <li><code>getWritableDatabase()</code> calls <code>onCreate()</code></li> <li>inside <code>onCreate()</code> I replace the database by calling <code>copyDatabase();</code> which copies the db from asset to the db location. Not sure why the already created db doesn't crash at that moment. Maybe because there is no lock on it?</li> <li>on line 176 <code>getWritableDatabase()</code> calls <code>db.endTransaction();</code> which is the crucial part: it is nice and well that I copied my db into the initially created db, BUT when <code>db.endTransaction();</code> is called, the system commits all the changes to my newly copied db. But remember: I did no changes, I created no tables - I just copied the db to the correct location. So the commit commits NOTHING thus rewriting the db with NOTHING. <strong>For that I get an empty db</strong>.</li> </ol> <p>I had the evil thought to:</p> <ol> <li>Copy the db in <code>onCreate()</code></li> <li>Open the newly copied db and replace the db <code>getWritableDatabase()</code> uses (<code>onCreate()</code> gets the db as parameter from <code>getWritableDatabase()</code>) with it.</li> </ol> <p>Something like that:</p> <pre><code>@Override public void onCreate(SQLiteDatabase db) { try { copyDatabase(); String dbPath = StournamentConstants.Database.DB_PATH + StournamentConstants.Database.DATABASE_NAME; SQLiteDatabase activeDb = SQLiteDatabase.openDatabase(dbPath, null, SQLiteDatabase.OPEN_READONLY); db = activeDb; } catch (IOException e) { Log.i(getClass().getName() + ".onCreate ", e.getMessage()); } } </code></pre> <p>The problem with that is that I get an <code>android.database.sqlite.SQLiteDatabaseLockedException: database is locked</code> so I can't get the newly copied db. And besides that - I am not sure what sinister consequences lurk behind such a devious deed. </p> <p>So I will do what @Barak suggests and move my copying into the constructor - way before the system tries to create the db. So when <code>getWritableDatabase()</code> is finally reached, the db is already there and the system will not attempt to touch it. I learned a lot today - am very pleased.</p> <p>Conclusion: if you can read (code), you have a definite advantage :^) </p> <p>Will keep you posted on how this worked for me. </p> <hr> <p><strong>Final conclusion</strong></p> <p>I solved the issue.</p> <p>Few differences:</p> <ol> <li>I DON'T do it inside <code>DatabaseHelper</code>'s constructor. That would have taken too many code changes. Instead I am doing it inside <code>open()</code> of my <code>private static class DatabaseHelper extends SQLiteOpenHelper</code> class</li> <li>I DON'T use <code>getReadableDatabase()</code> but <code>getWritableDatabase()</code>. The reason is simple: <code>getReadableDatabase()</code> will ALWAYS call <code>getWritableDatabase()</code> so I thought I save that one... </li> </ol> <p>I also tried to be a wiseguy and instead of calling <code>getWritableDatabase()</code> (which has some overhead of code) simply CREATING the db file on my own. I failed. I think it is due to permission issues or something. This is what I tried inside the <code>copyDatabase()</code>:</p> <pre><code>File f = new File(DB_PATH); if (!f.exists()) { f.mkdir(); } </code></pre> <p>But it always fails. I later found out that <code>OutputStream myOutput = new FileOutputStream(outFileName);</code>actually should take care of the file creation.</p> <p>Hope this helps anyone! </p>
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    1. COI do the same thing amenities.works.dine, the problem isn't in the framework. Post your code.
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    2. COConsider using `SQLiteAssetHelper`, which handles the unpack-the-database-from-assets pattern in a reusable component: https://github.com/jgilfelt/android-sqlite-asset-helper
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    3. CO@Barak, added code. Didn't get the amenities.works.dine thing - but it sounds interesting, what did you mean? "Ten remez".
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