A pre-populated database does not work at API 28 throws no such table exception
The typical cause of an App, that uses SQLite and that copies a pre-existing database suddenly not working for API 28 is that to get around the issue of the database folder not existing (the copy would fail if the directory didn't exist) is to create an empty database and then overwrite the database.
However, as by default, from API 28, the SDK uses WAL (Write-ahead logging) and that creating the empty database to be overwritten, results in the -shm and -wal files being created. It is the existence of these files that result in the database being empty after the copy.
- I believe that this is because once the copied database is opened, a mismach is detected and the SDK's methods create an empty usable database (this is conjecture and hasn't actually been shown to be).
Quick Fix
The quick, but not recommended fix, is to override the onConfigure method in the class that subclasses SQLiteOpenHelper to use the disableWriteAheadLogging method so that the database is opened in journal mode.
- the full code below (2nd piece of code) includes this, but the line has been commented out.
Recommended Fix
The recommended method, so as to gain from the benefits of WAL, is to check for the existence of the database directory and create the directory if it doesn't exist rather than create a database to be overwritten (and therefore the -shm and -wal file don't exist when the database is copied)
The following is an example method where the directory is checked/created when checking to see if the database exists (obviously this would need to be tailored accordingly) :-
private boolean checkDataBase() {
/**
* Does not open the database instead checks to see if the file exists
* also creates the databases directory if it does not exists
* (the real reason why the database is opened, which appears to result in issues)
*/
File db = new File(myContext.getDatabasePath(DB_NAME).getPath()); //Get the file name of the database
if (db.exists()) return true; // If it exists then return doing nothing
// Get the parent (directory in which the database file would be)
File dbdir = db.getParentFile();
// If the directory does not exits then make the directory (and higher level directories)
if (!dbdir.exists()) {
db.getParentFile().mkdirs();
dbdir.mkdirs();
}
return false;
}
- Note that this relies upon the variable DB_NAME being the database name (file name of the database file) and that the final location of the database is the standard location (data/data/the_package/databases/).
The above has been extracted from the following subclass of SQLiteOpenHelper :-
public class DBHelper extends SQLiteOpenHelper {
private static String DB_NAME = "db";
private SQLiteDatabase myDataBase;
private final Context myContext;
private int bytes_copied = 0;
private static int buffer_size = 1024;
private int blocks_copied = 0;
public DBHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
// Check for and create (copy DB from assets) when constructing the DBHelper
if (!checkDataBase()) {
bytes_copied = 0;
blocks_copied = 0;
createDataBase();
}
}
/**
* Creates an empty database on the system and rewrites it with your own database.
* */
public void createDataBase() {
boolean dbExist = checkDataBase(); // Double check
if(dbExist){
//do nothing - database already exists
} else {
//By calling this method an 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();
//<<<<<<<<<< Dimsiss the above comment
//By calling this method an empty database IS NOT created nor are the related -shm and -wal files
//The method that creates the database is flawed and was only used to resolve the issue
//of the copy failing in the absence of the databases directory.
//The dbExist method, now utilised, checks for and creates the database directory, so there
//is then no need to create the database just to create the databases library. As a result
//the -shm and -wal files will not exist and thus result in the error associated with
//Android 9+ failing with due to tables not existining after an apparently successful
//copy.
try {
copyDataBase();
} catch (IOException e) {
File db = new File(myContext.getDatabasePath(DB_NAME).getPath());
if (db.exists()) {
db.delete();
}
e.printStackTrace();
throw new RuntimeException("Error copying database (see stack-trace above)");
}
}
}
/**
* 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() {
/**
* Does not open the database instead checks to see if the file exists
* also creates the databases directory if it does not exists
* (the real reason why the database is opened, which appears to result in issues)
*/
File db = new File(myContext.getDatabasePath(DB_NAME).getPath()); //Get the file name of the database
Log.d("DBPATH","DB Path is " + db.getPath()); //TODO remove for Live App
if (db.exists()) return true; // If it exists then return doing nothing
// Get the parent (directory in which the database file would be)
File dbdir = db.getParentFile();
// If the directory does not exits then make the directory (and higher level directories)
if (!dbdir.exists()) {
db.getParentFile().mkdirs();
dbdir.mkdirs();
}
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 {
final String TAG = "COPYDATABASE";
//Open your local db as the input stream
Log.d(TAG,"Initiated Copy of the database file " + DB_NAME + " from the assets folder."); //TODO remove for Live App
InputStream myInput = myContext.getAssets().open(DB_NAME); // Open the Asset file
String dbpath = myContext.getDatabasePath(DB_NAME).getPath();
Log.d(TAG,"Asset file " + DB_NAME + " found so attmepting to copy to " + dbpath); //TODO remove for Live App
// Path to the just created empty db
//String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
File outfile = new File(myContext.getDatabasePath(DB_NAME).toString());
Log.d("DBPATH","path is " + outfile.getPath()); //TODO remove for Live App
//outfile.setWritable(true); // NOT NEEDED as permission already applies
//OutputStream myoutputx2 = new FileOutputStream(outfile);
/* Note done in checkDatabase method
if (!outfile.getParentFile().exists()) {
outfile.getParentFile().mkdirs();
}
*/
OutputStream myOutput = new FileOutputStream(outfile);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[buffer_size];
int length;
while ((length = myInput.read(buffer))>0) {
blocks_copied++;
Log.d(TAG,"Ateempting copy of block " + String.valueOf(blocks_copied) + " which has " + String.valueOf(length) + " bytes."); //TODO remove for Live App
myOutput.write(buffer, 0, length);
bytes_copied += length;
}
Log.d(TAG,
"Finished copying Database " + DB_NAME +
" from the assets folder, to " + dbpath +
String.valueOf(bytes_copied) + "were copied, in " +
String.valueOf(blocks_copied) + " blocks of size " +
String.valueOf(buffer_size) + "."
); //TODO remove for Live App
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
Log.d(TAG,"All Streams have been flushed and closed."); //TODO remove for Live App
}
@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) {
}
@Override
public void onConfigure(SQLiteDatabase db) {
super.onConfigure(db);
Log.d("DBCONFIGURE","Database has been configured "); //TODO remove for Live App
//db.disableWriteAheadLogging(); //<<<<<<<<<< un-comment to force journal mode
}
@Override
public void onOpen(SQLiteDatabase db) {
super.onOpen(db);
Log.d("DBOPENED","Database has been opened."); //TODO remove for live App
}
}
- Note the above code is/was intended for development/experimentation and thus includes code that could be removed.
Android P - 'SQLite: No Such Table Error' after copying database from assets in android version 9
This is caused because of the use of this.getReadableDatabase() before the copy.
This creates a database and since Android 9 the database is opened, by default, in WAL mode. This results in two files -wal and -shm (each preceded with the database file name) that are owned by the database which is overwritten, not by database that overwrites the former. This anomaly is detected and results in an empty database being returned and hence the table not found.
There are a few get-arounds but the suggested and most efficient way is to not open the database but to instead check if the file exists.
e.g. :-
private boolean checkDB() {
File cDB = new File(con.getDatabasePath(db_name).getPath());
if (cDB.exists()) return true;
if (!cDB.getParentFile().exists()) {
cDB.getParentFile().mkdirs();
}
return false;
}
Note this additionally gets around the issue why opening the database was likely introduced instead of the the file check; that is checking the file, without creating the parent directory (the databases folder) would subsequently fail when attempting the copy of the database file with an ENOENT cannot open file or directory exception.
databases are stored, unless otherwise specified, at data/data/the_package_name/databases/. However, when an App is installed only data/data/package_name/ exists, there is no databases folder/directory.
Opening the database as an SQLiteDatabase is quite expensive resource wise, a fair bit has to be done, the header checked, the schema generated and written to disk or read from disk into memory, the creation of the android_metadata table, the writing to the -wal and -shm files in addition to actually getting a File.
The only flaw as such with this method is that if the asset weren't a valid database in which case a Corrupt Database exception would occur. If this is an issue then you can easily check the first 16 bytes of the header as per Database File Format.
In addition to the above you should also remove/comment out this.getReadableDatabase(); in the createDB method. As this will also result in the same issue.
A more in-depth answer
Android Studio SQLite Could not open database Error
When you instantiate DbHelper as in db = new DbHelper(this); the constructor tries to open the database when it does not exist.
public DbHelper(@Nullable Context context) {
super(context, DB_NAME, null, 1);
assert context != null;
DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
openDataBase(); //<<<<<<<<<< WILL ONLY WORK IF DB EXISTS
this.mContext = context;
}
You could instead use :-
public DbHelper(@Nullable Context context) {
super(context, DB_NAME, null, 1);
assert context != null;
this.mContext = context;
DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
if (!checkDataBase()) {
try {
createDataBase();
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("Unable to Copy Database");
}
}
openDataBase();
}
In which case MainActivity could be :-
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
seekBar = (SeekBar)findViewById(R.id.seekBar);
txtMode= (TextView) findViewById(R.id.txtMode);
btnPlay = (Button)findViewById(R.id.btnPlay);
btnScore = (Button)findViewById(R.id.btnScore);
db = new DbHelper(this);
}
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