I'm using Ormlite has my database for my android application. I have now been given requirements to create a container to be able to hold multiple databases. I do not know before hand how many databases I will need as the number of databases by the container will be dynamic. I've reviewed ormlite's multiple database code, but that is if you know how many databases you have before hand and you create one class per database. I don't have that information available to me. So the question is, how can I create a DatabaseHelper class with ormlite to handle multiple different databases and still be thread safe? All the databases hold the exact same type of data, just different data per container.
DatabaseHelper code:
public class DatabaseHelper extends OrmLiteSqliteOpenHelper {
private static final int DATABASE_VERSION = 1;
private Dao<MyData, Integer> myDataDao;
private static final AtomicInteger usageCounter = new AtomicInteger(0);
private volatile static DatabaseHelper helper = null;
public DatabaseHelper(Context context, String dynamicDBName)
{
super(context, dynamicDBName, null, DATABASE_VERSION);
}
public static DatabaseHelper getHelper(Context context, String dynamicDBName)
{
if (helper == null)
{
synchronized (DatabaseHelper.class)
{
// double check lock to prevent method from being synchronized
// requiring sync lock only being used once
if (helper == null)
helper = new DatabaseHelper(context, dynamicDBName);
}
}
usageCounter.incrementAndGet();
return helper;
}
#Override
public void close()
{
if (usageCounter.decrementAndGet() == 0)
{
super.close();
helper = null;
}
}
}
Related
I have the following DatabaseAccess.java class which contains the following code in order to instance , open , close and some queries :
public class DatabaseAccess {
Context context;
private SQLiteOpenHelper openHelper;
private SQLiteDatabase database;
private static DatabaseAccess instance;
/**
* Private constructor to avoid object creation from outside classes.
*
* #param context
*/
private DatabaseAccess(Context context) {
this.context = context;
this.openHelper = new DatabaseHelper(context);
}
/**
* Return a singleton instance of DatabaseAccess.
*
* #param context the Context
* #return the instance of DabaseAccess
*/
public static DatabaseAccess getInstance(Context context) {
if (instance == null) {
instance = new DatabaseAccess(context);
}
return instance;
}
/**
* Open the database connection.
*/
public void open() {
this.database = openHelper.getWritableDatabase();
}
/**
* Close the database connection.
*/
public void close() {
if (database != null) {
this.database.close();
}
}
However , im getting a serious SONAR warning about this :
Do not place Android context classes in static fields (static
reference to DatabaseAccess which has field context pointing to
Context); this is a memory leak
In my app , every time I need to use databaseAccess instance I do the following on onViewCreated()
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
databaseAccess = DatabaseAccess.getInstance(getContext());
}
I'm really confused about this , how can I fix this memory leak ?
Your getting the error because DatabaseAccess is created with context. And you have it static, so that object is never collected the Garbage. Hence the error.
Instead of passing activity context to the singleton class, you can pass applicationContext(). and #supress the warning
Firstly create an application class for your project like this.
<application android:name="com.xyz.YourApplicataionClassName">
</application>
Then in this application class, create a static getter method for your context.
Call this method wherever you need a context.
public class YourApplicataionClassName extends Application {
private static Context context;
public void onCreate() {
super.onCreate();
YourApplicataionClassName.context = getApplicationContext();
}
public static Context getAppContext() {
return YourApplicataionClassName.context;
}
}
Call YourApplicataionClassName.getAppContext() method and this returns your context.
However using Room Persistence Library is better way then doing all this operations
Have a look at the developer guidelines for implementing databases within Android here. The issue is that you save the context which is a potential memory leak, mentioned by TDIScott. Here is an example how to create it taken from the guidelines:
public class FeedReaderDbHelper extends SQLiteOpenHelper {
// If you change the database schema, you must increment the database version.
public static final int DATABASE_VERSION = 1;
public static final String DATABASE_NAME = "FeedReader.db";
public FeedReaderDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
db.execSQL(SQL_CREATE_ENTRIES);
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// This database is only a cache for online data, so its upgrade policy is
// to simply to discard the data and start over
db.execSQL(SQL_DELETE_ENTRIES);
onCreate(db);
}
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
onUpgrade(db, oldVersion, newVersion);
}
}
If you want a singleton, than do not store the context.
However, I would not recommend to use the SQL Lite implementation directly. ORM libraries or Room specifically are better ways to store data rather than writing the complete boilerplate code around that by yourself. You will find everything you need here.
I am trying to better understand what it means to open an Sqlite database on a background thread in Android. Right now I am using a static/singleton pattern for my database via my class DatabaseHelper, so I only need to open it once, but I want to open it using good practice and understand why I shouldn't open it directly from within my Activity directly (or within the helper's constructor, for example).
My class:
public class DatabaseHelper extends SQLiteOpenHelper {
private static volatile SQLiteDatabase mDatabase;
private static DatabaseHelper mInstance = null;
private static Context mContext;
// ...
public static synchronized DatabaseHelper getInstance(Context context) {
/**
* use the application context as suggested by CommonsWare.
* this will ensure that you don't accidentally leak an Activity's
* context (see this article for more information:
* http://android-developers.blogspot.nl/2009/01/avoiding-memory-leaks.html)
*/
if (mInstance == null) {
mInstance = new DatabaseHelper(context.getApplicationContext());
}
return mInstance;
}
private DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
mContext = context;
}
#Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DB_CREATE_SOME_TABLE); //some SQL expression
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL(DB_ALTER);
}
public void open() throws SQLException {
mDatabase = getWritableDatabase();
}
public void close() {
mDatabase.close();
}
public boolean isOpen() {
return mDatabase.isOpen();
}
//below this would be various CRUD functions operating on mDatabase
// ...
// ...
}
Is it correct to say that you should do something like this:
DatabaseHelper mDatabaseHelper = DatabaseHelper.getInstance(this);
Thread thread = new Thread("OpenDbThread") {
public void run(){
mDatabaseHelper.open();
}
};
thread.start();
inside an Activity somewhere?
You're correct that the code you wrote would open the database on a background thread. However, you wouldn't actually the database was opened until thread.isAlive() returned false (or mDatabase.isOpen() returned true). Alternatively, you could make your Activity listen for a callback from your Thread.
I have two database to support two languages for my application.
I want to change database when I change language from settings.
Is it possible?? How can i do this?
It should be possible quite easily when you provide a string resource with the name of the database:
In /res/values/strings.xml put a line like this:
<string name="db_name">database</string>
In /res/values-de/strings.xml put that line:
<string name="db_name">database_de</string>
And in your DBHelper class use the database name of the strings file currently active according to language settings:
public class DBHelper extends SQLiteOpenHelper {
private final static int DB_VERSION = 1;
private static DBHelper sInstance;
/**
* Provides access to DBHelper singleton.
* #param context
* #return
*/
public static DBHelper getInstance(Context context) {
// Use the application context, which will ensure that you
// don't accidentally leak an Activity's context.
// See this article for more information: http://bit.ly/6LRzfx
if (sInstance == null) {
sInstance = new DBHelper(context.getApplicationContext());
}
return sInstance;
}
/**
* Constructor should be private to prevent direct instantiation.
* make call to static factory method "getInstance()" instead.
*/
private DBHelper(Context context) {
// here comes the magic:
String dbName = context.getString(R.string.db_name);
super(context, db_name, null, 1);
}
#Override
public void onCreate(SQLiteDatabase db) {
// ...
}
// ...
}
using Ridcully solution, you will need to add only the database name part,
all you need to add is the class you extend.
this example from the library you mentioned:
public class MyDatabase extends SQLiteAssetHelper {
private static final int DATABASE_VERSION = 1;
public MyDatabase(Context context) {
// here comes the magic:
String dbName = context.getString(R.string.db_name);
super(context, dbName , null, DATABASE_VERSION);
}
}
The other database class can be:
public class MyDatabase2 extends SQLiteAssetHelper {
private static final int DATABASE_VERSION = 1;
public MyDatabase(Context context) {
// here comes the magic:
String dbName = context.getString(R.string.db_name_2);
super(context, dbName , null, DATABASE_VERSION);
}
}
NOTE: to use SQLiteAssetHelper, u need to create the database yourself, and put in the assets/databases folder.
you can create sqlite database with this app Sqlitebrowser
04-11 05:05:17.837: W/SQLiteConnectionPool(6454): A SQLiteConnection object for database Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.
this is an error return by my logcat ive searched for the possible solution for this error in here andhere saying you should close database but i have this code
#Override
protected void onPause() {
super.onPause();
if (db.isOpen()) {
db.close();
}
}
on all my ativity so im wondering why i get this error
public class DatabaseHelper extends SQLiteOpenHelper {
private static DatabaseHelper sInstance;
private static final String DATABASE_NAME = "database_name";
private static final String DATABASE_TABLE = "table_name";
private static final int DATABASE_VERSION = 1;
public static DatabaseHelper getInstance(Context context) {
// Use the application context, which will ensure that you
// don't accidentally leak an Activity's context.
// See this article for more information: http://bit.ly/6LRzfx
if (sInstance == null) {
sInstance = new DatabaseHelper(context.getApplicationContext());
}
return sInstance;
}
/**
* Constructor should be private to prevent direct instantiation.
* make call to static factory method "getInstance()" instead.
*/
private DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
}
im currently doing the same thing im doing this tutorial if you want to try it you can you can find it here
I've implemented access to a database using SQLiteOpenHelper from the android.database package within some classes (with pattern DAO).
I wrote some junit tests for these classes using an AndroidTestCase but this causes the tests to use the same database as the application.
I read that the ProviderTestCase2 or RenamingDelegatingContext can be used to test the database separately. Unluckily I couldn't find any nice tutorial/example that shows how to test a database with ProviderTestCase2/RenamingDelegatingContext.
Can anyone point me somewhere OR give me some tip OR share some code for database testing?!
Cheeerrrrsss!!
Giorgio
Both the ProviderTestCase and RenamingDelegatingContext will destroy the database if one already exists before opening it within it's context, so in that sense they both have the same low-level approach towards opening a SQLite database.
You leverage this by opening the database in your fixture in setUp(), which will then ensure that your working with a fresh database before each test case.
I would suggest that you go for writing content providers rather than creating database adapters. You can use a common interface for accessing data, be it stored in the DB or somewhere over the network, the design of content providers can be accommodated to access such data at the cost of a bit of IPC overhead involved that most of us shouldn't have to care about.
If you did this for accessing a SQLite database, the framework would completely manage the database connection for you in a separate process. As added beef, the ProviderTestCase2<ContentProvider> completely bootstraps a test context for your content provider without you having to a write a single line of code.
But, that's not said it isn't such a huge effort to do the bootstrapping yourself. So supposing you had a database adapter as such; we'll just focus on open() for getting write access to our database, nothing fancy:
public class MyAdapter {
private static final String DATABASE_NAME = "my.db";
private static final String DATABASE_TABLE = "table";
private static final int DATABASE_VERSION = 1;
/**
* Database queries
*/
private static final String DATABASE_CREATE_STATEMENT = "some awesome create statement";
private final Context mCtx;
private SQLiteDatabase mDb;
private DatabaseHelper mDbHelper;
private static class DatabaseHelper extends SQLiteOpenHelper {
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
#Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DATABASE_CREATE_STATEMENT);
}
#Override
public void onUpgrade(SQLiteDatabase db, int a, int b) {
// here to enable this code to compile
}
}
/**
* Constructor - takes the provided context to allow for the database to be
* opened/created.
*
* #param context the Context within which to work.
*/
public MyAdapter(Context context) {
mCtx = context;
}
/**
* Open the last.fm database. If it cannot be opened, try to create a new
* instance of the database. If it cannot be created, throw an exception to
* signal the failure.
*
* #return this (self reference, allowing this to be chained in an
* initialization call)
* #throws SQLException if the database could be neither opened or created
*/
public MyAdapter open() throws SQLException {
mDbHelper = new DatabaseHelper(mCtx);
mDb = mDbHelper.getWritableDatabase();
return this;
}
public void close() {
mDbHelper.close();
}
}
Then you could write your test as such:
public final class MyAdapterTests extends AndroidTestCase {
private static final String TEST_FILE_PREFIX = "test_";
private MyAdapter mMyAdapter;
#Override
protected void setUp() throws Exception {
super.setUp();
RenamingDelegatingContext context
= new RenamingDelegatingContext(getContext(), TEST_FILE_PREFIX);
mMyAdapter = new MyAdapter(context);
mMyAdapter.open();
}
#Override
protected void tearDown() throws Exception {
super.tearDown();
mMyAdapter.close();
mMyAdapter = null;
}
public void testPreConditions() {
assertNotNull(mMyAdapter);
}
}
So what's happening here is that the context implementation of RenamingDelegatingContext, once MyAdapter(context).open() is called, will always recreate the database. Each test you write now will be going against the state of the database after MyAdapter.DATABASE_CREATE_STATEMENT is called.
I actually use database with SQLiteOpenHelper and I have a trick for testing.
The idea is to use standard on-file stored DB during the normal use of the app and an in-memory DB during tests. In this way you can use a clear DB for each test without insert/delete/update data in your standard DB. It works fine for me.
Keep in mind you can use in-memory database, just passing null as name of database file. This is clearly documented in the API documentation.
Advantages of using in-memory DB during tests is explained here:
https://attakornw.wordpress.com/2012/02/25/using-in-memory-sqlite-database-in-android-tests/
In my project I have the DBHelper class wich extends SQLiteHelper. As you can see, there are the standard methods. I simply added a constructor with two parameters. The difference is that when I call the super constructor, I pass null as DB name.
public class DBHelper extends SQLiteOpenHelper {
public static final int DATABASE_VERSION = 1;
public static final String DATABASE_NAME = "mydatabase.db";
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public DBHelper(Context context, boolean testMode) {
super(context, null, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
//create statements
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//on upgrade policy
}
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//on downgrade policy
}
}
Every "model" in the project extends DBModel that is an abstract class.
public abstract class DBModel {
protected DBHelper dbhelper;
public DBModel(Context context) {
dbhelper = new DBHelper(context);
}
//other declarations and utility function omitted
}
As discussed here: How can I find out if code is running inside a JUnit test or not?
there is a way to establish if you are running JUnit tests, simply searching in stack trace elements.
As a conseguence, I modified DBModel constructor
public abstract class DBModel {
protected DBHelper dbhelper;
public DBModel(Context context) {
if(isJUnitTest()) {
dbhelper = new DBHelper(context, true);
} else {
dbhelper = new DBHelper(context);
}
}
private boolean isJUnitTest() {
StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();
List<StackTraceElement> list = Arrays.asList(stackTrace);
for (StackTraceElement element : list) {
if (element.getClassName().startsWith("junit.")) {
return true;
}
}
return false;
}
//other declarations and utility function omitted
}
Note that
startsWith("junit.")
may be
startsWith("org.junit.")
in your case.
I have an application that uses a ContentProvider backed by an sqlite database to provide data to the application.
Let PodcastDataProvider be the actual dataprovider used by the application.
Then you can set up a test provider with something like the following:
public abstract class AbstractPodcastDataProvider extends ProviderTestCase2<PodcastDataProvider>{
public AbstractPodcastDataProvider(){
this(PodcastDataProvider.class, Feed.BASE_AUTH);
}
public AbstractPodcastDataProvider(Class<PodcastDataProvider> providerClass,
String providerAuthority) {
super(providerClass, providerAuthority);
}
public void setUp() throws Exception{
super.setUp();
//clear out all the old data.
PodcastDataProvider dataProvider =
(PodcastDataProvider)getMockContentResolver()
.acquireContentProviderClient(Feed.BASE_AUTH)
.getLocalContentProvider();
dataProvider.deleteAll();
}
}
to setup a test data provider that will be backed by a different database than the actual application.
To test the DAO, create another class which extends AbstractPodcastDataProvider and use the
getMockContentResolver();
method to get an instance of a content resolver that will use the test database instead of the application database.
private static String db_path = "/data/data/android.testdb/mydb";
private SQLiteDatabase sqliteDatabase = null;
private Cursor cursor = null;
private String[] fields;
/*
* (non-Javadoc)
*
* #see dinota.data.sqlite.IDataContext#getSQLiteDatabase()
*/
public SQLiteDatabase getSQLiteDatabase() {
try {
sqliteDatabase = SQLiteDatabase.openDatabase(db_path, null,
SQLiteDatabase.OPEN_READWRITE);
sqliteDatabase.setVersion(1);
sqliteDatabase.setLocale(Locale.getDefault());
sqliteDatabase.setLockingEnabled(true);
return sqliteDatabase;
} catch (Exception e) {
return null;
}
}
if you give the exact location of the sqlite db(in my case it's db_path), using the above method you can find-out whether it returns an sqlitedatabase or not.
A possible solution can be to open database using this method
myDataBase = SQLiteDatabase.openDatabase(DATABASE_NAME, null, SQLiteDatabase.OPEN_READWRITE);
And change database name in your tests. Here you can find some info about this method.