What are the best practices for SQLite on Android?

Question

What would be considered the best practices when executing queries on an SQLite database within an Android app?

Is it safe to run inserts, deletes and select queries

Answer 1

• Use a Thread or AsyncTask for long-running operations (50ms+). Test your app to see where that is. Most operations (probably) don't require a thread, because most operations (probably) only involve a few rows. Use a thread for bulk operations.
• Share one SQLiteDatabase instance for each DB on disk between threads and implement a counting system to keep track of open connections.

Are there any best practices for these scenarios?

Share a static field between all your classes. I used to keep a singleton around for that and other things that need to be shared. A counting scheme (generally using AtomicInteger) also should be used to make sure you never close the database early or leave it open.

My solution:

The old version I wrote is available at https://github.com/Taeluf/dev/tree/main/archived/databasemanager and is not maintained. If you want to understand my solution, look at the code and read my notes. My notes are usually pretty helpful.

1. copy/paste the code into a new file named DatabaseManager. (or download it from github)
2. extend DatabaseManager and implement onCreate and onUpgrade like you normally would. You can create multiple subclasses of the one DatabaseManager class in order to have different databases on disk.
3. Instantiate your subclass and call getDb() to use the SQLiteDatabase class.
4. Call close() for each subclass you instantiated

The code to copy/paste:

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;

import java.util.concurrent.ConcurrentHashMap;

/** Extend this class and use it as an SQLiteOpenHelper class
 *
 * DO NOT distribute, sell, or present this code as your own. 
 * for any distributing/selling, or whatever, see the info at the link below
 *
 * Distribution, attribution, legal stuff,
 * See https://github.com/JakarCo/databasemanager
 * 
 * If you ever need help with this code, contact me at support@androidsqlitelibrary.com (or support@jakar.co )
 * 
 * Do not sell this. but use it as much as you want. There are no implied or express warranties with this code. 
 *
 * This is a simple database manager class which makes threading/synchronization super easy.
 *
 * Extend this class and use it like an SQLiteOpenHelper, but use it as follows:
 *  Instantiate this class once in each thread that uses the database. 
 *  Make sure to call {@link #close()} on every opened instance of this class
 *  If it is closed, then call {@link #open()} before using again.
 * 
 * Call {@link #getDb()} to get an instance of the underlying SQLiteDatabse class (which is synchronized)
 *
 * I also implement this system (well, it's very similar) in my Android SQLite Libray at http://androidslitelibrary.com
 * 
 *
 */
abstract public class DatabaseManager {
    
    /**See SQLiteOpenHelper documentation
    */
    abstract public void onCreate(SQLiteDatabase db);
    /**See SQLiteOpenHelper documentation
     */
    abstract public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion);
    /**Optional.
     * *
     */
    public void onOpen(SQLiteDatabase db){}
    /**Optional.
     * 
     */
    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
    /**Optional
     * 
     */
    public void onConfigure(SQLiteDatabase db){}



    /** The SQLiteOpenHelper class is not actually used by your application.
     *
     */
    static private class DBSQLiteOpenHelper extends SQLiteOpenHelper {

        DatabaseManager databaseManager;
        private AtomicInteger counter = new AtomicInteger(0);

        public DBSQLiteOpenHelper(Context context, String name, int version, DatabaseManager databaseManager) {
            super(context, name, null, version);
            this.databaseManager = databaseManager;
        }

        public void addConnection(){
            counter.incrementAndGet();
        }
        public void removeConnection(){
            counter.decrementAndGet();
        }
        public int getCounter() {
            return counter.get();
        }
        @Override
        public void onCreate(SQLiteDatabase db) {
            databaseManager.onCreate(db);
        }

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

        @Override
        public void onOpen(SQLiteDatabase db) {
            databaseManager.onOpen(db);
        }

        @Override
        public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            databaseManager.onDowngrade(db, oldVersion, newVersion);
        }

        @Override
        public void onConfigure(SQLiteDatabase db) {
            databaseManager.onConfigure(db);
        }
    }

    private static final ConcurrentHashMap dbMap = new ConcurrentHashMap();

    private static final Object lockObject = new Object();


    private DBSQLiteOpenHelper sqLiteOpenHelper;
    private SQLiteDatabase db;
    private Context context;

    /** Instantiate a new DB Helper. 
     * 
 SQLiteOpenHelpers are statically cached so they (and their internally cached SQLiteDatabases) will be reused for concurrency
     *
     * @param context Any {@link android.content.Context} belonging to your package.
     * @param name The database name. This may be anything you like. Adding a file extension is not required and any file extension you would like to use is fine.
     * @param version the database version.
     */
    public DatabaseManager(Context context, String name, int version) {
        String dbPath = context.getApplicationContext().getDatabasePath(name).getAbsolutePath();
        synchronized (lockObject) {
            sqLiteOpenHelper = dbMap.get(dbPath);
            if (sqLiteOpenHelper==null) {
                sqLiteOpenHelper = new DBSQLiteOpenHelper(context, name, version, this);
                dbMap.put(dbPath,sqLiteOpenHelper);
            }
            //SQLiteOpenHelper class caches the SQLiteDatabase, so this will be the same SQLiteDatabase object every time
            db = sqLiteOpenHelper.getWritableDatabase();
        }
        this.context = context.getApplicationContext();
    }
    /**Get the writable SQLiteDatabase
     */
    public SQLiteDatabase getDb(){
        return db;
    }

    /** Check if the underlying SQLiteDatabase is open
     *
     * @return whether the DB is open or not
     */
    public boolean isOpen(){
        return (db!=null&&db.isOpen());
    }


    /** Lowers the DB counter by 1 for any {@link DatabaseManager}s referencing the same DB on disk
     *  
If the new counter is 0, then the database will be closed.
     *  

This needs to be called before application exit.
     * 
If the counter is 0, then the underlying SQLiteDatabase is null until another DatabaseManager is instantiated or you call {@link #open()}
     *
     * @return true if the underlying {@link android.database.sqlite.SQLiteDatabase} is closed (counter is 0), and false otherwise (counter > 0)
     */
    public boolean close(){
        sqLiteOpenHelper.removeConnection();
        if (sqLiteOpenHelper.getCounter()==0){
            synchronized (lockObject){
                if (db.inTransaction())db.endTransaction();
                if (db.isOpen())db.close();
                db = null;
            }
            return true;
        }
        return false;
    }
    /** Increments the internal db counter by one and opens the db if needed
    *
    */
    public void open(){
        sqLiteOpenHelper.addConnection();
        if (db==null||!db.isOpen()){
                synchronized (lockObject){
                    db = sqLiteOpenHelper.getWritableDatabase();
                }
        } 
    }
}