-Deprecating database get instance without context.

-Added comments to migrations.

app/src/main/java/org/schabi/newpipe/NewPipeDatabase.java

@@ -21,10 +21,12 @@ public final class NewPipeDatabase {
         databaseInstance = Room
                 .databaseBuilder(context.getApplicationContext(), AppDatabase.class, DATABASE_NAME)
                 .addMigrations(MIGRATION_11_12)
+                .fallbackToDestructiveMigration()
                 .build();
     }
 
     @NonNull
+    @Deprecated
     public static AppDatabase getInstance() {
         if (databaseInstance == null) throw new RuntimeException("Database not initialized");
 

app/src/main/java/org/schabi/newpipe/database/Migrations.java

@@ -12,6 +12,14 @@ public class Migrations {
     public static final Migration MIGRATION_11_12 = new Migration(DB_VER_11_0, DB_VER_12_0) {
         @Override
         public void migrate(@NonNull SupportSQLiteDatabase database) {
+            /*
+            * Unfortunately these queries must be hardcoded due to the possibility of
+            * schema and names changing at a later date, thus invalidating the older migration
+            * scripts if names are not hardcoded.
+            * */
+
+            // Not much we can do about this, since room doesn't create tables before migration.
+            // It's either this or blasting the entire database anew.
             database.execSQL("CREATE TABLE IF NOT EXISTS `streams` (`uid` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `service_id` INTEGER NOT NULL, `url` TEXT, `title` TEXT, `stream_type` TEXT, `duration` INTEGER, `uploader` TEXT, `thumbnail_url` TEXT)");
             database.execSQL("CREATE UNIQUE INDEX `index_streams_service_id_url` ON `streams` (`service_id`, `url`)");
             database.execSQL("CREATE TABLE IF NOT EXISTS `stream_history` (`stream_id` INTEGER NOT NULL, `access_date` INTEGER NOT NULL, PRIMARY KEY(`stream_id`, `access_date`), FOREIGN KEY(`stream_id`) REFERENCES `streams`(`uid`) ON UPDATE CASCADE ON DELETE CASCADE )");