An Android helper class to manage database creation and version management using an application's raw asset files.
This class provides developers with a simple way to ship their Android app with an existing SQLite database (which may be pre-populated with data) and to manage its initial creation and any upgrades required with subsequent version releases.
It is implemented as an extension to SQLiteOpenHelper, providing an efficient way for ContentProvider implementations to defer opening and upgrading the database until first use.
Rather than implementing onCreate() and onUpgrade() methods to execute a bunch of SQL statements, developers simply include appropriately named file assets in their project's assets directory. These will include the initial SQLite database file for creation and optionally any SQL upgrade scripts.
Copy android-sqlite-asset-helper.jar into your Android project's libs directory and add it to the build path.
Extend SQLiteAssetHelper as you would normally do SQLiteOpenHelper, providing the constructor with a database name and version number:
public class MyDatabase extends SQLiteAssetHelper {
private static final String DATABASE_NAME = "northwind";
private static final int DATABASE_VERSION = 1;
public MyDatabase(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
}
The name of the database must match a zip compressed file placed in your project's assets/databases directory. This zip file must contain a single SQLite database file. For example:
assets/databases/northwind.zip
The SQLite database file must be the only file within the zip archive. The databse file itself can be named anything you like. ZIP compression is used to minimize APK file size while ensuring that aapt (part of the Android build process) does not corrupt large database files during its own compression process.
The database will be extracted from the assets and copied into place within your application's private data directory. If you prefer to store the database file somewhere else (such as external storage) you can use the alternate constructor to specify a storage path. You must ensure that this path is available and writable whenever your application needs to access the database.
super(context, DATABASE_NAME, context.getExternalFilesDir(null).getAbsolutePath(), null, DATABASE_VERSION);
The database is made available for use the first time either getReadableDatabase() or getWritableDatabase() is called.
The class will throw a SQLiteAssetHelperException if you do not provide the appropriately named file.
The example-v1 project demonstrates a simple database creation and usage example using the classic Northwind database.
At a certain point in your application's lifecycle you will need to alter it's database structure to support additional features. You must ensure users who have installed your app prior to this can safely upgrade their local databases without the loss of any locally held data.
To facilitate a database upgrade, increment the version number that you pass to your SQLiteAssetHelper constructor:
private static final int DATABASE_VERSION = 2;
Update the initial SQLite database in the project's assets/databases directory with the changes and create a text file containing all required SQL commands to upgrade the database from its previous version to it's current version and place it in the same folder. The required naming convention for this upgrade file is as follows:
assets/databases/<database_name>_upgrade_<from_version>-<to_version>.sql
For example, assets/databases/northwind_upgrade_1-2.sql upgrades the database named "northwind" from version 1 to 2. You can include multiple upgrade files to upgrade between any two given versions.
If there are no files to form an upgrade path from a previously installed version to the current one, the class will throw a SQLiteAssetHelperException.
The example-v2 project demonstrates a simple upgrade to the Northwind database which adds a FullName column to the Employee table.
You can use 3rd party tools to automatically generate the SQL required to modify a database from one schema version to another. One such application is SQLite Compare Utility for Windows.
You can force users onto the latest version of the SQLite database (overwriting the local database with the one in the assets) by calling the setForcedUpgradeVersion(int version) method in your constructor. The argument passed is the the version number below which the upgrade will be forced. Note that this will forcibly overwriting any existing local database and all data within it.
Author: Jeff Gilfelt
Contributor: Alexandros Schillings
The code in this project is licensed under the Apache Software License 2.0.
Copyright (c) 2011 readyState Software Ltd.