Working With Sqlite Databases

It's good practice to create a helper class to simplify your database interactions.

The following section shows you how to create a database adapter class for your database. This abstraction layer encapsulates your database interactions. It will provide intuitive, strongly typed methods for adding, removing, and updating items. A database adapter should also handle queries and expose methods for creating, opening, and closing the database.

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It can also be used as a convenient location to publish static database constants, including table and column names.

Listing 7-1 shows the skeleton code for a standard database adapter class. It includes an extension of the SQLiteOpenHelper class (discussed in more detail in the following section), used to simplify opening, creating, and upgrading the database.

LISTING 7-1: Skeleton code for a standard database adapter implementation Available for download on import android.content.Context;

Wrax.com import android.database.*;

import android.database.sqlite.*;

import android.database.sqlite.SQLiteDatabase.CursorFactory;

import android.util.Log;

public class MyDBAdapter {

private static final String DATABASE_NAME = "myDatabase.db"; private static final String DATABASE_TABLE = "mainTable"; private static final int DATABASE_VERSION = 1;

// The index (key) column name for use in where clauses. public static final String KEY_ID="_id";

// The name and column index of each column in your database, public static final String KEY_NAME="name"; public static final int NAME_COLUMN = 1;

// TODO: Create public field for each column in your table.

// SQL Statement to create a new database.

private static final String DATABASE_CREATE = "create table " + DATABASE_TABLE + " (" + KEY_ID + " integer primary key autoincrement, " + KEY_NAME + " text not null);";

// Variable to hold the database instance private SQLiteDatabase db;

// Context of the application using the database. private final Context context; // Database open/upgrade helper private myDbHelper dbHelper;

public MyDBAdapter(Context _context) { context = _context;

dbHelper = new myDbHelper(context, DATABASE_NAME, null, DATABASE_VERSION);

public MyDBAdapter open() throws SQLException { db = dbHelper.getWritableDatabase(); return this;

public int insertEntry(MyObject _myObject) {

// TODO: Create a new ContentValues to represent my row // and insert it into the database, return index;

public boolean removeEntry(long _rowIndex) {

return db.delete(DATABASE_TABLE, KEY_ID + "=" + _rowIndex, null) > 0;

public Cursor getAllEntries () {

return db.query(DATABASE_TABLE, new String[] {KEY_ID, KEY_NAME}, null, null, null, null, null);

public MyObject getEntry(long _rowIndex) {

// TODO: Return a cursor to a row from the database and // use the values to populate an instance of MyObject return objectInstance;

public boolean updateEntry(long _rowIndex, MyObject _myObject) { // TODO: Create a new ContentValues based on the new object // and use it to update a row in the database. return true;

private static class myDbHelper extends SQLiteOpenHelper {

public myDbHelper(Context context, String name,

CursorFactory factory, int version) { super(context, name, factory, version);

// Called when no database exists in disk and the helper class needs

©Override public void onCreate(SQLiteDatabase _db) { _db.execSQL(DATABASE_CREATE);

// Called when there is a database version mismatch meaning that the version // of the database on disk needs to be upgraded to the current version. ©Override public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion) { // Log the version upgrade.

Log.w("TaskDBAdapter", "Upgrading from version " +

_newVersion + ", which will destroy all old data");

continues

LISTING 7-1 (continued)

// Upgrade the existing database to conform to the new version. Multiple // previous versions can be handled by comparing _oldVersion and _newVersion // values.

// The simplest case is to drop the old table and create a new one. _db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE); // Create a new one. onCreate(_db);

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