Every application uses data, and Android applications are no exception. Android uses the open-source, stand-alone SQL database, SQLite. Learn how to create and manipulate a SQLite database for your Android app.
Creating the DBAdapter Helper Class
A good practice for dealing with databases is to create a helper class to encapsulate all the complexities of accessing the database so that it's transparent to the calling code. So, create a helper class called DBAdapter that creates, opens, closes, and uses a SQLite database.
First, add a DBAdapter.java file to the src/<package_name> folder
In the DBAdapter.java file, import all the various namespaces that you will need:
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DBAdapter
{
}
Next, create a database named bookstitles with the fields shown in
| Define the following constants in the DBAdapter.java file. |
|
import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log;
public class DBAdapter { public static final String KEY_ROWID = "_id"; public static final String KEY_ISBN = "isbn"; public static final String KEY_TITLE = "title"; public static final String KEY_PUBLISHER = "publisher"; private static final String TAG = "DBAdapter"; private static final String DATABASE_NAME = "books"; private static final String DATABASE_TABLE = "titles"; private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE = "create table titles (_id integer primary key autoincrement, " + "isbn text not null, title text not null, " + "publisher text not null);"; private final Context context; } |
The DATABASE_CREATE constant contains the SQL statement for creating the titles table within the books database.
| Within the DBAdapter class, you extend the SQLiteOpenHelper class—an Android helper class for database creation and versioning management. In particular, you override the onCreate() and onUpgrade() methods In the DBAdapter class, extend the SQLiteOpenHelper class and override the onCreate() and onUpgrade() methods. |
|
import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log;
public class DBAdapter { public static final String KEY_ROWID = "_id"; public static final String KEY_ISBN = "isbn"; public static final String KEY_TITLE = "title"; public static final String KEY_PUBLISHER = "publisher"; private static final String TAG = "DBAdapter"; private static final String DATABASE_NAME = "books"; private static final String DATABASE_TABLE = "titles"; private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE = "create table titles (_id integer primary key autoincrement, " + "isbn text not null, title text not null, " + "publisher text not null);"; private final Context context; private DatabaseHelper DBHelper; private SQLiteDatabase db;
public DBAdapter(Context ctx) { this.context = ctx; DBHelper = new DatabaseHelper(context); } private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); }
@Override public void onCreate(SQLiteDatabase db) { db.execSQL(DATABASE_CREATE); }
@Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data"); db.execSQL("DROP TABLE IF EXISTS titles"); onCreate(db); } } } |
The onCreate() method creates a new database if the required database is not present. The onUpgrade() method is called when the database needs to be upgraded. This is achieved by checking the value defined in the DATABASE_VERSION constant. For this implementation of the onUpgrade() method, you will simply drop the table and create the table again.
| Defining the various methods for opening and closing the database, as well as the methods for adding/editing/deleting rows in the table. |
| public class DBAdapter { //... //...
//---opens the database--- public DBAdapter open() throws SQLException { db = DBHelper.getWritableDatabase(); return this; }
//---closes the database--- public void close() { DBHelper.close(); } //---insert a title into the database--- public long insertTitle(String isbn, String title, String publisher) { ContentValues initialValues = new ContentValues(); initialValues.put(KEY_ISBN, isbn); initialValues.put(KEY_TITLE, title); initialValues.put(KEY_PUBLISHER, publisher); return db.insert(DATABASE_TABLE, null, initialValues); }
//---deletes a particular title--- public boolean deleteTitle(long rowId) { return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0; }
//---retrieves all the titles--- public Cursor getAllTitles() { return db.query(DATABASE_TABLE, new String[] { KEY_ROWID, KEY_ISBN, KEY_TITLE, KEY_PUBLISHER}, null, null, null, null, null); }
//---retrieves a particular title--- public Cursor getTitle(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] { KEY_ROWID, KEY_ISBN, KEY_TITLE, KEY_PUBLISHER }, KEY_ROWID + "=" + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; }
//---updates a title--- public boolean updateTitle(long rowId, String isbn, String title, String publisher) { ContentValues args = new ContentValues(); args.put(KEY_ISBN, isbn); args.put(KEY_TITLE, title); args.put(KEY_PUBLISHER, publisher); return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0; } } |
Notice that Android uses the Cursor class as a return value for queries. Think of the Cursor as a pointer to the result set from a database query. Using Cursor allows Android to more efficiently manage rows and columns as and when needed. You use a ContentValues object to store key/value pairs. Its put() method allows you to insert keys with values of different data types.
| The full source listing of DBAdapter.java class. |
| package net.learn2develop.Database;
import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log;
public class DBAdapter { public static final String KEY_ROWID = "_id"; public static final String KEY_ISBN = "isbn"; public static final String KEY_TITLE = "title"; public static final String KEY_PUBLISHER = "publisher"; private static final String TAG = "DBAdapter"; private static final String DATABASE_NAME = "books"; private static final String DATABASE_TABLE = "titles"; private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE = "create table titles (_id integer primary key autoincrement, " + "isbn text not null, title text not null, " + "publisher text not null);"; private final Context context; private DatabaseHelper DBHelper; private SQLiteDatabase db;
public DBAdapter(Context ctx) { this.context = ctx; DBHelper = new DatabaseHelper(context); } private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); }
@Override public void onCreate(SQLiteDatabase db) { db.execSQL(DATABASE_CREATE); }
@Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data"); db.execSQL("DROP TABLE IF EXISTS titles"); onCreate(db); } } //---opens the database--- public DBAdapter open() throws SQLException { db = DBHelper.getWritableDatabase(); return this; }
//---closes the database--- public void close() { DBHelper.close(); } //---insert a title into the database--- public long insertTitle(String isbn, String title, String publisher) { ContentValues initialValues = new ContentValues(); initialValues.put(KEY_ISBN, isbn); initialValues.put(KEY_TITLE, title); initialValues.put(KEY_PUBLISHER, publisher); return db.insert(DATABASE_TABLE, null, initialValues); }
//---deletes a particular title--- public boolean deleteTitle(long rowId) { return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0; }
//---retrieves all the titles--- public Cursor getAllTitles() { return db.query(DATABASE_TABLE, new String[] { KEY_ROWID, KEY_ISBN, KEY_TITLE, KEY_PUBLISHER}, null, null, null, null, null); }
//---retrieves a particular title--- public Cursor getTitle(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] { KEY_ROWID, KEY_ISBN, KEY_TITLE, KEY_PUBLISHER }, KEY_ROWID + "=" + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; }
//---updates a title--- public boolean updateTitle(long rowId, String isbn, String title, String publisher) { ContentValues args = new ContentValues(); args.put(KEY_ISBN, isbn); args.put(KEY_TITLE, title); args.put(KEY_PUBLISHER, publisher); return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0; } } |
Using the Database
You are now ready to use the database along with the helper class you've created. In the DatabaseActivity.java file, create an instance of the DBAdapter class:
import android.app.Activity;
import android.os.Bundle;
public class DatabaseActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
}
}
Adding a Title
To add a title into the titles table, use the insertTitle() method of the DBAdapter class:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//---add 2 titles---
db.open();
long id;
id = db.insertTitle(
"0470285818",
"C# 2008 Programmer's Reference",
"Wrox");
id = db.insertTitle(
"047017661X",
"Professional Windows Vista Gadgets Programming",
"Wrox");
db.close();
}
The insertTitle() method returns the ID of the inserted row. If an error occurs during the adding, it returns -1.
If you examine the file system of the Android device/emulator, you can observe that the books database is created under the databases folder
Retrieving All the Titles
| Retrieving all the titles in the titles table with the DBAdapter class' getAllTitles() method: |
|
import android.app.Activity; import android.database.Cursor; import android.os.Bundle; import android.widget.Toast;
public class DatabaseActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); DBAdapter db = new DBAdapter(this);
//---get all titles--- db.open(); Cursor c = db.getAllTitles(); if (c.moveToFirst()) { do { DisplayTitle(c); } while (c.moveToNext()); } db.close(); } } |
The result is returned as a Cursor object. To display all the titles, you first need to call the Cursor object's moveToFirst() method. If it succeeds (which means there is at least one row available), display the details of the title using the DisplayTitle() method (defined below). To move to the next title, call the Cursor object's moveToNext() method:
public void DisplayTitle(Cursor c)
{
Toast.makeText(this,
"id: " + c.getString(0) + "\n" +
"ISBN: " + c.getString(1) + "\n" +
"TITLE: " + c.getString(2) + "\n" +
"PUBLISHER: " + c.getString(3),
Toast.LENGTH_LONG).show();
}
It shows the Toast class displaying one of the titles retrieved from the database.
Retrieving a Single Title
To retrieve a single title using its ID, call the getTitle() method of the DBAdapter class with the ID of the title:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//---get a title---
db.open();
Cursor c = db.getTitle(2);
if (c.moveToFirst())
DisplayTitle(c);
else
Toast.makeText(this, "No title found",
Toast.LENGTH_LONG).show();
db.close();
}
The result is returned as a Cursor object. If a row is returned, display the details of the title using the DisplayTitle() method, else display an error message using the Toast class.
| Updating a Title
Update a particular title by calling the DBAdapter class' updateTitle() method and passing the ID of the title you want to update as well as the values of the new fields. |
| @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); DBAdapter db = new DBAdapter(this);
//---update title--- db.open(); if (db.updateTitle(1, "0470285818", "C# 2008 Programmer's Reference", "Wrox Press")) Toast.makeText(this, "Update successful.", Toast.LENGTH_LONG).show(); else Toast.makeText(this, "Update failed.", Toast.LENGTH_LONG).show(); //------------------- //---retrieve the same title to verify--- Cursor c = db.getTitle(1); if (c.moveToFirst()) DisplayTitle(c); else Toast.makeText(this, "No title found", Toast.LENGTH_LONG).show(); //------------------- db.close(); } |
A message is displayed to indicate if the update is successful. At the same time, you retrieve the title that you have just updated to verify that the update is indeed correct.
Deleting a Title
To delete a title, use the deleteTitle() method in the DBAdapter class by passing the ID of the title you want to delete:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//---delete a title---
db.open();
if (db.deleteTitle(1))
Toast.makeText(this, "Delete successful.",
Toast.LENGTH_LONG).show();
else
Toast.makeText(this, "Delete failed.",
Toast.LENGTH_LONG).show();
db.close();
}
A message is displayed to indicate if the deletion is successful.
