Android數據庫工作方式解析

在手機系統領域中，谷歌的android操作系統算是一個新起之秀。但是其優秀的性能以及開源性，使其一經推出就伸手廣大用戶的好評。在這裡我們可以從android數據庫的相關操作來體驗這一系統給我們帶來的好處。

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一個好的習慣是創建一個輔助類來簡化你的數據庫交互。

考慮創建一個數據庫適配器，來添加一個與數據庫交互的包裝層。它應該提供直觀的、強類型的方法，如添加、刪除和更新項目。數據庫適配器還應該處理查詢和對創建、打開和關閉數據庫的包裝。

它還常用靜態的android數據庫常量來定義表的名字、列的名字和列的索引。

下面的代碼片段顯示了一個標准數據庫適配器類的框架。它包括一個SQLiteOpenHelper類的擴展類，用於簡化打開、創建和更新android數據庫。

import android.content.Context;  
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 helpe  
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 void close() {  
db.close();  
}  
public long insertEntry(MyObject _myObject) {  
ContentValues contentValues = new ContentValues();  
// TODO fill in ContentValues to represent the new row  
return db.insert(DATABASE_TABLE, null, contentValues);  
}  
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) {  
MyObject objectInstance = new MyObject();  
// TODO Return a cursor to a row from the database and  
// use the values to populate an instance of MyObject  
return objectInstance;  
}  
public int updateEntry(long _rowIndex, MyObject _myObject) {  
String where = KEY_ID + “=” + _rowIndex;  
ContentValues contentValues = new ContentValues();  
// TODO fill in the ContentValue based on the new object  
return db.update(DATABASE_TABLE, contentValues, where, null);  
}  
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  
// to create a new one.  
@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 “ +  
_oldVersion + “ to “ + _newVersion +  
“, which will destroy all old data”);  
// 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);  
}  
}  
} 

android數據庫的相關操作就為大家介紹到這裡。