android 数据库工具类MyDbHelper

package com.tdd.db.util;

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;

public class MyDbHelper {
public static final String KEY_TITLE = "title"; //数据表字段
public static final String KEY_BODY = "body"; //数据表字段
public static final String KEY_ROWID = "_id"; //数据表字段

private DatabaseHelper mDbHelper; //SQLiteOpenHelper实例对象
private SQLiteDatabase mDb; //数据库实例对象

//数据表创建语句
private static final String DATABASE_CREATE = "create table notes (_id integer primary key autoincrement, "
+ "title text not null, body text not null);";

private static final String DATABASE_NAME = "data"; //数据库名
private static final String DATABASE_TABLE = "notes"; //数据库表名
private static final int DATABASE_VERSION = 2; //数据库版本号

private final Context mCtx; //上下文实例

private static class DatabaseHelper extends SQLiteOpenHelper { //数据库辅助类
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) {
db.execSQL("DROP TABLE IF EXISTS notes");
onCreate(db);
}
}

/**
* Constructor - takes the context to allow the database to be opened/created
*
* @param ctx the Context within which to work
*/
public MyDbHelper(Context ctx) {
this.mCtx = ctx;
}

/**
* Open the notes database. If it cannot be opened, try to create a new instance of the database.
* If it cannot be created, throw an exception to signal the failure
*
* @return this (self reference, allowing this to be chained in an initialization call)
* @throws SQLException if the database could be neither opened or created
*/
public MyDbHelper open() throws SQLException {
mDbHelper = new DatabaseHelper(mCtx);
mDb = mDbHelper.getWritableDatabase();
return this;
}

public void close() {
mDbHelper.close();
}


/**
* Create a new note using the title and body provided. If the note is successfully created
* return the new rowId for that note, otherwise return a -1 to indicate failure.
*
* @param title the title of the note
* @param body the body of the note
* @return rowId or -1 if failed
*/
public long createNote(String title, String body) {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_TITLE, title);
initialValues.put(KEY_BODY, body);
return mDb.insert(DATABASE_TABLE, null, initialValues);
}

/**
* Delete the note with the given rowId
*
* @param rowId id of note to delete
* @return true if deleted, false otherwise
*/
public boolean deleteNote(long rowId) {
return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}

/**
* Return a Cursor over the list of all notes in the database
*
* @return Cursor over all notes
*/
public Cursor fetchAllNotes() {
return mDb.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE,KEY_BODY}, null, null, null, null, null);
}

/**
* Return a Cursor positioned at the note that matches the given rowId
*
* @param rowId id of note to retrieve
* @return Cursor positioned to matching note, if found
* @throws SQLException if note could not be found/retrieved
*/
public Cursor fetchNote(long rowId) throws SQLException {

Cursor mCursor = mDb.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,KEY_TITLE,
KEY_BODY}, KEY_ROWID + "=" + rowId, null, null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}

/**
* Update the note using the details provided. The note to be updated is specified using the rowId,
*and it is altered to use the title and body values passed in
*
* @param rowId id of note to update
* @param title value to set note title to
* @param body value to set note body to
* @return true if the note was successfully updated, false otherwise
*/
public boolean updateNote(long rowId, String title, String body) {
ContentValues args = new ContentValues();
args.put(KEY_TITLE, title);
args.put(KEY_BODY, body);
return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}
}