CP_master-Notes/java/net/micode/notes/data/NotesDatabaseHelper.java

/*
 * Copyright (c) 2010-2011, The MiCode Open Source Community (www.micode.net)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.micode.notes.data;

import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

import net.micode.notes.data.Notes.DataColumns;
import net.micode.notes.data.Notes.DataConstants;
import net.micode.notes.data.Notes.NoteColumns;

/**
 * 1.作用：笔记应用数据库辅助类
 * 2.用处：管理 SQLite 数据库的创建、版本升级和表结构定义
 *      实现了单例模式以确保全局唯一数据库实例
 */
public class NotesDatabaseHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "note.db";

    private static final int DB_VERSION = 4;

    /**
     * 1.作用：表名接口定义
     * 2.内容：包含笔记表 (note) 和数据内容表 (data)
     */
    public interface TABLE {
        public static final String NOTE = "note";

        public static final String DATA = "data";
    }

    private static final String TAG = "NotesDatabaseHelper";

    private static NotesDatabaseHelper mInstance;

    /**
     * 1.作用：创建笔记主表结构
     * 2.变量名：CREATE_NOTE_TABLE_SQL
     * 3.类型：String
     * 3.功能：
     *      存储笔记基本信息和元数据
     *      支持文件夹嵌套结构
     *      自动记录创建 / 修改时间
     *      关联桌面小部件和同步功能
     */
    private static final String CREATE_NOTE_TABLE_SQL =
        "CREATE TABLE " + TABLE.NOTE + "(" +
            NoteColumns.ID + " INTEGER PRIMARY KEY," +
            NoteColumns.PARENT_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.ALERTED_DATE + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.BG_COLOR_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.CREATED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +
            NoteColumns.HAS_ATTACHMENT + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.MODIFIED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +
            NoteColumns.NOTES_COUNT + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.SNIPPET + " TEXT NOT NULL DEFAULT ''," +
            NoteColumns.TYPE + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.WIDGET_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.WIDGET_TYPE + " INTEGER NOT NULL DEFAULT -1," +
            NoteColumns.SYNC_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.LOCAL_MODIFIED + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.ORIGIN_PARENT_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.GTASK_ID + " TEXT NOT NULL DEFAULT ''," +
            NoteColumns.VERSION + " INTEGER NOT NULL DEFAULT 0" +
        ")";

    /**
     * 1.作用：创建笔记内容表结构
     * 2.变量名：CREATE_DATA_TABLE_SQL
     * 3.类型：String
     * 4.功能：
     *      存储不同类型的笔记内容
     *      支持一对多关系（一个笔记可包含多个内容项）
     *      通用字段设计（DATA1-DATA5）适配不同类型数据
     */
    private static final String CREATE_DATA_TABLE_SQL =
        "CREATE TABLE " + TABLE.DATA + "(" +
            DataColumns.ID + " INTEGER PRIMARY KEY," +
            DataColumns.MIME_TYPE + " TEXT NOT NULL," +
            DataColumns.NOTE_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.CREATED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +
            NoteColumns.MODIFIED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +
            DataColumns.CONTENT + " TEXT NOT NULL DEFAULT ''," +
            DataColumns.DATA1 + " INTEGER," +
            DataColumns.DATA2 + " INTEGER," +
            DataColumns.DATA3 + " TEXT NOT NULL DEFAULT ''," +
            DataColumns.DATA4 + " TEXT NOT NULL DEFAULT ''," +
            DataColumns.DATA5 + " TEXT NOT NULL DEFAULT ''" +
        ")";

    /**
     * 1.作用：优化笔记内容查询性能
     * 2.变量名：CREATE_DATA_NOTE_ID_INDEX_SQL
     * 3.类型：String
     * 4.功能：
     *      加速通过笔记 ID 查询相关内容的操作
     *      减少 JOIN 操作时的全表扫描
     *      提升批量数据查询效率
     */
    private static final String CREATE_DATA_NOTE_ID_INDEX_SQL =
        "CREATE INDEX IF NOT EXISTS note_id_index ON " +
        TABLE.DATA + "(" + DataColumns.NOTE_ID + ");";

    /**
     * Increase folder's note count when move note to the folder
     */

    /**
     * 1. 笔记文件夹计数触发器：
     * 2.作用：更新笔记父文件夹时自动维护文件夹的笔记数量统计
     * 3.功能描述：
     * - 当笔记的父文件夹(parent_id)发生变更时，自动增加新父文件夹的笔记计数
     * - 触发器在UPDATE操作后执行，确保计数更新与数据变更同步
     * - 通过维护冗余计数字段，避免频繁执行代价高昂的COUNT(*)查询
     */
    private static final String NOTE_INCREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER increase_folder_count_on_update "+
        " AFTER UPDATE OF " + NoteColumns.PARENT_ID + " ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + " + 1" +
        "  WHERE " + NoteColumns.ID + "=new." + NoteColumns.PARENT_ID + ";" +
        " END";

    /**
     * Decrease folder's note count when move note from folder
     */
    /**
     * 1.作用：维护笔记文件夹计数的完整性
     * 2.变量名：NOTE_DECREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当笔记移动到新文件夹时，减少原文件夹的笔记计数
     *      确保文件夹中的笔记数量统计始终保持准确
     *      防止计数出现负值，通过条件检查确保计数≥0
     */
    private static final String NOTE_DECREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER decrease_folder_count_on_update " +
        " AFTER UPDATE OF " + NoteColumns.PARENT_ID + " ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + "-1" +
        "  WHERE " + NoteColumns.ID + "=old." + NoteColumns.PARENT_ID +
        "  AND " + NoteColumns.NOTES_COUNT + ">0" + ";" +
        " END";

    /**
     * Increase folder's note count when insert new note to the folder
     */

    /**
     * 1.作用：维护笔记文件夹计数的实时性和准确性
     * 2.变量名：NOTE_INCREASE_FOLDER_COUNT_ON_INSERT_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当新笔记创建时，自动增加其父文件夹的笔记计数
     *      确保文件夹中的笔记数量统计始终保持准确
     *      避免手动维护计数可能导致的数据不一致问题
     */

    private static final String NOTE_INCREASE_FOLDER_COUNT_ON_INSERT_TRIGGER =
        "CREATE TRIGGER increase_folder_count_on_insert " +
        " AFTER INSERT ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + " + 1" +
        "  WHERE " + NoteColumns.ID + "=new." + NoteColumns.PARENT_ID + ";" +
        " END";

    /**
     * Decrease folder's note count when delete note from the folder
     */

    /**
     * 1.作用：维护笔记文件夹计数的完整性
     * 2.变量名：NOTE_DECREASE_FOLDER_COUNT_ON_DELETE_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当笔记被删除时，自动减少其父文件夹的笔记计数
     *      确保文件夹中的笔记数量统计始终保持准确
     *      通过条件检查防止计数出现负值
     */
    private static final String NOTE_DECREASE_FOLDER_COUNT_ON_DELETE_TRIGGER =
        "CREATE TRIGGER decrease_folder_count_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + "-1" +
        "  WHERE " + NoteColumns.ID + "=old." + NoteColumns.PARENT_ID +
        "  AND " + NoteColumns.NOTES_COUNT + ">0;" +
        " END";

    /**
     * Update note's content when insert data with type {@link DataConstants#NOTE}
     */

    /**
     /**
     * 1.作用：维护笔记内容与数据记录的同步性
     * 2.变量名：DATA_UPDATE_NOTE_CONTENT_ON_INSERT_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当新的笔记数据记录插入时，自动更新关联笔记的摘要内容
     *      确保笔记列表中能快速显示最新的笔记内容片段
     *      仅对MIME类型为笔记的数据记录生效，避免处理其他类型数据
     */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_INSERT_TRIGGER =
        "CREATE TRIGGER update_note_content_on_insert " +
        " AFTER INSERT ON " + TABLE.DATA +
        " WHEN new." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=new." + DataColumns.CONTENT +
        "  WHERE " + NoteColumns.ID + "=new." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * Update note's content when data with {@link DataConstants#NOTE} type has changed
     */

    /**
     * 1.作用：维护笔记摘要与内容数据的实时同步
     * 2.变量名：DATA_UPDATE_NOTE_CONTENT_ON_UPDATE_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当笔记内容数据更新时，自动同步更新笔记的摘要字段
     *      确保笔记列表中显示的内容预览始终反映最新修改
     *      通过条件过滤仅处理MIME类型为笔记的数据记录
     */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER update_note_content_on_update " +
        " AFTER UPDATE ON " + TABLE.DATA +
        " WHEN old." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=new." + DataColumns.CONTENT +
        "  WHERE " + NoteColumns.ID + "=new." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * Update note's content when data with {@link DataConstants#NOTE} type has deleted
     */
    /**
     * 1.作用：维护笔记摘要与内容数据的一致性
     * 2.变量名：DATA_UPDATE_NOTE_CONTENT_ON_DELETE_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当笔记内容数据被删除时，自动清空关联笔记的摘要字段
     *      确保笔记列表中不会显示已删除的内容预览
     *      通过条件过滤仅处理MIME类型为笔记的数据记录
     */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_DELETE_TRIGGER =
        "CREATE TRIGGER update_note_content_on_delete " +
        " AFTER delete ON " + TABLE.DATA +
        " WHEN old." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=''" +
        "  WHERE " + NoteColumns.ID + "=old." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * Delete datas belong to note which has been deleted
     */
    /**
     * 1.作用：维护数据完整性，实现级联删除
     * 2.变量名：NOTE_DELETE_DATA_ON_DELETE_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当笔记主记录被删除时，自动删除该笔记关联的所有内容数据
     *      确保数据库中不会残留无主的数据记录
     *      实现逻辑上的级联删除，避免数据孤岛
     */
    private static final String NOTE_DELETE_DATA_ON_DELETE_TRIGGER =
        "CREATE TRIGGER delete_data_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN" +
        "  DELETE FROM " + TABLE.DATA +
        "   WHERE " + DataColumns.NOTE_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    /**
     * Delete notes belong to folder which has been deleted
     */
    /**
     * 1.作用：维护文件夹层级结构的完整性，实现级联删除
     * 2.变量名：FOLDER_DELETE_NOTES_ON_DELETE_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当文件夹被删除时，自动删除该文件夹下的所有子笔记
     *      确保数据库中不会残留无主的笔记记录
     *      实现树形结构中的级联删除，避免数据孤岛
     */
    private static final String FOLDER_DELETE_NOTES_ON_DELETE_TRIGGER =
        "CREATE TRIGGER folder_delete_notes_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN" +
        "  DELETE FROM " + TABLE.NOTE +
        "   WHERE " + NoteColumns.PARENT_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    /**
     * Move notes belong to folder which has been moved to trash folder
     */
    /**
     * 1.作用：维护回收站功能的完整性，实现文件夹级联移动
     * 2.变量名：FOLDER_MOVE_NOTES_ON_TRASH_TRIGGER
     * 3.类型：String
     * 4.功能：
     *      当文件夹被移入回收站时，自动将该文件夹下的所有子笔记也移入回收站
     *      确保文件夹及其内容在回收站中保持层级关系
     *      实现树形结构中的级联移动，避免子笔记遗留在原位置
     */
    private static final String FOLDER_MOVE_NOTES_ON_TRASH_TRIGGER =
        "CREATE TRIGGER folder_move_notes_on_trash " +
        " AFTER UPDATE ON " + TABLE.NOTE +
        " WHEN new." + NoteColumns.PARENT_ID + "=" + Notes.ID_TRASH_FOLER +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.PARENT_ID + "=" + Notes.ID_TRASH_FOLER +
        "  WHERE " + NoteColumns.PARENT_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    public NotesDatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    /**
     * 1.作用：创建笔记主表
     * 2.方法名：createNoteTable
     * 3.参数：
     *      SQLiteDatabase db：数据库实例
     * 4.返回类型：void
     * 5.功能：
     *      执行 SQL 语句创建笔记表结构
     *      重建相关数据库触发器
     *      初始化系统文件夹数据
     */
    public void createNoteTable(SQLiteDatabase db) {
        db.execSQL(CREATE_NOTE_TABLE_SQL);
        reCreateNoteTableTriggers(db);
        createSystemFolder(db);
        Log.d(TAG, "note table has been created");
    }

    /**
     * 1.作用：重建笔记表触发器
     * 2.方法名：reCreateNoteTableTriggers
     * 3.参数：
     *      SQLiteDatabase db：数据库实例
     * 4.返回类型：void
     * 5.功能：
     *      删除旧版触发器
     *      创建新版触发器
     *      实现文件夹计数、级联删除等功能
     */

    private void reCreateNoteTableTriggers(SQLiteDatabase db) {
        db.execSQL("DROP TRIGGER IF EXISTS increase_folder_count_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS decrease_folder_count_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS decrease_folder_count_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS delete_data_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS increase_folder_count_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS folder_delete_notes_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS folder_move_notes_on_trash");

        db.execSQL(NOTE_INCREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER);
        db.execSQL(NOTE_DECREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER);
        db.execSQL(NOTE_DECREASE_FOLDER_COUNT_ON_DELETE_TRIGGER);
        db.execSQL(NOTE_DELETE_DATA_ON_DELETE_TRIGGER);
        db.execSQL(NOTE_INCREASE_FOLDER_COUNT_ON_INSERT_TRIGGER);
        db.execSQL(FOLDER_DELETE_NOTES_ON_DELETE_TRIGGER);
        db.execSQL(FOLDER_MOVE_NOTES_ON_TRASH_TRIGGER);
    }

    /**
     * 1.作用：创建系统默认文件夹
     * 2.方法名：createSystemFolder
     * 3.参数：
     *      SQLiteDatabase db：数据库实例
     * 4.返回类型：void
     * 5.功能：
     *      创建通话记录文件夹
     *      创建根目录文件夹
     *      创建临时文件夹
     *      创建回收站文件夹
     */

    private void createSystemFolder(SQLiteDatabase db) {
        ContentValues values = new ContentValues();

        /**
         * call record foler for call notes
         */
        values.put(NoteColumns.ID, Notes.ID_CALL_RECORD_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * root folder which is default folder
         */
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_ROOT_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * temporary folder which is used for moving note
         */
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_TEMPARAY_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * create trash folder
         */
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_TRASH_FOLER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);
    }

    /**
     * 1.作用：创建系统默认文件夹
     * 2.方法名：createSystemFolder
     * 3.参数：
     *      SQLiteDatabase db：数据库实例
     * 4.返回类型：void
     */
    public void createDataTable(SQLiteDatabase db) {
        db.execSQL(CREATE_DATA_TABLE_SQL);
        reCreateDataTableTriggers(db);
        db.execSQL(CREATE_DATA_NOTE_ID_INDEX_SQL);
        Log.d(TAG, "data table has been created");
    }

    /**
     * 1.作用：重建数据表相关触发器
     * 2.方法名：reCreateDataTableTriggers
     * 3.参数：
     *      SQLiteDatabase db：数据库实例
     * 4.返回类型：void
     * 5.功能：
     *      删除旧版触发器（插入/更新/删除）
     */
    private void reCreateDataTableTriggers(SQLiteDatabase db) {
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_delete");

        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_INSERT_TRIGGER);
        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_UPDATE_TRIGGER);
        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_DELETE_TRIGGER);
    }

    /**
     * 1.作用：获取NotesDatabaseHelper的单例实例
     * 2.方法名：getInstance
     * 3.参数：
     *      Context context：应用上下文
     * 4.返回类型：NotesDatabaseHelper
     * 5.功能：
     *      确保全局只有一个数据库帮助类实例
     *      避免多实例导致的数据库连接冲突
     *      提供线程安全的实例访问方式
     */
    static synchronized NotesDatabaseHelper getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new NotesDatabaseHelper(context);
        }
        return mInstance;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        createNoteTable(db);
        createDataTable(db);
    }

    /**
     * 1.作用：执行数据库版本升级
     * 2.方法名：onUpgrade
     * 3.参数：
     *      SQLiteDatabase db：数据库实例
     *      int oldVersion：当前数据库版本
     *      int newVersion：目标数据库版本
     * 4.返回类型：void
     * 5.功能：
     *      处理跨版本升级路径
     *      执行特定版本的升级脚本
     *      在必要时重建触发器
     *      验证升级是否成功完成
     */
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        boolean reCreateTriggers = false;
        boolean skipV2 = false;

        if (oldVersion == 1) {
            upgradeToV2(db);
            skipV2 = true; // this upgrade including the upgrade from v2 to v3
            oldVersion++;
        }

        if (oldVersion == 2 && !skipV2) {
            upgradeToV3(db);
            reCreateTriggers = true;
            oldVersion++;
        }

        if (oldVersion == 3) {
            upgradeToV4(db);
            oldVersion++;
        }

        if (reCreateTriggers) {
            reCreateNoteTableTriggers(db);
            reCreateDataTableTriggers(db);
        }

        if (oldVersion != newVersion) {
            throw new IllegalStateException("Upgrade notes database to version " + newVersion
                    + "fails");
        }
    }

    /**
     * 1.作用：将数据库升级到版本2
     * 2.方法名：upgradeToV2
     * 3.参数：
     *      SQLiteDatabase db：数据库实例
     * 4.返回类型：void
     * 5.功能：
     *      删除旧版笔记表和数据表
     *      重新创建新版笔记表和数据表
     *      实现版本1到版本2的结构转换
     */
    private void upgradeToV2(SQLiteDatabase db) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE.NOTE);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE.DATA);
        createNoteTable(db);
        createDataTable(db);
    }

    /**
     * 1.作用：将数据库升级到版本3
     * 2.方法名：upgradeToV3
     * 3.参数：
     *      SQLiteDatabase db：数据库实例
     * 4.返回类型：void
     * 5.功能：
     *      删除不再使用的触发器
     *      添加Gtask ID字段用于Google任务同步
     *      创建回收站系统文件夹
     *      为版本3新增功能做准备
     *
     */
    private void upgradeToV3(SQLiteDatabase db) {
        // drop unused triggers
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_update");
        // add a column for gtask id
        db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.GTASK_ID
                + " TEXT NOT NULL DEFAULT ''");
        // add a trash system folder
        ContentValues values = new ContentValues();
        values.put(NoteColumns.ID, Notes.ID_TRASH_FOLER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);
    }

    private void upgradeToV4(SQLiteDatabase db) {
        db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.VERSION
                + " INTEGER NOT NULL DEFAULT 0");
    }
}