MiNotes/doc/成员代码分析/jhw/NotesDatabaseHelper.java

//数据库操作，SQLOpenhelper,对一些note和文件进行数据库的操作。比如删除文件后，将文件里的note也相应删除
package net.micode.notes.data;
//保存一些数据信息，这些数据可以被数据库操作

import android.content.ContentValues;
//加载和访问资源
import android.content.Context;
//主要提供了对应于添加、删除、更新、查询的操作
import android.database.sqlite.SQLiteDatabase;
//数据库的更新和创建
import android.database.sqlite.SQLiteOpenHelper;
//安卓日志类接口
import android.util.Log;
//导入Notes.java中的DataColumns, NoteColumns接口，和类DataConstants
import net.micode.notes.data.Notes.DataColumns;
import net.micode.notes.data.Notes.DataConstants;
import net.micode.notes.data.Notes.NoteColumns;

//继承于SQLiteOpenHelper的类NotesDatabaseHelper，用于实现对便签或者 文件的数据库操作，例如删除便签
public class NotesDatabaseHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "note.db";

    private static final int DB_VERSION = 4;

    public interface TABLE {
        //接口，分成note和data，在后面的程序里分别使用过
        public static final String NOTE = "note";

        public static final String DATA = "data";
    }

    //创建一个表格用来储存标签编号
    private static final String TAG = "NotesDatabaseHelper";
    //实例化一个NoteDatabaseHelper
    private static NotesDatabaseHelper mInstance;
    /**
     * 当创建一个新的便签，就产生了各类关于便签的信息，
     * 比如ID，父便签ID，背景颜色，创建日期等，
     * 我们需要把这些信息放入数据库，这就是数据库的表头。
     * 我们在下面定义的涉及操作的字符串，
     * 全都是为了在之后执行db.execSQL("字符串")。
     */
    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" + ")";

    //大体同上，这里储存的是便签内容的信息，
// 用这些信息作为数据库对便签内容存储的表头
    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 ''" + ")";
    //创建索引，名称为note_id_index，在TABLE.DATA表格的DataCloumns.NOTE_ID列
    private static final String CREATE_DATA_NOTE_ID_INDEX_SQL = "CREATE INDEX IF NOT EXISTS note_id_index ON " + TABLE.DATA + "(" + DataColumns.NOTE_ID + ");";//存储便签编号的一个数据表格

    /**
     * Increase folder's note count when move note to the folder
     * 增加文件夹便签数量，当移动一个便签进入该文件夹后，
     * 之后在db.execSQL(字符串)中用到，
     * 启动自定义的数据库update触发器，有相关的一系列数据库操作。
     */
    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
     * 同上，从文件夹移除便签，文件夹便签数量减1，
     * 以后在db.execSQL(字符串)中用到，
     * 启动自定义的数据库updata触发器，附带相关的一系列操作
     */
    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
     * 文件夹中创建新便签，文件夹便签数量+1，
     * 启动自定义的数据库insert触发器，附带相关的一系列操作
     */
    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
     * 在文件夹中删除note时，更新文件夹的note数量
     */
    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}
     * 当Note插入新的数据时，更新note的内容，并更改表格
     */
    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
     * 构建一条SQL语句，用于实现在note中改变data后，进行当前状态的更新
     */
    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
     * 当note的内容被删除时，更新表格
     */
    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
     * 删除数据库中的数据，当便签中的数据被删除时删除相应数据库
     */
    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
     * 删除属于已删除的文件夹中的便签的数据
     */
    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
     * 还原垃圾桶中便签后需要更改的数据的表格。
     */
    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);
    }
    //构造函数，传入数据库的名称和版本

    public void createNoteTable(SQLiteDatabase db) {
        db.execSQL(CREATE_NOTE_TABLE_SQL);
        reCreateNoteTableTriggers(db);
        createSystemFolder(db);
        Log.d(TAG, "note table has been created");
    }
    //创建表格（用来存储标签属性）

    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);
    }
    //execSQL是数据库操作的API，主要是更改行为的SQL语句。
    //在这里主要是用来重新创建上述定义的表格用的，先删除原来有的数据库的触发器再重新创建新的数据库

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

        /**
         * call record foler for call notes
         * 初始化ContenValues实例，然后存入相应的通话记录文件夹类型形成映射，
         */
        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
         * 对根文件夹修改，先将values实例的内容清空，然后存入values，再插入对象
         */
        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
         * 设置临时文件夹作为文件夹移动的有效目标
         */
        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
         * 创建垃圾文件夹
         */
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_TRASH_FOLER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);
    }
    //创建几个系统文件夹

    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");
    }//创建表格（用来存储标签内容）

    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);
    }//创建用于表格初始化，删除触发器，然后更新触发器

    static synchronized NotesDatabaseHelper getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new NotesDatabaseHelper(context);
        }
        return mInstance;
    }
    //上网查是为解决同一时刻只能有一个线程执行.
    //在写程序库代码时，有时有一个类需要被所有的其它类使用，
    //但又要求这个类只能被实例化一次，是个服务类，定义一次，其它类使用同一个这个类的实例

    @Override
    public void onCreate(SQLiteDatabase db) {
        createNoteTable(db);
        createDataTable(db);
    }//实现两个表格（上面创建的两个表格）

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        //是否重建的信号
        boolean reCreateTriggers = false;
        //是否从V2升级到V3
        boolean skipV2 = false;
        //判断旧版本是不是V1，如果是就升级版本到V2
        if (oldVersion == 1) {
            upgradeToV2(db);
            skipV2 = true; // this upgrade including the upgrade from v2 to v3
            oldVersion++;
        }
        //判断旧版本是V2，且未跳过V2版本，就升级版本到V3
        if (oldVersion == 2 && !skipV2) {
            upgradeToV3(db);
            reCreateTriggers = true;
            oldVersion++;
        }
        //如果旧版本是V3，就升级版本到V4
        if (oldVersion == 3) {
            upgradeToV4(db);
            oldVersion++;
        }
       //若重构触发器的值为真，那么，
        // 要把便签（note）和数据（data）表单的数据库触发器重构，调用以上的定义
        if (reCreateTriggers) {
            reCreateNoteTableTriggers(db);
            reCreateDataTableTriggers(db);
        }
        //旧版本与最新版本不一致，抛出异常
        if (oldVersion != newVersion) {
            throw new IllegalStateException("Upgrade notes database to version " + newVersion + "fails");
        }
    }
    //数据库版本的更新（数据库内容的更改）

    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);
    }
    //更新到V2版本,删除note和data表，然后新建表

    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);
    }
    //更新到V3版本，删除触发器，新增gtask和trash行，然后在表中增添表头

    private void upgradeToV4(SQLiteDatabase db) {
        db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.VERSION + " INTEGER NOT NULL DEFAULT 0");
    }//更新到V4版本,但是不知道V2、V3、V4是什么意思
}