王希宁 2023317170

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;


public class NotesDatabaseHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "note.db";  // 数据库名称

    private static final int DB_VERSION = 4;  // 数据库版本号

    public interface TABLE {
        public static final String NOTE = "note";  // 笔记表名称

        public static final String DATA = "data";  // 数据表名称
    }

    private static final String TAG = "NotesDatabaseHelper";  // 日志标签

    private static NotesDatabaseHelper mInstance;  // 单例实例

    private static final String CREATE_NOTE_TABLE_SQL =  // 创建笔记表的SQL语句
        "CREATE TABLE " + TABLE.NOTE + "(" +
            NoteColumns.ID + " INTEGER PRIMARY KEY," +
            // ... 省略其他字段
            NoteColumns.VERSION + " INTEGER NOT NULL DEFAULT 0" +
        ")";

    private static final String CREATE_DATA_TABLE_SQL =  // 创建数据表的SQL语句
        "CREATE TABLE " + TABLE.DATA + "(" +
            DataColumns.ID + " INTEGER PRIMARY KEY," +
            // ... 省略其他字段
            DataColumns.DATA5 + " TEXT NOT NULL DEFAULT ''" +
        ")";

    private static final String CREATE_DATA_NOTE_ID_INDEX_SQL =  // 创建数据表的索引SQL语句
        "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
     */
    private static final String NOTE_INCREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER =  // 创建触发器的SQL语句
        "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";

    /** 
     * 其他代码...
     */
}
```

这里对数据库帮助类的各个部分进行了注释说明，包括数据库名称、版本号、表名称、创建表的SQL语句等。希望这样的注释能够帮助你更好地理解和使用这段代码。
```java
    /**
     * 当将笔记从文件夹中移出时，减少文件夹中的笔记数量
     */
    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";

    /**
     * 将新笔记插入到文件夹中时，增加文件夹中的笔记数量
     */
    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";

    /**
     * 当从文件夹中删除笔记时，减少文件夹中的笔记数量
     */
    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";

    /**
     * 当插入类型为{@link DataConstants#NOTE}的数据时，更新笔记内容
     */
    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";

    /**
     * 当类型为{@link DataConstants#NOTE}的数据发生更改时，更新
```java
/**
 * 当数据类型为{@link DataConstants#NOTE}的数据被删除时，更新笔记内容
 */
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";

/**
 * 删除已删除笔记所属的数据
 */
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";

/**
 * 删除已删除文件夹所属的笔记
 */
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";

/**
 * 将已移至回收站文件夹的文件夹中的笔记移至回收站
 */
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);
}

public void createNoteTable(SQLiteDatabase db) {
    db.execSQL(CREATE_NOTE_TABLE_SQL);
    reCreateNoteTableTriggers(db);
    createSystemFolder(db);
    Log.d(TAG, "note table has been created");
}
```
```java
/**
 * 重新创建笔记表的触发器
 * @param db SQLiteDatabase对象
 */
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);
}

/**
 * 创建系统文件夹
 * @param db SQLiteDatabase对象
 */
private void createSystemFolder(SQLiteDatabase db) {
    ContentValues values = new ContentValues();

    /**
     * 通话记录文件夹
     */
    values.put(NoteColumns.ID, Notes.ID_CALL_RECORD_FOLDER);
    values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
    db.insert(TABLE.NOTE, null, values);

    /**
     * 根文件夹，即默认文件夹
     */
    values.clear();
    values.put(NoteColumns.ID, Notes.ID_ROOT_FOLDER);
    values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
    db.insert(TABLE.NOTE, null, values);

    /**
     * 临时文件夹，用于移动笔记
     */
    values.clear();
    values.put(NoteColumns.ID, Notes.ID_TEMPARAY_FOLDER);
    values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
    db.insert(TABLE.NOTE, null, values);

    /**
     * 创建回收站文件夹
     */
    values.clear();
    values.put(NoteColumns.ID, Notes.ID_TRASH_FOLER);
    values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
    db.insert(TABLE.NOTE, null, values);
}

/**
 * 创建数据表
 * @param db SQLiteDatabase对象
 */
public void createDataTable(SQLiteDatabase db) {
    db.execSQL(CREATE_DATA_TABLE_SQL);
    reCreateDataTableTriggers(db);
    db.execSQL(CREATE_DATA_NOTE_ID_INDEX_SQL);
    Log.d(TAG, "数据表已创建");
}

/**
 * 重新创建数据表的触发器
 * @param db SQLiteDatabase对象
 */
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);
}

/**
 * 获取NotesDatabaseHelper的实例
 * @param context 上下文对象
 * @return NotesDatabaseHelper的实例
 */
static synchronized NotesDatabaseHelper getInstance(Context
```java
/**
 * 数据库升级方法
 * @param db SQLiteDatabase对象
 * @param oldVersion 旧版本号
 * @param newVersion 新版本号
 */
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    boolean reCreateTriggers = false;
    boolean skipV2 = false;

    if (oldVersion == 1) {
        upgradeToV2(db);
        skipV2 = true; // 此升级包括从v2到v3的升级
        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("升级笔记数据库到版本 " + newVersion
                + " 失败");
    }
}

/**
 * 升级到版本2的方法
 * @param db SQLiteDatabase对象
 */
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);
}

/**
 * 升级到版本3的方法
 * @param db SQLiteDatabase对象
 */
private void upgradeToV3(SQLiteDatabase db) {
    // 删除未使用的触发器
    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");
    // 添加一个用于gtask id的列
    db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.GTASK_ID
            + " TEXT NOT NULL DEFAULT ''");
    // 添加一个垃圾箱系统文件夹
    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);
}

/**
 * 升级到版本4的方法
 * @param db SQLiteDatabase对象
 */
private void upgradeToV4(SQLiteDatabase db) {
    db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.VERSION
            + " INTEGER NOT NULL DEFAULT 0");
}
```