如何将一个长而单一的SQLiteOpenHelper分成几个类，每个表一个

Question

如何将一个长而单一的SQLiteOpenHelper分成几个类，每个表一个

edd*_*ddy 2 sqlite android sqliteopenhelper android-sqlite

我知道这已经被问过几次了，但是在所有这些问题中，OP和回答者都没有提供清晰的例子。

所以我想问的是是否有这样的课程

public class MyDatabaseDB {

    // database constants
    public static final String DB_NAME = "mydatabase.db";
    public static final int    DB_VERSION = 1;

    // list table constants
    public static final String LIST_TABLE = "list";

    public static final String LIST_ID = "_id";
    public static final int    LIST_ID_COL = 0;

    public static final String LIST_NAME = "list_name";
    public static final int    LIST_NAME_COL = 1;

    // task table constants
    public static final String TASK_TABLE = "task";

    public static final String TASK_ID = "_id";
    public static final int    TASK_ID_COL = 0;

    public static final String TASK_LIST_ID = "list_id";
    public static final int    TASK_LIST_ID_COL = 1;

    public static final String TASK_NAME = "task_name";
    public static final int    TASK_NAME_COL = 2; 

    // CREATE and DROP TABLE statements
    public static final String CREATE_LIST_TABLE = 
            "CREATE TABLE " + LIST_TABLE + " (" + 
            LIST_ID   + " INTEGER PRIMARY KEY AUTOINCREMENT, " + 
            LIST_NAME + " TEXT    UNIQUE)";

    public static final String CREATE_TASK_TABLE = 
            "CREATE TABLE " + TASK_TABLE + " (" + 
            TASK_ID         + " INTEGER PRIMARY KEY AUTOINCREMENT, " + 
            TASK_LIST_ID    + " INTEGER, " + 
            TASK_NAME       + " TEXT " + 
           )";

    public static final String DROP_LIST_TABLE = 
            "DROP TABLE IF EXISTS " + LIST_TABLE;

    public static final String DROP_TASK_TABLE = 
            "DROP TABLE IF EXISTS " + TASK_TABLE;

    private static class DBHelper extends SQLiteOpenHelper {

        public DBHelper(Context context, String name, 
                CursorFactory factory, int version) {
            super(context, name, factory, version);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            // create tables
            db.execSQL(CREATE_LIST_TABLE);
            db.execSQL(CREATE_TASK_TABLE);

            // insert lists
            db.execSQL("INSERT INTO list VALUES (1, 'Hobbies')");
            db.execSQL("INSERT INTO list VALUES (2, 'Sports')");

            // insert sample tasks
            db.execSQL("INSERT INTO task VALUES (1, 1, 'Play the guitar')");
            db.execSQL("INSERT INTO task VALUES (2, 1, 'Play video games')");
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, 
                int oldVersion, int newVersion) {

            Log.d("Task list", "Upgrading db from version " 
                    + oldVersion + " to " + newVersion);


            db.execSQL(MyDatabaseDB.DROP_LIST_TABLE);
            db.execSQL(MyDatabaseDB.DROP_TASK_TABLE);
            onCreate(db);
        }
    }

    // database object and database helper object
    private SQLiteDatabase db;
    private DBHelper dbHelper;

    // constructor
    public MyDatabaseDB(Context context) {
        dbHelper = new DBHelper(context, DB_NAME, null, DB_VERSION);
    }

    // private methods
    private void openReadableDB() {
        db = dbHelper.getReadableDatabase();
    }

    private void openWriteableDB() {
        db = dbHelper.getWritableDatabase();
    }

    private void closeDB() {
        if (db != null)
            db.close();
    }

    // public methods   

    public long insertTask(Task task) {
        ContentValues cv = new ContentValues();
        cv.put(TASK_LIST_ID, task.getListId());
        cv.put(TASK_NAME, task.getName());        

        this.openWriteableDB();
        long rowID = db.insert(TASK_TABLE, null, cv);
        this.closeDB();

        return rowID;
    }    

    public int updateTask(Task task) {
        ContentValues cv = new ContentValues();
        cv.put(TASK_LIST_ID, task.getListId());
        cv.put(TASK_NAME, task.getName());        

        String where = TASK_ID + "= ?";
        String[] whereArgs = { String.valueOf(task.getId()) };

        this.openWriteableDB();
        int rowCount = db.update(TASK_TABLE, cv, where, whereArgs);
        this.closeDB();

        return rowCount;
    }    

    public int deleteTask(long id) {
        String where = TASK_ID + "= ?";
        String[] whereArgs = { String.valueOf(id) };

        this.openWriteableDB();
        int rowCount = db.delete(TASK_TABLE, where, whereArgs);
        this.closeDB();

        return rowCount;
    }
}

Run Code Online (Sandbox Code Playgroud)

这是我的课程的简化版本，使用我在网上找到的一些代码构建。在此示例中，我仅显示两个表的代码：List和Task，以及仅一些Task表的sql方法：insertTask，updateTask和deleteTask。

即使上面显示的代码有效，但我想让所有的代码都位于同一个类中，而不是让十个表都很好。因此，我尝试将所有这些代码分成几个类，每个表一个。像这样：

public class MyDatabaseDB {

    // database constants
    public static final String DB_NAME = "mydatabase.db";
    public static final int    DB_VERSION = 1;


    private static class DBHelper extends SQLiteOpenHelper {

        public DBHelper(Context context, String name, 
                CursorFactory factory, int version) {
            super(context, name, factory, version);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            // create tables
            db.execSQL(ListDAL.CREATE_LIST_TABLE);
            db.execSQL(TaskDAL.CREATE_TASK_TABLE);

            // insert lists
            db.execSQL("INSERT INTO list VALUES (1, 'Hobbies')");
            db.execSQL("INSERT INTO list VALUES (2, 'Sports')");

            // insert sample tasks
            db.execSQL("INSERT INTO task VALUES (1, 1, 'Play the guitar')");
            db.execSQL("INSERT INTO task VALUES (2, 1, 'Play video games')");
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, 
                int oldVersion, int newVersion) {

            Log.d("Task list", "Upgrading db from version " 
                    + oldVersion + " to " + newVersion);


            db.execSQL(ListDAL.DROP_LIST_TABLE);
            db.execSQL(TaskDAL.DROP_TASK_TABLE);
            onCreate(db);
        }
    }

    // database object and database helper object
    private SQLiteDatabase db;
    private DBHelper dbHelper;

    // constructor
    public MyDatabaseDB(Context context) {
        dbHelper = new DBHelper(context, DB_NAME, null, DB_VERSION);
    }

    // private methods
    private void openReadableDB() {
        db = dbHelper.getReadableDatabase();
    }

    private void openWriteableDB() {
        db = dbHelper.getWritableDatabase();
    }

    private void closeDB() {
        if (db != null)
            db.close();
    }   

}

Run Code Online (Sandbox Code Playgroud)

这是两个新类，我创建了与特定表相关的代码：

ListDAL没有太多代码

public class ListDAL {

   // list table constants
    public static final String LIST_TABLE = "list";

    public static final String LIST_ID = "_id";
    public static final int    LIST_ID_COL = 0;

    public static final String LIST_NAME = "list_name";
    public static final int    LIST_NAME_COL = 1;

    // CREATE and DROP TABLE statements
    public static final String CREATE_LIST_TABLE = 
            "CREATE TABLE " + LIST_TABLE + " (" + 
            LIST_ID   + " INTEGER PRIMARY KEY AUTOINCREMENT, " + 
            LIST_NAME + " TEXT    UNIQUE)";

    public static final String DROP_LIST_TABLE = 
            "DROP TABLE IF EXISTS " + LIST_TABLE;


}

Run Code Online (Sandbox Code Playgroud)

该TaskDAL类是包含大部分代码的之一，它是在这个类中，我有问题，特别是在insertTask，updateTask和DeleteTask活动与像调用 this.openWriteableDB（），this.openWriteableDB（）或类似的呼叫 分贝.insert（TASK_TABLE，null，cv）。

由于这些方法不再位于TaskDAL中，因此无法访问它们。我尝试传递一些对这些方法的引用以代替this或db，但是它没有用

public class TaskDAL {
    // task table constants
    public static final String TASK_TABLE = "task";

    public static final String TASK_ID = "_id";
    public static final int    TASK_ID_COL = 0;

    public static final String TASK_LIST_ID = "list_id";
    public static final int    TASK_LIST_ID_COL = 1;

    public static final String TASK_NAME = "task_name";
    public static final int    TASK_NAME_COL = 2; 

    // CREATE and DROP TABLE statements
    public static final String CREATE_TASK_TABLE = 
            "CREATE TABLE " + TASK_TABLE + " (" + 
            TASK_ID         + " INTEGER PRIMARY KEY AUTOINCREMENT, " + 
            TASK_LIST_ID    + " INTEGER, " + 
            TASK_NAME       + " TEXT " + 
           )";
    public static final String DROP_TASK_TABLE = 
            "DROP TABLE IF EXISTS " + TASK_TABLE;       

     // public methods   

    public long insertTask(Task task) {
        ContentValues cv = new ContentValues();
        cv.put(TASK_LIST_ID, task.getListId());
        cv.put(TASK_NAME, task.getName());        

        this.openWriteableDB();
        long rowID = db.insert(TASK_TABLE, null, cv);
        this.closeDB();

        return rowID;
    }    

    public int updateTask(Task task) {
        ContentValues cv = new ContentValues();
        cv.put(TASK_LIST_ID, task.getListId());
        cv.put(TASK_NAME, task.getName());        

        String where = TASK_ID + "= ?";
        String[] whereArgs = { String.valueOf(task.getId()) };

        this.openWriteableDB();
        int rowCount = db.update(TASK_TABLE, cv, where, whereArgs);
        this.closeDB();

        return rowCount;
    }    

    public int deleteTask(long id) {
        String where = TASK_ID + "= ?";
        String[] whereArgs = { String.valueOf(id) };

        this.openWriteableDB();
        int rowCount = db.delete(TASK_TABLE, where, whereArgs);
        this.closeDB();

        return rowCount;
    }
}

Run Code Online (Sandbox Code Playgroud)

那么，你们中有没有人尝试过类似的事情？如果我设法将数据库代码正确地分成几个类，我仍然可以联接表吗？

附言：请不要关闭此问题，如果您认为我做错了什么，请告诉我，我会尽力予以纠正

Answer 1

Com*_*are 5

你认为你可以给一些提示如何做吗

这与Android无关，甚至与Java无关。将长的编程结构（例如Java中的类）分解为较小的结构具有标准技术，称为设计模式，具有特定于语言的实现。

例如，您可以使用复合模式：

定义一个接口-我TableHelper在这里称其为-具有onCreate()和接口onUpdate()匹配的接口SQLiteOpenHelper
定义N个类（每个表一个），该类实现该TableHelper接口并提供该表的创建和升级逻辑（以及您想要在这些类上拥有的任何其他业务逻辑）
有你SQLiteOpenHelper定义TableHelper[]你的含实例TableHelper类，并将其委托onCreate()以及onUpgrade()那些TableHelper通过遍历数组切换实例

归档时间：	11 年，5 月前
查看次数：	980 次
最近记录：	9 年前