处理多个表的最佳实践 [英] Best practices for working with multiple tables

问题描述

我在应用程序中使用具有多个表的数据库.我有一个XML解析器，需要在解析时将数据写入两个表.我为两个表都创建了两个数据库适配器，但是现在我遇到了问题.当我使用一张桌子时，很简单:

I use a database with multiple tables in my application. I have an XML parser which needs to write data to two tables while parsing. I created two database adapters for both tables, but now I have a problem. When I'm working with one table, it's easy:

FirstDBAdapter firstTable = new FirstDBAdapter(mycontext);
firstTable.open(); // open and close it every time I need to insert something
                   // may be hundreds of times while parsing
                   // it opens not a table but whole DB     
firstTable.insertItem(Item);        
firstTable.close(); 

由于它是SAX解析器，所以我认为(也许我错了)，这样会更好:

Since it's a SAX parser, in my opinion (maybe I'm wrong), this will be even better:

FirstDBAdapter firstTable = new FirstDBAdapter(mycontext);

@Override
public void startDocument() throws SAXException 
{
    firstTable.open(); // open and close only once
}

...
firstTable.insertItem(Item);
...

@Override
public void endDocument() throws SAXException 
{
    firstTable.close();
}

但是如果我需要将数据插入第二张表该怎么办?例如，如果我有第二个适配器，我认为这是个坏主意:

But how do I do it if I need to insert data to the second table? For example, if I have the second adapter, which I think will be a bad idea:

FirstDBAdapter firstTable = new FirstDBAdapter(mycontext);
SecondDBAdapter secondTable = new SecondDBAdapter(mycontext);

@Override
public void startDocument() throws SAXException 
{
    firstTable.open();
    secondTable.open(); 
}

关于如何实现这一目标的任何想法?

Any thoughts on how to achieve this?

推荐答案

我的数据库适配器.实例始终存储在从Application继承的MyApplication中.考虑一下我定义了第一个表的第二个表...目前，这只是一个简短的版本，实际上，该适配器处理数据库中的7个表.

My database adapter. An instance is always stored in MyApplication which inherites from Application. Just think about a second table where I defined the first one... currently this is just a short version, in reality this adapter handles 7 tables in the database.

public class MyDbAdapter {
    private static final String LOG_TAG = MyDbAdapter.class.getSimpleName();

    private SQLiteDatabase mDb;
    private static MyDatabaseManager mDbManager;

    public MyDbAdapter() {
        mDbManager = new MyDatabaseManager(MyApplication.getApplication());
        mDb = mDbManager.getWritableDatabase();
    }

    public static final class GameColumns implements BaseColumns {
        public static final String TABLE = "game";
        public static final String IMEI = "imei";
        public static final String LAST_UPDATE = "lastupdate";
        public static final String NICKNAME = "nickname";
    }

    public String getImei() {
        checkDbState();
        String retValue = "";
        Cursor c = mDb.rawQuery("SELECT imei FROM " + GameColumns.TABLE, null);
        if (c.moveToFirst()) {
            retValue = c.getString(c.getColumnIndex(GameColumns.IMEI));
        }
        c.close();
        return retValue;
    }

    public void setImei(String imei) {
        checkDbState();
        ContentValues cv = new ContentValues();
        cv.put(GameColumns.IMEI, imei);
        mDb.update(GameColumns.TABLE, cv, null, null);
    }

    public boolean isOpen() {
        return mDb != null && mDb.isOpen();
    }

    public void open() {
        mDbManager = new MyDatabaseManager(MyApplication.getApplication());
        if (!isOpen()) {
            mDb = mDbManager.getWritableDatabase();
        }
    }

    public void close() {
        if (isOpen()) {
            mDb.close();
            mDb = null;
            if (mDbManager != null) {
                mDbManager.close();
                mDbManager = null;
            }
        }
    }

    private void checkDbState() {
        if (mDb == null || !mDb.isOpen()) {
            throw new IllegalStateException("The database has not been opened");
        }
    }

    private static class MyDatabaseManager extends SQLiteOpenHelper {
        private static final String DATABASE_NAME = "dbname";
        private static final int DATABASE_VERSION = 7;

        private MyDatabaseManager(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

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

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            Log.w(LOG_TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + "!");
        }

        private void dropDatabase(SQLiteDatabase db) {
            db.execSQL("DROP TABLE IF EXISTS " + GameColumns.TABLE);
        }

        private void createGameTable(SQLiteDatabase db) {
            db.execSQL("CREATE TABLE " + GameColumns.TABLE + " ("
                    + GameColumns._ID + " INTEGER PRIMARY KEY,"
                    + GameColumns.IMEI + " TEXT,"
                    + GameColumns.LAST_UPDATE + " TEXT,"
                    + GameColumns.NICKNAME + " TEXT);");
            ContentValues cv = new ContentValues();
            cv.put(GameColumns.IMEI, "123456789012345");
            cv.put(GameColumns.LAST_UPDATE, 0);
            cv.put(GameColumns.NICKNAME, (String) null);
            db.insert(GameColumns.TABLE, null, cv);
        }
    }
}

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