Android-事務(Transaction)

事務就拿轉帳的例子來說：兩個用戶，要么都成功，要么都失敗，這樣才是安全🔐的，可以保證兩方或者多方，全部成功才成功，否則就回滾（不會對數據有任何修改）

 

定義數據庫與表

package liudeli.datastorage.db;

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

public class MySQLiteOpenHelper2 extends SQLiteOpenHelper {

    public static MySQLiteOpenHelper2 mySQLiteOpenHelper;

    /**
     * 由於表名每次使用很頻繁，所有定義成常量
     */
    public static final String TABLE_NAME = "person_table";

    private static final String DB_NAME = "csbank.db";
    private static final int VERSION = 1;

    public synchronized static MySQLiteOpenHelper2 getInstance(Context context) {
        if (null == mySQLiteOpenHelper) {
            mySQLiteOpenHelper = new MySQLiteOpenHelper2(context, DB_NAME, null, VERSION);
        }
        return mySQLiteOpenHelper;
    }

    /**
     * 當開發者調用 getReadableDatabase(); 或者 getWritableDatabase();
     * 就會通過此構造方法配置的信息 來創建 person_info.db 數據庫
     * 此方法的另外作用是，如果存着數據庫就打開數據庫，不存着數據庫就創建數據庫
     * @param context 上下文
     * @param name    數據庫名
     * @param factory 游標工廠
     * @param version 版本，最低為1
     */
    private MySQLiteOpenHelper2(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    /**
     * 此方法是何時調用? ，是需要開發者調用 getReadableDatabase(); 或者 getWritableDatabase();
     * 此方法的作用是，如果沒有表就創建打開，如果有表就打開
     * @param db 可執行SQL語句
     */
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table "+TABLE_NAME+"(_id integer primary key autoincrement, name text, age integer, my_assets text);");

        ContentValues values = new ContentValues();
        values.put("name", "張三");
        values.put("age", 62);
        values.put("my_assets", "1000000");
        db.insert(TABLE_NAME, null, values);

        values.put("name", "李四");
        values.put("age", 22);
        values.put("my_assets", "2000");
        db.insert(TABLE_NAME, null, values);
    }

    /**
     * 此方法用於數據庫升級
     * @param db 可執行SQL語句
     * @param oldVersion 以前舊版本的版本號
     * @param newVersion 現在目前最新的版本號
     */
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

 

事務的實際操作：

package liudeli.datastorage;

import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

import liudeli.datastorage.db.MySQLiteOpenHelper2;

public class TransactionActivity extends Activity {

    private final String TAG = TransactionActivity.class.getSimpleName();

    MySQLiteOpenHelper2 dbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_transaction);

        dbHelper = MySQLiteOpenHelper2.getInstance(this);
    }

    public void queryALl(View view) {
        query(null); // 查詢全部
    }

    private void query(String orderBy) {
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        Cursor cursor = db.query(MySQLiteOpenHelper2.TABLE_NAME,
                new String[]{"*"},
                null,
                null,
                null,
                null,
                orderBy);
        while (cursor.moveToNext()) {
            int _id = cursor.getInt(0);
            String name = cursor.getString(1);
            int age = cursor.getInt(2);
            String myAssets = cursor.getString(3);
            Log.d(TAG, " id:" + _id + " name:" + name + " age" + age + " my_assets:" + myAssets);
        }
        cursor.close();
        db.close();
    }

    /**
     * 轉賬
     * @param view
     */
    public void moveMoney(View view) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        try {
            int moneyValue1 = 1000000;
            int moneyValue2 = 2000;

            db.beginTransaction(); // 開啟事務

            ContentValues contentValues = new ContentValues();
            contentValues.put("my_assets", moneyValue1 - 6000);
            int result1 = db.update(MySQLiteOpenHelper2.TABLE_NAME, contentValues, "_id = ?", new String[]{"1"});

            contentValues.put("my_assets", moneyValue2 + 6000);
            int result2 = db.update(MySQLiteOpenHelper2.TABLE_NAME, contentValues, "_id = ?", new String[]{"2"});

            if (result1>0 && result2>0) {
                db.setTransactionSuccessful(); // 事務默認是失敗的，要設置成功，否則數據不會修改
                Toast.makeText(TransactionActivity.this, "轉帳成功", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(TransactionActivity.this, "轉帳失敗", Toast.LENGTH_SHORT).show();
            }
        } catch (Exception e) {
            e.printStackTrace();
            Toast.makeText(TransactionActivity.this, "轉帳失敗", Toast.LENGTH_SHORT).show();

        } finally {

            db.endTransaction(); // 注意⚠️：一定要結束事務，不然查詢會報錯

            db.close();
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
    }
}

 

Layout：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="轉賬"
        android:onClick="moveMoney"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="queryALl"
        android:text="查詢"
        android:layout_alignParentRight="true"
        />

</RelativeLayout>