《Android》：6.数据存储_3_SQLite存储之升级数据库

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6.4.2 升级数据库

使用MyDatabaseHelper中的onUpgrade()方法，对数据库进行升级操作

要实现的内容：
在DatabaseTest项目（上一篇内容）中已经有一张Book表，现在再添加一张表进数据库

修改上节中MyDatabaseHelper类如下：

package com.zyf.android.databasetest;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.Toast;

public class MyDatabaseHelper extends SQLiteOpenHelper {

    //创建表sql语句
    public static final String CREATE_BOOK = "create table Book("
            + "id integer primary key autoincrement,"
            + "author text,"
            + "price real,"
            + "pages integer,"
            + "name text)";

    public static final String CREATE_CATEGOTY = "create table Category("
            + "id integer primary key autoincrement,"
            + "category_name text,"
            + "category_code integer)";

    private Context mContext;

    public MyDatabaseHelper(Context context,String name,SQLiteDatabase.CursorFactory factory,
                            int version){
        super(context,name,factory,version);
        mContext =context;
    }
    //抽象方法
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_BOOK);
        db.execSQL(CREATE_CATEGOTY);//创建数据库表
        Toast.makeText(mContext,"create succeeded", Toast.LENGTH_SHORT).show();
    }

    //抽象方法（升级方法）
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists Book");//如果已经存在的Book表，就删掉重新创建
        db.execSQL("drop table if exists Category");
        onCreate(db);
    }
}

Snip20180529_5.png

修改MainActivity类如下；

package com.zyf.android.databasetest;

import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    private MyDatabaseHelper dbHelper;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbHelper = new MyDatabaseHelper(this,"BookStore.db",null,3);
        Button createDatabase = (Button) findViewById(R.id.create_database);
        createDatabase.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dbHelper.getWritableDatabase();
            }
        });
   }
}

Snip20180529_6.png

运行代码，点击按钮，用adb 和sqlite3 查看数据库中的表

Snip20180529_2.png

写在最后
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