数据库的初始化和升级（代码）

Posted 2020-07-22 安然罒

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3     xmlns:tools="http://schemas.android.com/tools"
 4     android:layout_width="match_parent"
 5     android:layout_height="match_parent"
 6     android:paddingBottom="@dimen/activity_vertical_margin"
 7     android:paddingLeft="@dimen/activity_horizontal_margin"
 8     android:paddingRight="@dimen/activity_horizontal_margin"
 9     android:paddingTop="@dimen/activity_vertical_margin"
10     tools:context="com.hanqi.testapp3.TestActivity2"
11     android:orientation="vertical">
12 
13     <Button
14         android:layout_width="match_parent"
15         android:layout_height="wrap_content"
16         android:text="初始化数据库"
17         android:onClick="bt1_OnClick"/>
18 
19     <Button
20         android:layout_width="match_parent"
21         android:layout_height="wrap_content"
22         android:text="升级数据库"
23         android:onClick="bt2_OnClick"/>
24 
25 
26 </LinearLayout>

.xml

  1 package com.hanqi.testapp3;
  2 
  3 import android.content.ContentValues;
  4 import android.database.Cursor;
  5 import android.database.sqlite.SQLiteDatabase;
  6 import android.database.sqlite.SQLiteOpenHelper;
  7 import android.support.v7.app.AppCompatActivity;
  8 import android.os.Bundle;
  9 import android.util.Log;
 10 import android.view.View;
 11 import android.widget.EditText;
 12 import android.widget.Toast;
 13 
 14 public class TestActivity2 extends AppCompatActivity {
 15 
 16 
 17     @Override
 18     protected void onCreate(Bundle savedInstanceState) {
 19         super.onCreate(savedInstanceState);
 20         setContentView(R.layout.activity_test2);
 21 
 22     }
 23 
 24     //初始化数据库
 25     public void bt1_OnClick(View v)
 26     {
 27         //使用工具类得到数据库对象
 28         MyDBHelper myDBHelper=new MyDBHelper("test.db",2);
 29 
 30         //得到连接
 31         SQLiteDatabase sd=myDBHelper.getReadableDatabase();
 32 
 33         Toast.makeText(TestActivity2.this, "连接数据库成功", Toast.LENGTH_SHORT).show();
 34 
 35         //关闭连接
 36         sd.close();
 37     }
 38 
 39     //升级数据库
 40     public void bt2_OnClick(View v)
 41     {
 42         //使用工具类得到数据库对象
 43         MyDBHelper myDBHelper=new MyDBHelper("test.db",2);
 44 
 45         //得到连接
 46         SQLiteDatabase sd=myDBHelper.getWritableDatabase();
 47 
 48         Toast.makeText(TestActivity2.this, "连接数据库成功", Toast.LENGTH_SHORT).show();
 49 
 50         //关闭连接
 51         sd.close();
 52     }
 53 
 54    
 55 
 56     //实现SQLiteOpenHelper的内部类
 57     class MyDBHelper extends SQLiteOpenHelper
 58     {
 59         //构造方法
 60         public MyDBHelper(String dbname,int ver)
 61         {
 62             //显示调用父类的构造方法
 63             //必须在第一行
 64             super(TestActivity2.this,dbname,null,ver);
 65 
 66         }
 67 
 68         //创建和初始化数据库
 69         @Override
 70         public void onCreate(SQLiteDatabase db) {
 71 
 72             //1.执行创建数据库的语句
 73             String sql="CREATE TABLE t_user" +
 74                     "(_id  INTEGER PRIMARY KEY " +
 75                     "AUTOINCREMENT NOT NULL," +
 76                     "name  VARCHAR(20) NOT NULL," +
 77                     "sex CHAR(1),age  INTEGER)";
 78             db.execSQL(sql);
 79 
 80             Log.e("TAG","表创建成功");
 81             //2.执行初始化数据的语句，insert语句
 82             ContentValues cv=new ContentValues();
 83 
 84             cv.put("name","张三");
 85             cv.put("sex","男");
 86             cv.put("age","20");
 87 
 88             //执行插入,返回主键
 89             long l=db.insert("t_user",null,cv);
 90 
 91             Log.e("TAG","初始化数据="+l);
 92         }
 93 
 94         //升级数据库
 95         //触发条件：当版本号增大
 96         @Override
 97         public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
 98 
 99             //修改数据
100             if(newVersion==2)
101             {
102                 ContentValues cv=new ContentValues();
103                 cv.put("name","李四");
104 
105                 String sql="update t_user set name=\'李四\' where  _id=1 ";
106 
107                 String[] str={"1","18"};
108                 //调用db的更新方法
109                 int i=db.update("t_user", cv, "_id=? and age>?",str);
110 
111                 Log.e("TAG","升级数据 数据条数="+i);
112             }
113 
114         }
115     }
116 }

.java