Android开发之通过Android的API对sqlite数据库的操作以及数据库事务的练习

Posted 2021-03-11 酸奶面包

一、通过android的API对sqlite数据库的操作

通过已有的ContentValues类，实例一个对象value来调用其中内部的方法来操作sqlite数据库

代码：

package com.example.databasedemo;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

/**
 * 这个类用于对数据库的增删改查
 */
public class Dao {

    private final DatabaseHelper mHelper;
    private static final String TAG="Dao";
    public Dao(Context context){

        //创建数据库
        //Ctrl+Alt+F,之后加回车，创建成员变量
        mHelper = new DatabaseHelper(context);

    }

    public  void insert(){
        SQLiteDatabase db = mHelper.getWritableDatabase();
//        String sql="insert into "+Constants.TABLE_NAME+"(_id,name,age,salary,phone) values(?,?,?,?,?)";
//        Object []obj={1,"haohao",20,10000};
//        db.execSQL(sql,obj);
        ContentValues values  =new ContentValues();
        //插入数据
        values.put("_id",2);
        values.put("name","me");
        values.put("age",20);
        values.put("salary",5);
        db.insert(Constants.TABLE_NAME,null,values);
        db.close();
    }

    public  void delete(){
        SQLiteDatabase db = mHelper.getWritableDatabase();
//        String sql="delete from "+Constants.TABLE_NAME+" where name = ?";
//        Object []obj={"hao"};
//        db.execSQL(sql,obj);
        int result = db.delete(Constants.TABLE_NAME, null, null);
        Log.d(TAG,"result="+result);
        db.close();
    }

    public  void update(){
        SQLiteDatabase db = mHelper.getWritableDatabase();
//        String sql="update "+Constants.TABLE_NAME+" set salary= ? where name = ?";
//        Object []obj={3,"hao"};
//        db.execSQL(sql,obj);
        ContentValues values = new ContentValues();
        values.put("salary",54321);
        db.update(Constants.TABLE_NAME,values,null,null);
        db.close();
    }

    public  void query(){
        SQLiteDatabase db = mHelper.getWritableDatabase();
//        String sql="select * from "+Constants.TABLE_NAME+" where name = ?";
//        String []obj={"hao"};
//        Cursor cursor = db.rawQuery(sql, obj);
//        while (cursor.moveToNext()){
//            String name = cursor.getString(cursor.getColumnIndex("name"));
//            String age = cursor.getString(cursor.getColumnIndex("age"));
//            Log.d(TAG,"名字："+name+"年龄："+age);
//        }
//        cursor.close();

        Cursor cursor = db.query(Constants.TABLE_NAME, null, null, null, null, null, null);

        while (cursor.moveToNext()){
            int id = cursor.getInt(0);
            String name = cursor.getString(1);
            Log.d(TAG,"ID="+id+"name="+name);
        }



        cursor.close();
        db.close();
    }
}

ContentValues

 

 

 

 

二、数据库事务

package com.example.transcationdemo;

import androidx.appcompat.app.AppCompatActivity;

import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

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

        DatabaseHelper helper =new DatabaseHelper(this);
        helper.getWritableDatabase();
        //   toTestInsert();
        toTestUpdate();
    }

    public void toTestInsert(){
        DatabaseHelper helper=new DatabaseHelper(getApplicationContext());
        SQLiteDatabase db=helper.getWritableDatabase();

        db.execSQL("insert into givemoney values( 1 , ‘company‘, 100000)");


        db.execSQL("insert into givemoney values( 2 , ‘me‘, 0)");

        db.close();
    }

    public void toTestUpdate(){
        DatabaseHelper helper =new DatabaseHelper(getApplicationContext());
        SQLiteDatabase db=helper.getWritableDatabase();

        db.beginTransaction();
        try {

             db.execSQL("update givemoney set money = 100000-12000 where name = ‘company‘");
            int a=10/0;
            db.execSQL("update givemoney set money = 12000 where name = ‘me‘");
            db.setTransactionSuccessful();
        } catch (SQLException e) {

        }finally {


            db.endTransaction();
            db.close();
        }


    }
}

Transcation

两个特点

1、安全性

通过Try{}Catch{}的进行，保证一次性将Try中的内容全部执行，避免数据丢失和运算的错误。

2、高效性

事务：先将数据写入内存，然后一次写入数据库。

普通：打开数据库，存入数据，关闭数据库。