数据库入门---增删改查

使用google提供的另外一种方式操作数据库表：


1、插入数据
public void insert(View v){

//db.execSQL("insert into person (name)values(?)", new String[]{"lisi"});
 ContentValues values = new ContentValues();
 Random r = new Random();
 values.put("name", "zhangsan"+r.nextInt(100));
  long rowId =  db.insert("person", null, values);
 System.out.println("rowId="+rowId);
Toast.makeText(this, "插入数据成功", 0).show();
}
  
  2、查询数据
public void query(View v){
  /**
  * table 表名
  * columns 查询的列
  * selection 查询条件"id=1"
  * selectionArgs 查询条件的值
  * String groupBy
  * String having
       * String orderBy
  * 
  */
 Cursor cursor = db.query("person", new String[]{"id","name" }, null, null, null, null, null);
 
 while(cursor.moveToNext()){
int id = cursor.getInt(0);
String name = cursor.getString(1);
 
System.out.println("id="+id+"; name="+name);
 }

 Toast.makeText(this, "查询数据成功", 0).show();
}

    3.修改数据

     public void update(View v){

// db.execSQL("update person set name='wangwu' where id=?", new Object[]{1});
//用来封装要修改的列名和值
 ContentValues values = new ContentValues();
 values.put("name", "wangwu");
 db.update("person", values, "id=?", new String[]{"1"});
 Toast.makeText(this, "更新数据成功", 0).show();

}
  4.删除数据
        public void delete(View v){

// db.execSQL("delete from person where id=?", new Object[]{1});
   db.delete("person", "id=?", new String[]{"2"});
Toast.makeText(this, "删除数据成功", 0).show();

}
  5.  代码例子

1.Dao层的方法封装

package com.example.asus.db;import android.content.ContentValues;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.util.Log;/** * Created by ASUS on 2017/5/16. */public class Dao {    private static final String TAG ="MyActivity";    private DBOpenHelper dbOpenHelper;    public Dao(Context context)    {        dbOpenHelper=new DBOpenHelper(context);    }    public  boolean add(Student student)    {        SQLiteDatabase db=dbOpenHelper.getReadableDatabase();       // db.execSQL("insert into student (name,phone) values (?,?);",new Object[]{student.name,student.phone});        //   表名  null表示添加一个空行   values 表示添加的一行的值        ContentValues values=new ContentValues();   // 是使用 map 封装,来存放值        values.put("name",student.name);        values.put("phone",student.phone);        // 返回值表示新一行的行id     -1     表示添加失败        long result= db.insert("student",null,values);     //这种方法有返回值        db.close();        if (result!=-1)        {         return  true;        }        else            return false;    }    public  int  del(String name)    {        SQLiteDatabase db=dbOpenHelper.getReadableDatabase();        //db.execSQL("delete from student where name=?;",new Object[]{name});        //   表名   where 删除条件        int result=db.delete("student","name=?",new String[]{name});        //返回值表示成功删除多少行        db.close();        return result;    }    public  int update(Student student)    {        SQLiteDatabase db=dbOpenHelper.getReadableDatabase();       // db.execSQL("update  student  set phone=? where name=?;",new Object[]{student.name,student.phone});        //        ContentValues values=new ContentValues();// 是用map封装,来存放值        values.put("name",student.name);        int result=db.update("student",values,"name=?",new String[]{student.name});        db.close();        //  返回值表示成功修改多少行        return result;    }    public  void query(String name)    {        SQLiteDatabase db=dbOpenHelper.getReadableDatabase();       // Cursor cursor=db.rawQuery("select _id,name,phone from student where name=?",new String[]{name});       Cursor cursor = db.query("student",null,"name=?",new String[]{name},null,null,"_id");        //这个方法没有第一种灵活，表名是写死的        //  null  查询所有的        if (cursor!=null&&cursor.getCount()>0)        {          while (cursor.moveToNext())          {              int id=cursor.getInt(0);              String name1 = cursor.getString(1);              String phone =cursor.getString(2);              Log.i(TAG,"_id:"+id+";name:"+name1+";phone:"+phone);          }          cursor.close();        }        db.close();    }}

2.Activity中的具体操作

package com.example.asus.db;import android.app.Activity;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.os.Bundle;import android.view.View;import android.widget.Toast;public  class MainActivity extends Activity {    private Context context;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        context = this;        DBOpenHelper dbopenhelper = new DBOpenHelper(context);        SQLiteDatabase db = dbopenhelper.getReadableDatabase();         findViewById(R.id.Button).setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 Dao dao = new Dao(context);                 Student student2 = new Student();                 student2.name = "向++";                 student2.phone = "10086";                 boolean result=dao.add(student2);                 if (result) {                     Toast.makeText(MainActivity.this, "添加成功", Toast.LENGTH_LONG).show();                 }                 else  {                     Toast.makeText(MainActivity.this, "GG", Toast.LENGTH_LONG).show();                 }             }         });         findViewById(R.id.Button1).setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 Dao dao = new Dao(context);                int result= dao.del("向++");                 Toast.makeText(MainActivity.this,"成功删除"+result+"行",Toast.LENGTH_LONG).show();             }         });        findViewById(R.id.Button2).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                Dao dao = new Dao(context);                Student student2=new Student();                student2.name="周++";                student2.phone="10010";                int result=dao.update(student2);                Toast.makeText(MainActivity.this,"你成功更新"+result+"行",Toast.LENGTH_LONG).show();            }        });        findViewById(R.id.Button3).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                Dao dao = new Dao(context);                dao.query("向++");                dao.query("周++");                Toast.makeText(MainActivity.this,"GG",Toast.LENGTH_LONG).show();            }        });    }}