数据库简单增删改查

MainActivity

       //创建dao层
         dao = new Dao(this);```

Dao层

public class Dao {
 SQLiteDatabase database;
 List<Employer> employers;
 Employer employer;
 //构造方法
    public Dao(Context context){
      Mhelper mhelper = new Mhelper(context);
      database = mhelper.getReadableDatabase();
    }
     //添加
 public void insert(String name, String password) {
  //table: 表名 , 
  //nullColumnHack：可以为空，标示添加一个空行, 
  //values:数据一行的值 , 
  //返回值：代表添加这个新行的Id ，-1代表添加失败
   ContentValues values = new ContentValues();
   values.put("name", name);
   values.put("password", password);
   
   database.insert("emps", null, values);
  
 }
 
 
 //查询
 public List<Employer> query() {
  Cursor cursor = database.rawQuery("select * from emps", null);
  //创建集合
  employers = new ArrayList<Employer>();
  while (cursor.moveToNext()) {
   String names = cursor.getString(cursor.getColumnIndex("name"));
   String pwds = cursor.getString(cursor.getColumnIndex("password"));
   //创建对象
   Employer employer = new Employer("1",names,pwds);
   //加入集合中
   employers.add(employer);
   Log.e("sel", employers.toString());
  }
  
  return employers;
 }
public void update(String edname, String edpwd) {
  //database.execSQL("updata users set name=?,age=? where (name=?)",new Object[]{name,age,tj});
  ContentValues values = new ContentValues();
  //修改的值
  values.put("password", edpwd);
  //table:表名,   values：更新的值, 
  //whereClause:更新的条件, 
  //whereArgs：更新条件的占位符的值,
  //返回值：成功修改多少行
  database.update("emps", values, "name=?", new String[]{edname});
  
 }
public int del(String name) {
     //database.execSQL("delete from users where name=?", new Object[]{name});
   
   ContentValues values = new ContentValues();
     //table ：表名
    //whereClause: 删除条件,
    //whereArgs：条件的占位符的参数 ; 
    //返回值：成功删除多少行
   int result = database.delete("users", "name=?", new String[]{name});
   Log.e("del", "vd"+result);
   database.close();
   
   return result;
    
  }
  

Mhelper类

  public class Mhelper extends SQLiteOpenHelper{
      public Mhelper(Context context) {
         super(context, "emps.db", null, 1);
          // TODO Auto-generated constructor stub
   }
      public void onCreate(SQLiteDatabase db) {
         db.execSQL("create table emp (id integer primary key autoincrement,name text,password text)");
 
 }
 public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
  // TODO Auto-generated method stub
  
 }