数据库

• 第一步
  创建一个新工程，创建一个class这个class继承于SQLiteOpenHelper这个类，并实现两个方法和一个构造方法

• 第二步：调用SQLiteOpenHelper这个类的构造方法，先创建一个对象，然后调用创建数据库的方法 参数1：许你一个上下文 参数2：数据库名称 参数3：null 参数四：不能小于1；
  MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
  SQLiteDatabase db = oh.getWritableDatabase();//如果数据库不存在，先创建数据库 ，获取一个可读可写数据库对象

• 第三步：创建数据库表
  @Override
  public void onCreate(SQLiteDatabase arg0) {
  //创建数据库表
  arg0.execSQL("create table person(_id integer primary key autoincrement, name char(10),salary char(20),phone integer(20) )");
  }

• 第四步：创建表之后就可以进行表的增删改查了
  public void insert(){
  MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
  SQLiteDatabase db = oh.getWritableDatabase();
  db.execSQL("insert into person(name,salary,phone)values(?,?,?)", new Object[]{"小志志卡","13000",138438});
  db.close();
  }
  public void delete(){
  MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
  SQLiteDatabase db = oh.getWritableDatabase();
  db.execSQL("delete from person where name = ?", new Object[]{"小志"});
  db.close();
  }

  public void updata(){
  MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
  SQLiteDatabase db = oh.getWritableDatabase();
  db.execSQL("update person set phone = ? where name = ?", new Object[]{123,"小志志卡"});
  db.close();
  }

• 上面的方法容易出错，可以用封装好的api来进行增删改查
  public void deleteApi(){
  MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
  SQLiteDatabase db = oh.getWritableDatabase();
  int i = db.delete("person", "name = ?", new String[]{"游天龙"});
  db.close();
  }

  public void updateApi(){
  ContentValues values = new ContentValues();
  values.put("salary", 1300);
  MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
  SQLiteDatabase db = oh.getWritableDatabase();
  db.update("person", values, "name = ?", new String[]{"游天龙"});
  db.close();
  }

  public void selectApi(){
  ContentValues values = new ContentValues();
  values.put("salary", 1300);
  MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
  SQLiteDatabase db = oh.getWritableDatabase();
  Cursor cursor = db.query("person", null, null, null, null, null, null, null);
  while (cursor.moveToNext()) {
  String name = cursor.getString(cursor.getColumnIndex("name"));
  String phone = cursor.getString(cursor.getColumnIndex("phone"));
  String salary = cursor.getString(cursor.getColumnIndex("salary"));
  }
  db.close();
  }

• 事务：要成功一起成功，要失败都失败
  public void transaction(){
  MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
  SQLiteDatabase db = oh.getWritableDatabase();

    db.beginTransaction();
    ContentValues values = new ContentValues();
    values.put("salary", 12000);
    db.update("person", values, "name = ?", new String[]{"小志卡"});
    
    values.clear();
    values.put("salary", 14000);
    db.update("person", values, "name = ?", new String[]{"小志志卡"});
    db.setTransactionSuccessful();
    db.endTransaction();
    db.close();
}