Android first---SQLite

SQLite数据库

• 轻量级关系型数据库
• 创建数据库需要使用的api：SQLiteOpenHelper
  • 必须定义一个构造方法：
    
    public MyOpenHelper(Context context, String name, CursorFactory factory, int version){}
    
    //arg1:数据库文件的名字
    
    //arg2:游标工厂
    
    //arg3:数据库版本
  • 数据库被创建时会调用：onCreate方法
  • 数据库升级时会调用：onUpgrade方法

创建数据库

//创建OpenHelper对象
MyOpenHelper oh = new MyOpenHelper(getContext(), "person.db", null, 1);
//获得数据库对象,如果数据库不存在，先创建数据库，后获得，如果存在，则直接获得
SQLiteDatabase db = oh.getWritableDatabase();
    * getWritableDatabase()：打开可读写的数据库
    * getReadableDatabase()：在磁盘空间不足时打开只读数据库，否则打开可读写数据库
    * 在创建数据库时创建表
public void onCreate(SQLiteDatabase db) {
    db.execSQL("create table person (_id integer primary key autoincrement, name char(10), phone char(20), money integer(20))");
}

---

数据库的增删改查

SQL语句

* insert into person (name, phone, money) values ('张三', '159874611', 2000);
* delete from person where name = '李四' and _id = 4;
* update person set money = 6000 where name = '李四';
* select name, phone from person where name = '张三';

执行SQL语句实现增删改查

	//插入
	db.execSQL("insert into person (name, phone, money) values (?, ?, ?);", new Object[]{"张三", 15987461, 75000});
	//查找
	Cursor cs = db.rawQuery("select _id, name, money from person where name = ?;", new String[]{"张三"});
            * 测试方法执行前会调用此方法
	protected void setUp() throws Exception {
		super.setUp();
		//					获取虚拟上下文对象
		oh = new MyOpenHelper(getContext(), "people.db", null, 1);
	}
            ###使用api实现增删改查
            * 插入
	//以键值对的形式保存要存入数据库的数据
	ContentValues cv = new ContentValues();
	cv.put("name", "刘能");
	cv.put("phone", 1651646);
	cv.put("money", 3500);
	//返回值是改行的主键，如果出错返回-1
	long i = db.insert("person", null, cv);

• 删除

    //返回值是删除的行数
    int i = db.delete("person", "_id = ? and name = ?", new String[]{"1", "张三"});
  

• 修改

    ContentValues cv = new ContentValues();
    cv.put("money", 25000);
    int i = db.update("person", cv, "name = ?", new String[]{"赵四"});
  

• 查询

    //arg1:要查询的字段
    //arg2：查询条件
    //arg3:填充查询条件的占位符
    Cursor cs = db.query("person", new String[]{"name", "money"}, "name = ?", new String[]{"张三"}, null, null, null);
    while(cs.moveToNext()){
    	//							获取指定列的索引值
    	String name = cs.getString(cs.getColumnIndex("name"));
    	String money = cs.getString(cs.getColumnIndex("money"));
    	System.out.println(name + ";" + money);
    }
  

事务

• 保证多条SQL语句要么同时成功，要么同时失败

• 最常见案例：银行转账

• 事务api

    try {
    	//开启事务
    	db.beginTransaction();
    	...........
    	//设置事务执行成功
    	db.setTransactionSuccessful();
    } finally{
    	//关闭事务
    	//如果此时已经设置事务执行成功，则sql语句生效，否则不生效
    	db.endTransaction();
    }
  

---

代码展示：

    public class TestCase extends AndroidTestCase {
//此时测试框架还没有初始化完毕，没有虚拟上下文对象
    //private MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
private MyOpenHelper oh;
private SQLiteDatabase db;
public void test(){
	//getContext():获取一个虚拟的上下文
	MyOpenHelper oh = new MyOpenHelper(getContext(), "people.db", null, 1);
	//如果数据库不存在，先创建数据库，再获取可读可写的数据库对象，如果数据库存在，就直接打开
	SQLiteDatabase db = oh.getWritableDatabase();
	//如果存储空间满了，那么返回只读数据库对象
            //SQLiteDatabase db = oh.getReadableDatabase();
}
//测试框架初始化完毕之后，在测试方法执行之前，此方法调用
@Override
protected void setUp() throws Exception {
	super.setUp();
	oh = new MyOpenHelper(getContext(), "people.db", null, 1);
	db = oh.getWritableDatabase();
}
//测试方法执行完毕之后，此方法调用
@Override
protected void tearDown() throws Exception {
	// TODO Auto-generated method stub
	super.tearDown();
	db.close();
}
public void insert(){
	db.execSQL("insert into person (name, salary, phone)values(?, ?, ?)", new Object[]{"小志的老婆[1]", "13000", 138438});
	db.execSQL("insert into person (name, salary, phone)values(?, ?, ?)", new Object[]{"小志的儿子", 14000, "13888"});
	db.execSQL("insert into person (name, salary, phone)values(?, ?, ?)", new Object[]{"小志", 14000, "13888"});
}
public void delete(){
	db.execSQL("delete from person where name = ?", new Object[]{"小志"});
}
public void update(){
	db.execSQL("update person set phone = ? where name = ?", new Object[]{186666, "小志的儿子"});
}
public void select(){
	Cursor cursor = db.rawQuery("select name, salary from person", null);
	while(cursor.moveToNext()){
		//通过列索引获取列的值
		String name = cursor.getString(cursor.getColumnIndex("name"));
		String salary = cursor.getString(1);
		System.out.println(name + ";" + salary);
	}
}
public void insertApi(){
	//把要插入的数据全部封装至ContentValues对象
	ContentValues values = new ContentValues();
	values.put("name", "游天龙");
	values.put("phone", "15999");
	values.put("salary", 16000);
	db.insert("person", null, values);
}
public void deleteApi(){
	int i = db.delete("person", "name = ? and _id = ?", new String[]{"小志的儿子", "3"});
	System.out.println(i);
}
public void updateApi(){
	ContentValues values = new ContentValues();
	values.put("salary", 26000);
	int i = db.update("person", values, "name = ?", new String[]{"游天龙"});
	System.out.println(i);
}
public void selectApi(){
	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"));
		System.out.println(name + ";" + phone + ";" + salary);
	}
}
public void transaction(){
	try{
		//开启事务
		db.beginTransaction();
		ContentValues values = new ContentValues();
		values.put("salary", 12000);
		db.update("person", values, "name = ?", new String[]{"小志"});
		values.clear();
		values.put("salary", 16000);
		db.update("person", values, "name = ?", new String[]{"小志的儿子"});
		int i = 3/1;
		//设置  事务执行成功
		db.setTransactionSuccessful();
	}
	finally{
		//关闭事务，同时提交，如果已经设置事务执行成功，那么sql语句就生效了，反之，sql语句回滚
		db.endTransaction();
	}
}
}