安卓数据库帮助类

/*** 数据库帮助类，用于管理数据库* @author Administrator**/
public class PersonSQLiteOpenHelper extends SQLiteOpenHelper {private String tag="PersonSQLiteOpenHelper";public PersonSQLiteOpenHelper(Context context) {//数据库名，数据库版本号super(context, "zj.db", null, 2);// TODO Auto-generated constructor stub}/*** 数据库第一次创建时调用此方法*/@Overridepublic void onCreate(SQLiteDatabase db) {// TODO Auto-generated method stub//操作数据库String sql="create table person(_id integer primary key,name varchar(20),age integer);";db.execSQL(sql);}/*** 更新数据库的内容*/@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {// TODO Auto-generated method stubif(oldVersion==1&&newVersion==2){Log.i(tag, "数据库更新了");//在表中添加一个余额列db.execSQL("alter table person add balance interger;");}else if(oldVersion==2&&newVersion==3){//其他操作}}}

其中onCreate只在第一次创建是调用，OnUpergrade在数据库版本号升级，如要修改数据库，为数据库增加一列，或删除一列的情况下使用

数据库操作

打开数据库

private PersonSQLiteOpenHelper mOpenHelper;//数据库帮助类public PersonDao(Context context){mOpenHelper = new PersonSQLiteOpenHelper(context);}

由mOpenHelper得到数据库

SQLiteDatabase db= mOpenHelper.getWritableDatabase();

此时可设置版本号,便会根据版本号调用OnUpgrate

         db.getVersion();db.setVersion(2);

对数据库增删改查有两种方式

插入数据 ,直接用SQL语句

public void insert(Person person){SQLiteDatabase db= mOpenHelper.getWritableDatabase();if(db.isOpen()){//执行添加的操作db.execSQL("insert into person(name, age) values(?, ?);",new Object[]{person.getName(),person.getAge()});db.close();}}

插入数据方法二

public void insert(Person person){SQLiteDatabase db= mOpenHelper.getWritableDatabase();if(db.isOpen()){ContentValues values=new ContentValues();values.put("name", person.getName());values.put("age", person.getAge());//执行添加的操作long id=db.insert("person", null, values);Log.i(tag, "id:"+id);db.close();}}

第一种方法删除与更新

public void delete(int id){SQLiteDatabase db= mOpenHelper.getWritableDatabase();if(db.isOpen()){db.execSQL("delete from person where _id = ?;",new Integer[]{id});//执行添加的操作db.close();}}public void update(int id,String name){SQLiteDatabase db= mOpenHelper.getWritableDatabase();if(db.isOpen()){db.execSQL("update person set name = ? where id = ?;",new Object[]{name,id});//执行添加的操作db.close();}}

第二种方法删除与更新

public void delete(int id){SQLiteDatabase db= mOpenHelper.getWritableDatabase();if(db.isOpen()){//执行添加的操作String whereClause=" _id = ?";String []whereArgs={id+""};int count=db.delete("person", whereClause,whereArgs );Log.i(tag, "count="+count+"行");db.close();}}public void update(int id,String name){SQLiteDatabase db= mOpenHelper.getWritableDatabase();if(db.isOpen()){//执行添加的操作ContentValues values=new ContentValues();values.put("name", name);int count=db.update("person", values, "_id=?", new String[]{id+""});Log.i(tag, "修改了count="+count+"行");db.close();}}

第一种方法查询一项与查询所有

public List<Person> queryAll(){SQLiteDatabase db= mOpenHelper.getReadableDatabase();if(db.isOpen()){Cursor cursor= db.rawQuery("select * from person;", null);if(cursor!=null&&cursor.getCount()>0){List<Person> personList=new ArrayList<Person>();int id;String name;int age;while(cursor.moveToNext()){id=cursor.getInt(0);name=cursor.getString(1);age=cursor.getInt(2);personList.add(new Person(id, name, age));}db.close();return personList;}db.close();}return null;}public Person queryItem(int id){SQLiteDatabase db= mOpenHelper.getReadableDatabase();if(db.isOpen()){Cursor cursor= db.rawQuery("select * from person where id= ?;", new String []{id+""});if(cursor!=null&&cursor.moveToFirst()){int id1=cursor.getInt(0);String name=cursor.getString(1);int age=cursor.getInt(2);db.close();return new Person(id1,name,age);}db.close();}return null;}

第二种方法查询数据库

public List<Person> queryAll(){SQLiteDatabase db= mOpenHelper.getReadableDatabase();if(db.isOpen()){String [] columns={"_id","name","age"};String selection=null;String[] selectionArgs=null;String groupBy=null;String having=null;String orderBy=null;Cursor cursor=db.query("person", columns, selection, selectionArgs, groupBy, having, orderBy);int id;String name;int age;if(cursor!=null&&cursor.getCount()>0){List<Person> personList=new ArrayList<Person>();while(cursor.moveToNext()){//向下移一位id=cursor.getInt(0);name=cursor.getString(1);age=cursor.getInt(2);personList.add(new Person(id,name,age));}db.close();return personList;}db.close();}return null;}public Person queryItem(int id){SQLiteDatabase db= mOpenHelper.getReadableDatabase();if(db.isOpen()){String [] columns={"_id","name","age"};String selection="_id=?";String[] selectionArgs={id+""};String groupBy=null;String having=null;String orderBy=null;Cursor cursor=db.query("person", columns, selection, selectionArgs, groupBy, having, orderBy);int _id;String name;int age;if(cursor!=null&&cursor.moveToFirst()){_id=cursor.getInt(0);name=cursor.getString(1);age=cursor.getInt(2);db.close();return new Person(_id,name,age);}db.close();}return null;}

数据库的事务，防止多线程并发操作

public void testTransaction(){PersonSQLiteOpenHelper openHelper=new PersonSQLiteOpenHelper(getContext());SQLiteDatabase db= openHelper.getWritableDatabase();if(db.isOpen()){try{//开户事务db.beginTransaction();//执行业务逻辑db.execSQL("update person set balance =balance -1000 where name='zhangsan';");//ATM机损坏//int result=10/0;db.execSQL("update person set balance =balance +1000 where name='lisi';");//标记事务成功db.setTransactionSuccessful();}finally{//停止事务db.endTransaction();}db.close();}}public void testTransationInsert(){PersonSQLiteOpenHelper openHelper=new PersonSQLiteOpenHelper(getContext());SQLiteDatabase db= openHelper.getWritableDatabase();if(db.isOpen()){//记录当前时间long start=System.currentTimeMillis();//开始添加数据try{db.beginTransaction();for(int i=0;i<10000;i++){db.execSQL("insert into person(name, age, balance) values('wang" + i + "', " + (10 + i) + ", " + (10000 + i) + ")");            }db.setTransactionSuccessful();}finally{db.endTransaction();}//记住结束时间,计算耗时long end=System.currentTimeMillis();long diff=end-start;Log.i(tag, "耗时:"+diff+"ms");db.close();}}

Android数据库基本操作完成