Android之数据库操作

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
     */
    @Override
    public 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
     */
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        if(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