Android开发：SQLite数据库操作

zhaoshuliok

2011-09-21

Android中内置的是SQLite小型数据库,类似access一样是以文件方式存在的,操作起来十分方便。android操作SQLite需要继承自SQLiteOpenHelper 来得到连接。实现了2个方法:onCreate和onUpgrade。第一次获得对数据库的读或写操作的时候调用onCreate,所以这里面写创建数据表的语句;在数据库版本变化的时候会调用onUpgrade,所以如果表结构变化了就在这里修改。

下面的代码继承了SQLiteOpenHelper ,并且自己写了几个增删改查方法,将对数据库操作的DAO模块继承到一起,以后操作数据库用这一个java文件基本就OK啦。

package cn.itcast.service;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBOpenHelper extends SQLiteOpenHelper {
private static final String DATABASENAME = "test.db"; //数据库名称
private static final int DATABASEVERSION = 1;//数据库版本,大于0
public DBOpenHelper(Context context) {
super(context, DATABASENAME, null, DATABASEVERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE person (personid integer primary key autoincrement, name varchar(20), amount integer)");//执行有更改的sql语句
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS person");
onCreate(db);
}
public void payment(){
SQLiteDatabase db = getWritableDatabase();
db.beginTransaction();//事启事务
try{
db.execSQL("update person set amount=amount-10 where personid=?", new Object[]{1});
db.execSQL("update person set amount=amount+10 where personid=?", new Object[]{2});
db.setTransactionSuccessful();//设置事务标志为成功，当结束事务时就会提交事务
}finally{
db.endTransaction();
}
}
public void save(Person person){
//如果要对数据进行更改，就调用此方法得到用于操作数据库的实例,该方法以读和写方式打开数据库
SQLiteDatabase db = getWritableDatabase();
db.execSQL("insert into person (name,amount) values(?,?)",
new Object[]{person.getName(),person.getAmount()});
}
public void update(Person person){
SQLiteDatabase db = getWritableDatabase();
db.execSQL("update person set name=? where personid=?",
new Object[]{person.getName(),person.getId()});
}
public void delete(Integer id){
SQLiteDatabase db = getWritableDatabase();
db.execSQL("delete from person where personid=?", new Object[]{id.toString()});
}
public Person find(Integer id){
//如果只对数据进行读取，建议使用此方法
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.rawQuery("select * from person where personid=?", new String[]{id.toString()});//得到游标
if(cursor.moveToFirst()){
int personid = cursor.getInt(cursor.getColumnIndex("personid"));
String name = cursor.getString(cursor.getColumnIndex("name"));
int amount = cursor.getInt(cursor.getColumnIndex("amount"));
Person person = new Person(personid, name);
person.setAmount(amount);
return person;
}
return null;
}
public List<Person> getScrollData(Integer offset, Integer maxResult){
List<Person> persons = new ArrayList<Person>();
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.rawQuery("select * from person limit ?,?",
new String[]{offset.toString(), maxResult.toString()});
while(cursor.moveToNext()){
int personid = cursor.getInt(cursor.getColumnIndex("personid"));
String name = cursor.getString(cursor.getColumnIndex("name"));
int amount = cursor.getInt(cursor.getColumnIndex("amount"));
Person person = new Person(personid, name);
person.setAmount(amount);
persons.add(person);
}
cursor.close();
return persons;
}
public Cursor getCursorScrollData(Integer offset, Integer maxResult){
SQLiteDatabase db = getReadableDatabase();
return db.rawQuery("select personid as _id, name, amount from person limit ?,?",
new String[]{offset.toString(), maxResult.toString()});
}
public long getCount() {
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.rawQuery("select count(*) from person", null);
cursor.moveToFirst();
return cursor.getLong(0);
}
}