Hello Android - SQLite数据库操作

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);
	}
}

涉及到的bean

class Person {
	private Integer id;
	private String name;
	private Integer amount;
	
	public Integer getAmount() {
		return amount;
	}

	public void setAmount(Integer amount) {
		this.amount = amount;
	}

	public Person(){}
	
	public Person(Integer id, String name) {
		this.id = id;
		this.name = name;
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}

	@Override
	public String toString() {
		return "Person [amount=" + amount + ", id=" + id + ", name=" + name
				+ "]";
	}

}