实例二

关于sqlite

sqlite是嵌入式SQL数据库引擎SQLite（SQLite Embeddable SQL Database Engine）的一个扩展。SQLite是一个实现嵌入式SQL数据库引擎小型C语言库（C library），实现了独立的，可嵌入的，零配置的SQL数据库引擎。特性包括：事务操作是原子，一致，孤立，并且持久的，即使在系统崩溃和电源故障之后。 零配置——不需要安装和管理。 实现了绝大多数SQL92标准。

 

我在多年前就关注sqlite的发展,非常看好sqlite的前景,因为在移动,嵌入式的应用里面,sqlite具有非常好的特性来满足需求.

早在symbian 9.0 之前,openc 出来后,我就研究sqlite到symbian的移植.后来symbian9.3 nokia就已经集成了sqlite.

至今j2me还不支持sqlite,可以说是个遗憾.

 

现在我们来看看android sqlitedatabase 包里面的关键api

static      SQLiteDatabase  openOrCreateDatabase(String path, SQLiteDatabase.CursorFactory factory)
打开数据库

Cursor  query(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit)
执行查询SQL

void    execSQL(String sql)
执行非查询sql
sdk 1.0 关于cursor和sqlite的相关api对于前面的版本改变很多.

我觉得关键是没了query(String sql)这个简单的方法了.很不爽.

 

不过如果你对新的query方法了解深入点,发现其实也就一样.

我们来看2个例子

//执行select type,name from sqlite_master where name='colaconfig'
String col[] = {"type", "name" };
            Cursor c =db.query("sqlite_master", col, "name='colaconfig'", null, null, null, null);
            int n=c.getCount();
//执行多表查询
//select fee,desc from acctite a,bills b where a.id=b.id 
String col2[] = {"fee", "desc" };
            Cursor c2 =db.query("acctitem a,bills b", col, "a.id=b.id", null, null, null, null);
            int n2=c2.getCount();       
            Log.v("cola","c2.getCount="+n2+"");
            
            c2.moveToFirst(); 
            int k = 0;
                while(!c2.isAfterLast()){
                String ss = c2.getString(0) +", "+ c2.getString(1);              
                c2.moveToNext(); 
                
                Log.v("cola","ss="+ss+"");
            }
 现在来看看我们如何在这个理财工具里面应用它.

我们需要在程序的第一次启动时,创建数据库,然后把基本的表创建好,并且初始化好账目表.

对于上一篇中的initapp方法 ,我们需要改造成

    public void initApp(){
         BilldbHelper billdb=new BilldbHelper(this);
         billdb.FirstStart();
         billdb.close();
         
    }
下面我们给出BilldbHelper.java 代码

package com.cola.ui; import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.util.Log; /** * Provides access to a database of notes. Each note has a title, the note * itself, a creation date and a modified data. */ public class BilldbHelper { private static final String TAG = "Cola_BilldbHelper"; private static final String DATABASE_NAME = "cola.db"; SQLiteDatabase db; Context context; BilldbHelper(Context _context) { context=_context; db=context.openOrCreateDatabase(DATABASE_NAME, 0, null); //创建数据库 Log.v(TAG,"db path="+db.getPath()); } public void CreateTable_acctitem() { try{ db.execSQL("CREATE TABLE acctitem (" //创建账目表 + "ID INTEGER PRIMARY KEY," + "PID integer," + "NAME TEXT," + "TYPE INTEGER" + ");"); Log.v("cola","Create Table acctitem ok"); }catch(Exception e){ Log.v("cola","Create Table acctitem err,table exists."); } } public void CreateTable_bills() { try{ db.execSQL("CREATE TABLE bills (" + "ID INTEGER PRIMARY KEY," + "fee integer," + "userid integer," + "sdate TEXT," + "stime TEXT," + "desc TEXT" + ");"); Log.v("cola","Create Table acctitem ok"); }catch(Exception e){ Log.v("cola","Create Table acctitem err,table exists."); } } public void CreateTable_colaconfig() { try{ db.execSQL("CREATE TABLE colaconfig (" + "ID INTEGER PRIMARY KEY," + "NAME TEXT" + ");"); Log.v("cola","Create Table colaconfig ok"); }catch(Exception e){ Log.v("cola","Create Table acctitem err,table exists."); } } public void InitAcctitem() { db.execSQL("insert into acctitem values (100,0,'收入',0)"); db.execSQL("insert into acctitem values (100100,100,'工资',0)"); db.execSQL("insert into acctitem values (200,0,'支出',1)"); db.execSQL("insert into acctitem values (200100,200,'生活用品',1)"); db.execSQL("insert into acctitem values (200101,200,'水电煤气费',1)"); db.execSQL("insert into acctitem values (200103,200,'汽油费',1)"); Log.v("cola","insert into ok"); } public void QueryTable_acctitem(){ } public void FirstStart(){ //如果是第一次启动,就不存在colaconfig这张表. try{ String col[] = {"type", "name" }; Cursor c =db.query("sqlite_master", col, "name='colaconfig'", null, null, null, null); int n=c.getCount(); if (c.getCount()==0){ CreateTable_acctitem(); CreateTable_colaconfig(); CreateTable_bills(); InitAcctitem(); } Log.v("cola","c.getCount="+n+""); }catch(Exception e){ Log.v("cola","e="+e.getMessage()); } } public void close(){ db.close(); } }