思維:

1.當然，它是基于SQLiteOpenHelper.onCreate(第一個呼叫建立)、onUpdate(當所謂的升級計劃)

2.用"腳本"(腳本制作詳細方法問度娘)做數據庫升級,文件名稱標識相應版本號,java中依據“上一版本號、當前版本號”選擇運行的腳本。

升級時,改動DB_VERSION(當前版本號)就可以。

DBManager.java:

package com.example.test;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.InputStream;

import android.content.Context;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;

public class DBManager extends SQLiteOpenHelper {

private final static String DBNAME = "mydata.db";

private final static int DB_VERSION = 1;

private static DBManager instance;

public DBManager(Context context) {

// TODO Auto-generated constructor stub

super(context, DBNAME, null, DB_VERSION);

}

public static DBManager getThis() {

if (instance == null)

instance = new DBManager(MainActivity.getThis());

return instance;

}

@Override

public void onCreate(SQLiteDatabase db) {

// TODO Auto-generated method stub

initDb(db, 0, DB_VERSION);

}

@Override

public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

// TODO Auto-generated method stub

initDb(db, oldVersion, newVersion);

}

// 初始化db,運行腳本

// 注:1>運行"(oldV,newV]"(全新安裝時,oldV=0)間的腳本

// 2>缺失的腳本會直接跳過

private void initDb(SQLiteDatabase db, int oldVersion, int newVersion) {

for (int i = oldVersion + 1; i <= newVersion; i++)

execDBScript(db, "db/update" + i + ".sql");

}

// 運行腳本

private void execDBScript(SQLiteDatabase db, String assetName) {

try {

InputStream is = MainActivity.getThis().getAssets().open(assetName);

String stats = read(is);

execSqls(db, stats);

} catch (Exception e) {

// TODO: handle exception

e.printStackTrace();

}

}

// 批運行,用";"隔開

private void execSqls(SQLiteDatabase db, String stats) {

// onCreate/onUpdate內部已帶事務,多層嵌套無影響(最外層起作用)

db.beginTransaction();

String[] sqls = stats.split(";");

for (int i = 0; i < sqls.length; i++) {

String sqlStatement = sqls[i].trim();

// TODO You may want to parse out comments here

if (sqlStatement.length() > 0) {

// 捕獲錯誤,防止運行drop時 直接越過

try {

db.execSQL(sqlStatement + ";");

} catch (Exception e) {

// TODO: handle exception

e.printStackTrace();

}

}

}

db.setTransactionSuccessful();

db.endTransaction();

}

public static String read(InputStream instream) throws IOException {

ByteArrayOutputStream bos = new ByteArrayOutputStream();

byte[] buffer = new byte[1024];

int len = 0;

while ((len = instream.read(buffer)) != -1) {

bos.write(buffer, 0, len);

}

String ret = new String(bos.toByteArray());

return ret;

}

}

db腳本:

總結

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