db.changeVersion無法按預期方式工作

Question

我正在嘗試在Ubuntu Touch的應用程序中升級數據庫。我使用QtQuick.LocalStorage 2.0。

當我調用db.changeVersion它可以工作，但db.version不會改變，直到應用程序重新啓動。

db.changeVersion(db.version, "2", function(tx){...}); // Update database to version 2 
console.log(db.version); //Should return "2", instead returns previous version of database 

如何在不重新啓動應用程序的情況下新建db.version？

Answer 1

我解決了我寫這個函數的問題，它允許從任何版本的數據庫升級到最新版本，沒有任何問題。

/* We need this function because db.version is in the .ini file, that is update only by Javascript Garbage Collection. 
* So, we have to upgrade from actual version to the last version using only once db.changeVersion. 
* To avoid to have a lot of switch and spaghetti-code, this function allow to add new db version without modify old sql 
* 
* IMPORTANT: NUMBER OF VERSION HAVE TO BE INT (e.g. 0.1, not 0.1.1) 
*/ 
function upgradeDB() { 
    // This is the array with all the sql code, insert your update at the last 
    var sqlcode = [ 
     'CREATE TABLE IF NOT EXISTS Calculations(id INTEGER PRIMARY KEY, calc TEXT)', 
     'ALTER TABLE Calculations ADD insertDate INTEGER NOT NULL DEFAULT 0' 
    ] 

    // This is the last version of the DB, remember to update when you insert a new version 
    var lastVersion = "0.2"; 

    // Hack for change old numeration with new one 
    if (db.version == "0.1.1") { 
     db.changeVersion("0.1.1", "0.2"); 
     console.log("Fixed DB!"); 
    } 

    // So, let's start the version change... 
    db.changeVersion(db.version, lastVersion, 
     function(tx) { 
      if (db.version < 0.1) { 
       tx.executeSql(sqlcode[0]); 
       console.log('Database upgraded to 0.1'); 
      } 
      if (db.version < 0.2) { 
       tx.executeSql(sqlcode[1]); 
       console.log('Database upgraded to 0.2'); 
      } 

      /* This is the structure of the update: 
      * n is the number of version that sql update to 
      * m is the number of the sql element in the array. Remember that the number of the first element of array is 0 ;) 
      if (db.version < n) { 
       tx.executeSql(sqlcode[m]); 
       console.log('Database upgraded to n'); 
      } 
      */ 
     }); // Finish db.changeVersion 
}