Question

我正在尝试为Ubuntu Touch升级应用中的数据库。我使用QtQuick.LocalStorage 2.0。

当我调用db.changeVersion时，它可以工作，但db.version在应用重启之前不会改变。

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

如何在不重新启动应用程序的情况下使用新的db.version？

Answer 1

此问题最近在Qt中修复。现在，changeVersion函数将返回一个新的db对象，该对象的version字段已更新。

https://bugreports.qt.io/browse/QTBUG-71838

以前的Qt版本要求用户重新打开数据库以查看更新的版本，如测试代码所示：

http://code.qt.io/cgit/qt/qtdeclarative.git/tree/tests/auto/qml/qqmlsqldatabase/data/changeversion.js

Answer 2

此错误已修复，请参阅Andrzej的回答

原始回答

我解决了编写此函数的问题，该函数允许从任何版本的DB升级到上一版本而没有问题。

/* 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
}

db.changeVersion无法按预期工作

2 个答案: