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Talk:How-to create a persistent settings database in Qt Quick (QML)

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Molbal - Really useful

It's really really useful, just what I was looking for

molbal 22:25, 10 August 2011 (EEST)

Geytjie - sql on Symbian

Hi, really like the idea. Can one use this with a mySql database, or does one need to install sqlite if you need to develop the application for Symbian celphones? And do I need to replace function getDatabase() { return openDatabaseSync("WineGui", "1.0", "StorageDatabase", 100000); } with my dbname, like this?

function getDatabase() { return openDatabaseSync("LollaGui", "1.0", "LollaDb", 100000);

}

geytjie 21:52, 19 September 2011 (EEST)

Slocan -

@geytjie: This only works with sqlite databases. You do not need to install sqlite, it is included with Qt/QML, so this works on Symbian (as well as other platforms where Qt/QML works).

return openDatabaseSync("LollaGui", "1.0", "LollaDb", 100000);

would be correct, as you replaced the AppName.

Slocan 00:50, 3 November 2011 (EET)

Adrianomgil - Sqlite Access inside C++ context

How can I share the same sqlite database between C++ and QML contexts? My problem is about the crazy filename the offline storage create using md5.

Is there a way to change such name?

adrianomgil 22:49, 21 November 2011 (EET)

Hamishwillee - Adrianomgil - try the forums

Hi Adrian

Well, you can always run the query QML side and share the results using any of the sharing methods. No idea if you can actually access the file in C++ - suggest you raise this on the discussion boards in order to get more "eyes" on the problem. If you find a good way of doing this, would be great to extend the article though.

Regards

Hamish

hamishwillee 01:37, 22 November 2011 (EET)

Texrat - Can't import js file

I saved the storage.js file to the project root folder, but my MeeGo Harmattan project is unable to import it. Any idea why that would happen?

Texrat 00:13, 5 December 2011 (EET)

Never mind-- wrong folder! moved to project subfolder under QML and it works fine.

Hamishwillee - This is useful

I like this article, but it doesn't show everything you might want to do with a database.

There is some more comprehensive code, in the context of a real application, in the articles links from here: http://www.developer.nokia.com/Community/Blogs/blog/nokia-developer-news/2011/11/25/new-guides-and-code-step-through-qt-quick-development-for-desktop-and-symbian

These shows some more complicated settings objects, and how these can be pulled in and out of QML databases into models.

hamishwillee 02:16, 5 December 2011 (EET)

Itapadar - Is it Ok to use the default database path ?

Hi,

Is it Ok, to use the default database path of the OfflinestorageApi? Does it use the mass storage or RAM?

I tried setting the OfflineStoragePath, but it doesnt create the databse for me , despite creating the directory structure I want.

{ if (dir.mkpath(QString(customPath))){

       viewer.engine()->setOfflineStoragePath(customPath);
   }

}

Also, it returns the desired path when I print with, viewer.engine()->offlineStoragePath(), but it creates and saves the database in some other folder.

Regards

itapadar 13:04, 18 January 2012 (EET)

Tslv - how to populate DB?

Hi, Thanks for the example.

1. What if I want to distribute my app with some data already inside? Let's say I've got list of stores that sell toys. How do I populate my database? Do I write an app that creates database and allows me to put stores inside? :) There must be a better way to do this.

2. Where is this database stored? Inside a file? Which one?

tslv 11:48, 23 January 2012 (EET)

Kwhitefoot - There seems to be some confusion about the name of the database

There seems to be some confusion about where the files are created and some people seem to think that it is important to avoid name collisions, or at least they give that impression.

However, at least on the N9, it doesn't actually matter what you call it unless you have more than one used by the same application because the files are stored in:

/home/user/.local/share/data/${organization-name}/${app-name}/QML/OfflineStorage/Databases/

These two variables can be set in main:

   QApplication::setApplicationName(app-name);
   QApplication::setOrganizationName(organization-name);
Can anyone give some clear rules about this? The documentation doesn't make it clear what name needs to be used and some projects targetting the N9 use very generic names like "SettingsDB" (Buienradar).

kwhitefoot 22:16, 3 November 2012 (EET)

Hamishwillee - I think it matters if you want to be cross platform

According to the docs in QML global object: "These databases are user-specific and QML-specific, but accessible to all QML applications. They are stored in the Databases subdirectory of QDeclarativeEngine::offlineStoragePath(), currently as SQLite databases."

Symbian doesn't have a "public" user specific space, so as I understand it they are in a shared area of the drive (you can check the location here: http://doc.qt.nokia.com/4.7/qdeclarativeengine.html#offlineStoragePath-prop ). If so, its quite possible that name classes could occur. I haven't tried this though - so you'd have to look in the folder (possibly data/QML/OfflineStorage/Databases/ ) .

Note that if you're worried you can set your own path for offline storage to avoid any possible conflicts.

As you say, not an issue on N9 since you get a org and app name specific folder.

hamishwillee 07:45, 6 November 2012 (EET)

Kwhitefoot - Avoiding conflicts for cross platform applications.

Then I think that the right thing to do is to add the organization and app name to the database name. that should pretty much eliminate name collisions.

For instance if I made an application called FileMan I might use:

 organization name = kwhitefoot 
 app-name = FileMan

giving a settings file name of

 kwhitefoot-FileMan-settings
It's probably a good idea to avoid spaces too.

kwhitefoot 16:08, 6 November 2012 (EET)

Hamishwillee - Yes it should

Yes, adding the app and org name should sort out the issue.

It's probably a good idea to avoid spaces too.

Symbian won't care

Regards

Hamish

hamishwillee 07:57, 7 November 2012 (EET)

 

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