@davidesalvetti Hmm, I am not very confident in your solution. I would create a helper class to create/use right connection according to current thread. Something like this (it is just a skeleton, not sure it is working as it is): #include <QSqlDatabase> #include <QThread> class MyBDConnection { QString m_dbPath; QString m_dbName; Q_DISABLE_COPY(MyBDConnection) public: explicit MyBDConnection(const QString &sqlitePath, const QString &cnxName): m_dbPath(sqlitePath), m_dbName(cnxName) {} QSqlDatabase getDBConnection() { // Starting with Qt 5.11, sharing the same connection between threads is not allowed. // Use a dedicated connection for each thread requiring access to the database, // using the thread address as connection name. QSqlDatabase cnx; QString dbName = QStringLiteral("%1_%2").arg(m_dbName).arg(qintptr(QThread::currentThreadId()), 0, 16); if(QSqlDatabase::contains(dbName)) { cnx = QSqlDatabase::database(dbName); } else { cnx = QSqlDatabase::addDatabase(QStringLiteral("QSQLITE"), dbName); cnx.setDatabaseName(m_dbPath); if (!cnx.isValid() || !cnx.open()) { qDebug() << "DB connection creation error!"; } } return cnx; } } And the only create on instance of this class and pass the pointer to each class which need connection to DB.

@Christian-Ehrlicher Hm ok... That's not what I wanted to hear :D Thank you anyway. I think, I will subclass QSqlQueryModel then and write functions to make the model writable...

@user4592357 said in cannot execute queries on a database: if (!query.exec("CREATE TABLE artist (ID integer primary key Name varchar)")) { qDebug() << query.lastError().text(); return false; } should be: if (!query.exec("CREATE TABLE artist (ID integer primary key, Name varchar)")) { qDebug() << query.lastError().text(); return false; }

From the looks of it, you have to re-create the models when you change these settings.

What do you mean by modify the model ? i mean updating model , like a search window that needs to update model every time user change input. You can see how to handle QtSQL models and views in the QtSQL modules examples. i saw it, and figure out some of examples. but i need to read more about MVC in qt. thanks you.

@mrjj I have moved forward from calling my saved dates to receive the following: Read Value: [object Object],[object Object],[object Object],[object Object],[object Object],[object Object] for key: dates (one for each date saved) when adding if(success) { console.log(JSON.stringify(value)) } I can also read the saved dates in the format of: [{"date":"2018-10-01T21:17:00.926"},{"date":"2018-10-02T12:00:00.000"},{"date":"2018-10-03T12:00:00.000"},{"date":"2018-10-06T12:00:00.000"},{"date":"2018-10-07T12:00:00.000"},{"date":"2018-10-08T12:00:00.000"}] now how would I determine these dates are saved in my calendar to add the marker? I have tried adding a property bool to the marker so the read value equals isMarked = true yet this either marks every date on the calendar or none at all depending on how I am working this?!? How would I convert the JSON string to individual date reads?

I have add C:\mysql\mysql-5.7.21-winx64\lib into path variable. but don't work!

@mrjj Many thanks mrjj for your answer. I'll make more researches about SQLite and Taglib.

@tskardal said in How do you persist and update your models?: I'm thinking that the goal is having "plain" models that are not QObjects. That's a quite normal thing to do. Let the Qt model be just an intermediary between actual data model/tree and the GUI. If your implementation works, then it's OK I guess. I'm not sure if there any actual question to answer here :-)

@aliks-os http://www.qtrpt.tk I cannot connect to this site...

Hi, Are you aware of the implications of moving from MySQL to SQLite ? One of which is: you are using a relative path for your SQLite database which won't work if your users install your application in e.g. Program Files as it's a read-only location.

Hi, To add to @dream_captain, in case of an error, at least print the error string from the query so you know what went wrong.

The most compatible with qt is GE Predix (https://www.predix.io/) - https://github.com/IndeemaSoftware/QPredix

@Kushan Or you can use resizeColumnsToContents() method for the same.

@abforce said in Looking for the best multithreading patterns for database access: For this purpose can I employ a callback pattern? You can simply use signals/slots across threads

@SGaist Thank you for your answer!

@Lasith You should open the database only once. Currently you do it each time button is pressed.

Hi, There's no need for any global objects all the more if you only have one active connection for your application but it's also valid if you are managing multiple connections. The QSqlDatabase class already provides everything you need. Like written in the documentation, if you are only using one connection, don't give it a name, it will become the default connection and all the SQL related classes will use it by default. If you have several connections, it's easy to retrieve the one you are interested in by using QSqlDatabase::database. On a side note, you should properly test the outcome of your open call. Right now it could be failing and you don't care about that possibility.

@mostefa said in connecting to database when a form loads using signals and slots: I think that this post is duplicate Strictly speaking it isn't, although it's quite similar.

@mostefa Thanx mate

@spektro37 Well its used with all QWidgets so would make sense. Its something to be aware of when creating GUI and also the little note that any QWidget that are not given a owner/parent, will become a window. That can be surprised when coming from other frameworks. Say you make a new label QLabel *lab= new QLabel(); Since its given no parent, it will become a window. That was pretty surprising to me first time as i wanted to insert it into the main window. So its good to know about.

@DoughBoy The following SQL, with the Chinook test database open will create a new file in the same directory named 'out.sqlite' holding all of the album information for artist 51 with the original table layout. A Qt model is totally unnecessary. Just run the query and it will create your file. From there you can compress it and ship it. ATTACH DATABASE 'out.sqlite' AS outdb; CREATE TABLE outdb.album AS SELECT * from album WHERE ArtistId = 51; DETACH DATABASE outdb; It does use SQLite specific sql. Note especially that the ATTACH DATABASE and DETACH DATABASE are sql to be sent to the database just like the CREATE TABLE.. BTW, I have never done this using Qt, only in batch files, but I see no reason for it not to work both ways. Mike

// QSpinBox* mySpinBox; //QSqlQueryModel *model; // int rowIndex,colIndex; QObject::connect(mySpinBox, static_cast<void (QSpinBox::*)(int)>(&QSpinBox::valueChanged),[model,rowIndex,colIndex](int val)->void{ model->setValue(model->index(rowIndex,colIndex),val); });

@VRonin Thank you for reply, but my problem is the load image from database, please see my another question: QT 5.8 image from database error

@mrjj Thanks a lot Brother :) My Problem Solved!

Have you tryed axcontainer? Please try this. It this application works for you I can help you. http://www.denisgottardello.it/ADOTest/index.php

hi You can use http://doc.qt.io/qt-5/qdatawidgetmapper.html to insert data to label. It can not be directly tied to a model.

@hskoglund Thank You So much man My Problem Solved!

thanks @veryqtperson . I will try to implement it

For a beginner I have found Youtube tutorials from VoidRealms very helpful. For example this tutorial is about editing in a database table: https://www.youtube.com/watch?v=LkbfNoZrTBQ&list=PL2D1942A4688E9D63&index=56 (C++ Qt 56 - QSqlTableModel )

@Qinyx Good work.