How to use an Object of type QSqlTableModel in another function of the same class?

mooswitz

I tried to reply here but akismet is constantly flagging my reply as spam. Therefore I posted my reply to Pastebin:
https://pastebin.com/e2SVXZVb

Here I made an error. It was meant so say:
"In any source-file where a database connection is needed I can now use the class DatabaseManager to call QSqlDatabase DB_Connection = DatabaseManager::instance();
So I can later check for isOpen(). That seems a lot better to me."

JonB

@mooswitz
I don't know why you are getting "spam". I wouldn't normally look at pastebin or anything else external.

You now have

static QSqlDatabase db;

as a member variable. Which goes against what the docs tell you (not) to do. Get rid of a member variable and use QSqlDatabase::database() static function per the docs.

mooswitz

@JonB

I got it now. I germany one would say "I was standing on the hose" I think it's best translated as: "I was drawing a blank" :D

I don't know what exactly was that hard for me to understand that but now I got it. So if i set the Database once in any source file by executing this:

    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    db.setHostName(DBHOSTNAME);
    db.setDatabaseName(DBNAME);
    db.setUserName(DBUSERNAME);
    db.setPassword(DBPASSWORD);

then I can get that connection always and everywhere inside my project with simply calling

QSqlDatabase db = QSqlDatabase::database();

how can I make it work with several database connections? Let's say I have two different databases...

Would i then add them like so: ?

    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL","MyDB1");
    db.setHostName(DBHOSTNAME);
    db.setDatabaseName(DBNAME);
    db.setUserName(DBUSERNAME);
    db.setPassword(DBPASSWORD);

    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL","MyDB2");
    db.setHostName(DBHOSTNAME);
    db.setDatabaseName(DBNAME);
    db.setUserName(DBUSERNAME);
    db.setPassword(DBPASSWORD);

JonB

@mooswitz
Look at the docs!
QSqlDatabase QSqlDatabase::database(const QString &connectionName = QLatin1StringView(defaultConnection), bool open = true)

Returns the database connection called connectionName.

artwaw

@mooswitz More or less yes. But try first with one connection and see how it works, don't be afraid to recall it everywhere you might need to. I'd wager it will work without a snag.

SGaist

@mooswitz in addition to what my fellows wrote: the SQL related classes you use offer error methods that allow you to learn what went wrong. Using them will help you more than just printing "something wrong happened".

artwaw

@SGaist Great suggestion, I forgot to mention them.
You can #include <QSqlError> and then qDebug() << relevant db and QSqlQuery (and others) .error() or .lastError().text() and similar.

mooswitz

@SGaist @artwaw

Thank you both for your advices but I indeed used the .lastError() and related functions already. I did'nt mention them in my first posts because initially QSqlDatabase was'nt my problem. Although I made mistakes that I now have corrected. It's working perfect now.

My concern was: how can I use QSqlTableModel to trigger .submitAll(); via a button. But since I use a member variable it works.
I wonder if there is a similar approach to it like with QSqlDatabase::database(); now that I know how to use that it's super nice.

But I think that my initial problem got solved by correcting the database connection. So thanks. I consider this thread as solved.

Greetz, mooswitz

SGaist

@mooswitz said in How to use an Object of type QSqlTableModel in another function of the same class?:

My concern was: how can I use QSqlTableModel to trigger .submitAll(); via a button. But since I use a member variable it works.
I wonder if there is a similar approach to it like with QSqlDatabase::database(); now that I know how to use that it's super nice.

Don't, that would be unclean. It is not a design pattern that would fit that use case.

mooswitz

@SGaist said in How to use an Object of type QSqlTableModel in another function of the same class?:

Don't, that would be unclean. It is not a design pattern that would fit that use case.

Okay. So What would be the better approach? I have taken the time now to figure out what would work better instead... so first: Why is there the "submitAll()" method, if I should'nt use it with a Button or sth. similar to trigger it? Or did you mean that I should not use the member variable for that?

What I want to do is the following: You (as a user) get presented with a TableView, showing some Data from a mariadb. This Data (in my case userdata) can be edited here. I do not want it to update directly after change. So that's Why I want a button to trigger that. Regarding the option to use QSqlTableModel for that - what is then the better option to trigger an Insert to the db with the Data loaded with the TableModel?

SGaist

The unclean part was about trying to have a global QSqlTableModel in a similar fashion to QSqlDatabase.
For the rest, you did thing correctly. ~~You could even simplify a bit by connecting the button directly to the submitAll function.~~ Bad suggestion, you'd lose error handling.

mooswitz

Okay. Thanks a lot!

How would I do that? I mean: connecting the button directly to the function?

SGaist

@mooswitz sorry, that was a bad suggestion, you would lose the error handling check.