QSqlTableModel() empty on Ubuntu but works on Windows ?

[JonB]

@R-P-H
Of how to sub-class in C++? It's just basic C++.

I see @SGaist offered this 7 years ago: https://forum.qt.io/topic/30562/example-of-subclassing-qsqltablemodel/2. You'll want something like:

// mytablemodel.h
class MyTableModel : public QSqlTableModel
{
public:
explicit MyTableModel(QObject * parent = 0, QSqlDatabase db = QSqlDatabase() ); // the same arguments as QSqlTableModel

protected:
virtual QString selectStatement() const;
};

// mytablemodel.cpp
MyTableModel::MyTableModel(QObject * parent, QSqlDatabase db) :
QSqlTableModel(parent, db)
{
// the rest of your code
}

QString MyTableModel::selectStatement() const
{
    QString ss = QSqlTableModel::selectStatement();
    qDebug() << ss;
    return ss;
}

I don't think QSqlQuery QSqlQueryModel::query() const is virtual, so you can't override it; nor is it protected, it's public, so just call it if you need to access it.

[R-P-H]

@JonB I'm not quite sure how to implement this correctly. I have a class that deals with all database related stuff. Inside that class I have a function that generates the QSqlTableModel using the code you've already seen.

Now obviously if I create another class for MyTableModel, include it and create model using MyTableModel *model = new MyTableModel(nullptr, db); instead I still get a protected function error when calling its selectStatement() member.

What would be the correct way of testing this ? Thanks.

[JonB]

@R-P-H

Inside that class I have a function that generates the QSqlTableModel

You don't want to directly create a QSqlTableModel anywhere, you want it now to create a MyTableModel. E.g if you currently have a new QSqlTableModel somewhere it now goes new MyTableModel. This is basic C++ sub-classing, I don't know whether you're confused over that.

include it and create model using MyTableModel *model = new MyTableModel(nullptr, db); instead I still get a protected function error when calling its selectStatement() member.

Assuming you've got the first bit right, you still cannot call a protected method on an instance from outside of the MyTableModel class code, that's what protected is all about. You will need something like the definition I showed you of QString MyTableModel::selectStatement() const. You can either then write another public method in MyTableModel which calls it and the outside world can go via that public method, or (as I do) override all the methods in MyTableModel which do queries, updates etc. and have them print it out. It takes a few minutes to write these override functions, but once you have them from then on it's a lot easier to see what's going on, do logging, handle any errors etc. from the QSql... classes you use.

[R-P-H]

@JonB The result of selectStatement() is " ".

[SGaist]

Would you be able to provide a small step by step guide to reproduce your test database ? Meaning the command you are currently using on your Linux machine to create the role and the database.

[R-P-H]

@SGaist Hi, I just use psql to create the database/table/user.

CREATE DATABASE my_db
    WITH 
    OWNER = postgres
    ENCODING = 'UTF8'
    TABLESPACE = pg_default
    CONNECTION LIMIT = -1;

CREATE ROLE my_user WITH
  LOGIN
  NOSUPERUSER
  INHERIT
  NOCREATEDB
  NOCREATEROLE
  NOREPLICATION
  ENCRYPTED PASSWORD 'md5hidden';

CREATE TABLE public.my_table
(
    example_column character varying COLLATE pg_catalog."default",
)

TABLESPACE pg_default;

ALTER TABLE public.my_table OWNER to postgres;

GRANT INSERT, SELECT, DELETE ON TABLE public.my_table TO my_user;

So for example:

sudo -u postgres psql -c 'one of the above blocks of code'

So here my_db is the database name, my_user is the role I'm using to access the table and my_table is the table name.

[R-P-H]

Is there anything else I can try ?

[SGaist]

Sorry I did not had time to test the database.

One thing that you could try (I don't think it would change anything but worth a try), reorder the database setup and add your custom role and it setup both at the end.

[R-P-H]

@SGaist said in QSqlTableModel() empty on Ubuntu but works on Windows ?:

Sorry I did not had time to test the database.

One thing that you could try (I don't think it would change anything but worth a try), reorder the database setup and add your custom role and it setup both at the end.

I guess I could try that but why would the error be

QSqlError("", "Unable to find table logs", "")

then ?

[SGaist]

Gut feeling: PostgreSQL namespace.

[R-P-H]

@SGaist said in QSqlTableModel() empty on Ubuntu but works on Windows ?:

Gut feeling: PostgreSQL namespace.

I had a look, but I don't quite understand how it applies to this...

[SGaist]

The database role must have access to the namespace in order to access the relation it contains.

There might be a glitch there.

[R-P-H]

@SGaist said in QSqlTableModel() empty on Ubuntu but works on Windows ?:

The database role must have access to the namespace in order to access the relation it contains.

There might be a glitch there.

Yet the same role (same exact application/code) works fine on Windows ?

[R-P-H]

Upgrading to Qt Version 5.15+ solved the issue.