tableView->setModel(model); causes SIGSEGV.

[snubben]

Can I have this function scope of db? A bit cleaner code.

QSqlDatabase db = QSqlDatabase::database();

I changed the code to use only QSqlDatabase::database(). Still crashing. By the way, I have another query that works with the database, difference is that I return the records in a QStringList. In case it is relevant.

[Christian Ehrlicher]

Iterate through the sqlquery results instead setting it to the model to see if it is still crashing. How did you build the Qt mysql plugin? Also I'm pretty sure query.exec() should not be called.

[Pl45m4]

@snubben said in tableView->setModel(model); causes SIGSEGV.:

QSqlDatabase db = QSqlDatabase::database();

I changed the code to use only QSqlDatabase::database(). Still crashing

I mentioned this because it's a cleaner solution. It wouldn't solve your crash issue anyway.

Edit:
As @Christian-Ehrlicher says above, the query.exec() + setQuery in combination with std::move is also weird.
You set execute the query, then passing a move-constructed query to the model, leaving the initial query in an undefined state.
(using the forum search function, you will find a lot of topics on this, like this one)

If I'm not mistaken setQuery will do the job for you.
Or you do it as shown in the QueryModel-Example.

[snubben]

@Christian-Ehrlicher said in tableView->setModel(model); causes SIGSEGV.:

Iterate through the sqlquery results instead setting it to the model to see if it is still crashing. How did you build the Qt mysql plugin? Also I'm pretty sure query.exec() should not be called.

The documentation for QSqlQueryModel says

Resets the model and sets the data provider to be the given query. Note that the query must be active and must not be isForwardOnly().

Apparently query.exec() makes it active:

    qDebug() << "Is active:" << query.isActive();
    query.exec();
    qDebug() << "Is active:" << query.isActive();

Is active: false
Is active: true

I just did

    query.exec();
    while (query.next()) {
        QString field1 = query.value(0).toString();
        QString field2 = query.value(1).toString();
        qDebug() << "field1:" << field1 << ", field2:" << field2;
    }

and it works fine.

I built the mysql driver using

mkdir ~/dev/cpp/QtBuilds/build-sqldrivers
cd build-sqldrivers
qt-cmake -G Ninja ~/Qt/6.7.2/Src/qtbase/src/plugins/sqldrivers -DCMAKE_INSTALL_PREFIX="~/Qt/6.7.2/Src" -DMySQL_INCLUDE_DIR="/usr/include/mysql" -DMySQL_LIBRARY="/usr/lib/libmysqlclient.so"
cmake --build .
cmake --install .

and it didn't report errors.
In my application I have this so it finds the driver. This is the folder that "cmake --install ." installed to.

QCoreApplication::addLibraryPath("/home/username/Qt/6.7.2/Src/lib/qt6/plugins");

@Christian-Ehrlicher said in tableView->setModel(model); causes SIGSEGV.:

Or you do it as shown in the QueryModel-Example.

Yes, a simple QString query like that works. But I need to search based on search criterias, thus the dynamic SQL. I haven't found that it is possible to bind values to the model.

[snubben]

@Pl45m4 said in tableView->setModel(model); causes SIGSEGV.:

@snubben said in tableView->setModel(model); causes SIGSEGV.:

QSqlDatabase db = QSqlDatabase::database();

I changed the code to use only QSqlDatabase::database(). Still crashing

I mentioned this because it's a cleaner solution. It wouldn't solve your crash issue anyway.

Edit:
As @Christian-Ehrlicher says above, the query.exec() + setQuery in combination with std::move is also weird.
You set execute the query, then passing a move-constructed query to the model, leaving the initial query in an undefined state.
(using the forum search function, you will find a lot of topics on this, like this one)

If I'm not mistaken setQuery will do the job for you.
Or you do it as shown in the QueryModel-Example.

If I use

model->setQuery("select * from products");

it works. It shows the data. But I cannot bind variables then. Again, I am 100% new to C++/Qt so might miss some fundamental principle on how to achieve this.

I see from the thread you linked that the query.exec(), std::move is also used there.

[JonB]

@snubben said in tableView->setModel(model); causes SIGSEGV.:

it works. It shows the data.

So now per your earlier debug information try the actual query which seems to be executed with your bindings:

SELECT field1, field2, prodCount, field3, prod_date  FROM products WHERE 1 = 1 ORDER BY prod_date DESC;

How does that fare?

If that works standalone, next try that as a literal for your model, this way:

QSqlQueryModel* model = new QSqlQueryModel(this);
model->setQuery("SELECT field1, field2, prodCount, field3, prod_date  FROM products WHERE 1 = 1 ORDER BY prod_date DESC;");

How does that fare?

[snubben]

@JonB said in tableView->setModel(model); causes SIGSEGV.:

@snubben said in tableView->setModel(model); causes SIGSEGV.:

it works. It shows the data.

So now per your earlier debug information try the actual query which seems to be executed with your bindings:

SELECT field1, field2, prodCount, field3, prod_date  FROM products WHERE 1 = 1 ORDER BY prod_date DESC;

How does that fare?

If that works standalone, next try that as a literal for your model, this way:

QSqlQueryModel* model = new QSqlQueryModel(this);
model->setQuery("SELECT field1, field2, prodCount, field3, prod_date  FROM products WHERE 1 = 1 ORDER BY prod_date DESC;");

How does that fare?

Yes, all those work! How to I apply search criterias if I use a QString query?

[snubben]

So I debugged some more and if I understand correctly it seg faults in qsql_mysql.cpp at

bool QMYSQLResult::fetch(int i)
{
    Q_D(QMYSQLResult);
    if (!driver())
        return false;
    if (isForwardOnly()) { // fake a forward seek
        if (at() < i) {
            int x = i - at();
            while (--x && fetchNext()) {};
            return fetchNext();
        } else {
            return false;
        }
    }
    if (at() == i)
        return true;
    if (d->preparedQuery) {
        mysql_stmt_data_seek(d->stmt, i);

        int nRC = mysql_stmt_fetch(d->stmt); <<<< HERE SEG FAULT
        if (nRC) {
            if (nRC == 1 || nRC == MYSQL_DATA_TRUNCATED)
                setLastError(qMakeStmtError(QCoreApplication::translate("QMYSQLResult",
                         "Unable to fetch data"), QSqlError::StatementError, d->stmt));
            return false;
        }
    } else {
        mysql_data_seek(d->result, i);
        d->row = mysql_fetch_row(d->result);
        if (!d->row)
            return false;
    }

    setAt(i);
    return true;
}

d pointer has the following information:

	*d	@0x5555557afe10	QMYSQLResultPrivate
		[QSqlResultPrivate]	<not accessible>	QSqlResultPrivate
		fields	<5 items>	QList<QMYSQLResultPrivate::QMyField>
			[0]	@0x55555573e930	QMYSQLResultPrivate::QMyField
				bufLength	401	ulong
				*myField	@0x555555929d88	MYSQL_FIELD
					catalog	"def"	char *
					catalog_length	3	unsigned int
					charsetnr	45	unsigned int
					db	"database_name"	char *
					db_length	9	unsigned int
					decimals	0	unsigned int
					def	0x0	char *
					def_length	0	unsigned int
					extension	0x0	void *
					flags	20483	unsigned int
					length	400	unsigned long
					max_length	0	unsigned long
					name	"field1"	char *
					name_length	7	unsigned int
					org_name	"field1"	char *
					org_name_length	7	unsigned int
					org_table	"products"	char *
					org_table_length	11	unsigned int
					table	"products"	char *
					table_length	11	unsigned int
					type	MYSQL_TYPE_VAR_STRING (253)	enum_field_types
				nullIndicator	0	my_bool
				outField	""	char *
				type	@0x55555573e940	QMetaType
			[1]	@0x55555573e958	QMYSQLResultPrivate::QMyField
				bufLength	401	ulong
				*myField	@0x555555929e08	MYSQL_FIELD
					catalog	"def"	char *
					catalog_length	3	unsigned int
					charsetnr	45	unsigned int
					db	"database_name"	char *
					db_length	9	unsigned int
					decimals	0	unsigned int
					def	0x0	char *
					def_length	0	unsigned int
					extension	0x0	void *
					flags	4097	unsigned int
					length	400	unsigned long
					max_length	0	unsigned long
					name	"name"	char *
					name_length	4	unsigned int
					org_name	"name"	char *
					org_name_length	4	unsigned int
					org_table	"products"	char *
					org_table_length	11	unsigned int
					table	"products"	char *
					table_length	11	unsigned int
					type	MYSQL_TYPE_VAR_STRING (253)	enum_field_types
				nullIndicator	0	my_bool
				outField	""	char *
				type	@0x55555573e968	QMetaType
			[2]	@0x55555573e980	QMYSQLResultPrivate::QMyField
				bufLength	4	ulong
				*myField	@0x555555929e88	MYSQL_FIELD
					catalog	"def"	char *
					catalog_length	3	unsigned int
					charsetnr	63	unsigned int
					db	"database_name"	char *
					db_length	9	unsigned int
					decimals	0	unsigned int
					def	0x0	char *
					def_length	0	unsigned int
					extension	0x0	void *
					flags	36865	unsigned int
					length	11	unsigned long
					max_length	0	unsigned long
					name	"prodCount"	char *
					name_length	5	unsigned int
					org_name	"prodCount"	char *
					org_name_length	10	unsigned int
					org_table	"products"	char *
					org_table_length	11	unsigned int
					table	"products"	char *
					table_length	11	unsigned int
					type	MYSQL_TYPE_LONG (3)	enum_field_types
				nullIndicator	0	my_bool
				outField	""	char *
				type	@0x55555573e990	QMetaType
			[3]	@0x55555573e9a8	QMYSQLResultPrivate::QMyField
				bufLength	401	ulong
				*myField	@0x555555929f08	MYSQL_FIELD
					catalog	"def"	char *
					catalog_length	3	unsigned int
					charsetnr	45	unsigned int
					db	"database_name"	char *
					db_length	9	unsigned int
					decimals	0	unsigned int
					def	0x0	char *
					def_length	0	unsigned int
					extension	0x0	void *
					flags	4097	unsigned int
					length	400	unsigned long
					max_length	0	unsigned long
					name	"field3"	char *
					name_length	4	unsigned int
					org_name	"field3"	char *
					org_name_length	17	unsigned int
					org_table	"products"	char *
					org_table_length	11	unsigned int
					table	"products"	char *
					table_length	11	unsigned int
					type	MYSQL_TYPE_VAR_STRING (253)	enum_field_types
				nullIndicator	0	my_bool
				outField	""	char *
				type	@0x55555573e9b8	QMetaType
			[4]	@0x55555573e9d0	QMYSQLResultPrivate::QMyField
				bufLength	40	ulong
				*myField	@0x555555929f88	MYSQL_FIELD
					catalog	"def"	char *
					catalog_length	3	unsigned int
					charsetnr	63	unsigned int
					db	"database_name"	char *
					db_length	9	unsigned int
					decimals	0	unsigned int
					def	0x0	char *
					def_length	0	unsigned int
					extension	0x0	void *
					flags	128	unsigned int
					length	10	unsigned long
					max_length	0	unsigned long
					name	"dateMin"	char *
					name_length	8	unsigned int
					org_name	"dateMin"	char *
					org_name_length	8	unsigned int
					org_table	"products"	char *
					org_table_length	11	unsigned int
					table	"products"	char *
					table_length	11	unsigned int
					type	MYSQL_TYPE_DATE (10)	enum_field_types
				nullIndicator	0	my_bool
				outField	""	char *
				type	@0x55555573e9e0	QMetaType
		hasBlobs	false	bool
		*inBinds	@0x5555557ce380	MYSQL_BIND
			buffer	0x5555556f1d30	void *
			buffer_length	401	unsigned long
			buffer_type	MYSQL_TYPE_STRING (254)	enum_field_types
			error	0x0	my_bool *
			error_value	0	my_bool
			extension	0x0	void *
			fetch_result	0x0	void (st_mysql_bind *, MYSQL_FIELD *, unsigned char * *) *
			flags	0	unsigned int
			is_null	""	my_bool *
			is_null_value	0	my_bool
			is_unsigned	0	my_bool
			*length	401	unsigned long
			length_value	0	unsigned long
			long_data_used	0	my_bool
			offset	0	unsigned long
			pack_length	0	unsigned int
			skip_result	0x0	void (st_mysql_bind *, MYSQL_FIELD *, unsigned char * *) *
			store_param_func	0x0	void (NET *, st_mysql_bind *) *
			u	@0x5555557ce3a0	union {...}
				indicator	0x0	char *
				row_ptr	0x0	unsigned char *
		*meta	@0x5555556eedf0	MYSQL_RES
			current_field	0	unsigned int
			current_row	0	MYSQL_ROW
			data	0x0	MYSQL_DATA *
			data_cursor	0x0	MYSQL_ROWS *
			eof	1	my_bool
			field_alloc	@0x5555556eee18	MA_MEM_ROOT
			field_count	5	unsigned int
			*fields	@0x555555929d88	MYSQL_FIELD
			handle	0x0	MYSQL *
			is_ps	0	my_bool
			lengths	0x0	unsigned long *
			row	0	MYSQL_ROW
			row_count	0	unsigned long long
		outBinds	0x0	MYSQL_BIND *
		preparedQuery	true	bool
		result	0x0	MYSQL_RES *
		row	0	MYSQL_ROW
		rowsAffected	-1	int
		*stmt	@0x5555556c81a0	MYSQL_STMT
			array_size	0	unsigned int
			*bind	@0x55555592a198	MYSQL_BIND
			bind_param_done	0	my_bool
			bind_result_done	1	my_bool
			cursor_exists	0	my_bool
			default_rset_handler	0x7ffff0cf5880 <mysql_next_result+224>	mysql_stmt_use_or_store_func
			execute_count	1	unsigned int
			extension	0x5555556a9700	void *
			fetch_row_func	140737233504192	mysql_stmt_fetch_row_func
			field_count	5	unsigned int
			*fields	@0x555555929d88	MYSQL_FIELD
			flags	0	unsigned long
			last_errno	0	unsigned int
			last_error	"\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000..."	char[513] of length 513
			list	@0x5555556c84c0	LIST
			mem_root	@0x5555556c81a0	MA_MEM_ROOT
			*mysql	@0x5555556a8280	MYSQL
			param_callback	0	ps_param_callback
			param_count	0	unsigned int
			params	0x0	MYSQL_BIND *
			prebind_params	0	unsigned int
			prefetch_rows	1	unsigned long
			request_buffer	0x0	unsigned char *
			request_length	0	size_t
			result	@0x5555556c8220	MYSQL_DATA
			result_callback	0	ps_result_callback
			*result_cursor	@0x55555590fa68	MYSQL_ROWS
			row_size	0	size_t
			send_types_to_server	'\0'	0	0x00	unsigned char
			sqlstate	"00000\000"	char[6] of length 6
			state	MYSQL_STMT_USER_FETCHING (5)	enum_mysqlnd_stmt_state
			stmt_id	18	unsigned long
			update_max_length	0	my_bool
			upsert_status	@0x5555556c8290	mysql_upsert_status
			user_data	0x0	void *

I have anonymized the SQL and database information, therefore the field name lengths do not match.

[Christian Ehrlicher]

You should really strip this down to a minimal, compileable example. Simply open a db connection, create and fill a table and set the query to the model. Modify it to your use case until it is crashing or you can see what you are doing wrong.

[JonB]

@snubben
As @Christian-Ehrlicher says.

Given that you say

QSqlQueryModel* model = new QSqlQueryModel(this);
model->setQuery("SELECT field1, field2, prodCount, field3, prod_date  FROM products WHERE 1 = 1 ORDER BY prod_date DESC;");

does work I am not sure where your actual example differs significantly from this. Try it now the way you do it as

QSqlQueryModel* model = new QSqlQueryModel(this);
QSqlQuery query(db);
query.prepare("SELECT field1, field2, prodCount, field3, prod_date  FROM products WHERE 1 = 1 ORDER BY prod_date DESC;");
model->setQuery(query);

I have not included your std::move() not your query.exec();. Only add those in if it does not work as is. See where you get to. If you get that working I'm sure you can then start introducing parameter bindings.

At some point you ought get rid of that QSqlDatabase db class member variable. Per the docs you should be using the static QSqlDatabase QSqlDatabase::database() for that instead. I don't know whether it might be relevant here, probably not but you never know.

[snubben]

It works!

QSqlTableModel* model = new QSqlTableModel(this);

Using this it works. I must read more about QSqlQueryModel and why it didn't work in this situation.
Thank you all!

[JonB]

@snubben said in tableView->setModel(model); causes SIGSEGV.:

Using this it works.

@Christian-Ehrlicher
OP reports that QSqlTableModel works for his QTableView but not QSqlQueryModel. I wonder why? QTV only requires a QAbstractItemModel, QSqlTableModel inherits from QSqlQueryModel, why should the latter not work?

The model for QTV must not be forward-only. Is QSqlQueryModel perhaps automatically forward-only, is that an issue?

UPDATE
Non-issue, see further posts below.

[snubben]

This works too!

QSqlQueryModel* model = new QSqlQueryModel(this);

I feel like a complete moron. I had to check git and in an other function where I get strings for a QComboBox I had

    if (!QSqlDatabase::database().open()) {
        qCritical() << "Database connection failed:" << QSqlDatabase::database().lastError().text();
        //emit errorOccurred(db.lastError().text());
        return result;
    }

which should have of course been

if (!QSqlDatabase::database().isOpen()) {

and this I changed without even reflecting upon it.
A lot I need to learn to properly find the erring location with Qt Creator. Once again, thanks guys & girls!

[JonB]

@snubben said in tableView->setModel(model); causes SIGSEGV.:

This works too!

QSqlQueryModel* model = new QSqlQueryModel(this);

Huh? That is what you started with right at the beginning:

QSqlQueryModel* model = new QSqlQueryModel(this);

That's from your first post. So if you're not saying you had to change from a QSqlQueryModel to a QSqlTableModel per your previous post --- and like I write to @Christian-Ehrlicher I don;t see why you should have to --- then I don't understand what you think you changed to make it work.

[snubben]

@JonB said in tableView->setModel(model); causes SIGSEGV.:

@snubben said in tableView->setModel(model); causes SIGSEGV.:

This works too!

QSqlQueryModel* model = new QSqlQueryModel(this);

Huh? That is what you started with right at the beginning:

QSqlQueryModel* model = new QSqlQueryModel(this);

That's from your first post. So if you're not saying you had to change from a QSqlQueryModel to a QSqlTableModel per your previous post --- and like I write to @Christian-Ehrlicher I don;t see why you should have to --- then I don't understand what you think you changed to make it work.

In the previous post I explained that I erroneously called QSqlDatabase::database().open() twice!

[JonB]

@snubben
OK. Hopefully the moral for you is this is why we (usually) insist on people pasting a complete, minimal example of their code before spending a lot of time on fragments.

[snubben]

@JonB said in tableView->setModel(model); causes SIGSEGV.:

@snubben
OK. Hopefully the moral for you is this is why we (usually) insist on people pasting a complete, minimal example of their code before spending a lot of time on fragments.

OK, I will do that the next time, thanks!

[Pl45m4]

@snubben said in tableView->setModel(model); causes SIGSEGV.:

In the previous post I explained that I erroneously called QSqlDatabase::database().open() twice!

That's why you should use QSqlDatabase::database() and not a DB member... it's less easier to make mistakes there, since database() returns the currently opened connection.

@Pl45m4 said in tableView->setModel(model); causes SIGSEGV.:

Also:

if (!db.isOpen()) {

This looks like you store your db connection as private member in DatabaseHandler.
Don't do that, it might cause undefined behavior. Better use the static QSqlDatabase::database() whenever it's needed.

I said it here :)

@JonB said in tableView->setModel(model); causes SIGSEGV.:

At some point you ought get rid of that QSqlDatabase db class member variable. Per the docs you should be using the static QSqlDatabase QSqlDatabase::database() for that instead. I don't know whether it might be relevant here, probably not but you never know.

And @JonB said it here again :)

[snubben]

Point taken! I will remove it. Thanks!