@eyllanesc Thank you very much, you are right and it works now. I thought it was a function of prepare, so it would be identical.

@Lalremruata said in How to avoid Null or empty value in QLineedit of Pyqt5:

even the self.lineEdit_2 is empty.

Are you really 100% sure? I used PyQt5 and I'm pretty sure self.lineEdit_2.text() == "" would work as expected. Get rid of all your other code and behaviour and check just this in a tiny program?

@jsulm

You should rather use https://doc.qt.io/qt-5/qstring.html#isEmpty

My understanding is PyQt5's QLineEdit.text() returns a Python str rather than a C++ QString anyway. I never found using QString methods of any use in PyQt5.

Hello,

to make easy solution I just changed the databaseName when I need the other database and go back to the first databaseName when I don't need the second db :

databaseManager::databaseManager() { QDir dir; dir.setPath("./Databases"); if (!dir.exists()){ dir.mkdir("."); } db=QSqlDatabase::addDatabase("QSQLITE"); databaseName="./Databases/battery.sqlite"; db.setDatabaseName(databaseName); dbInitCheckStep(); } void databaseManager::dbInitCheckStep() { db.open(); { QSqlQuery query; qDebug()<<"query.exec()"<< query.exec("CREATE TABLE IF NOT EXISTS check_data (step TEXT, periodical_CheckOk TEXT, periodical_CheckNo TEXT,regular_CheckOk TEXT, regular_CheckNo TEXT,general_OverhaulOk TEXT, general_OverhaulNo TEXT, rtos_aft_short_storageOk TEXT, rtos_aft_short_storageNo TEXT)"); query.finish(); query.clear(); db.close(); } QSqlDatabase::removeDatabase("QSQLITE"); } QStringList databaseManager::comboListOtMat() { QStringList listCheck; db.setDatabaseName("../Software32/Databases/kardexdb.sqlite"); db.open(); { QSqlQuery query; query.exec("SELECT otnumber FROM ot_log where ottype='EQUIPMENT' and description='BATTERY' order by cast (substr(otnumber, -2) as decimal) desc, cast(substr(otnumber,1,2) as decimal) desc"); while(query.next()) { qDebug()<<query.value(0).toString(); listCheck<<query.value(0).toString(); } query.finish(); query.clear(); db.close(); } QSqlDatabase::removeDatabase("QSQLITE"); db.setDatabaseName("./Databases/battery.sqlite"); return listCheck; }

it's not beautyfull but it's easy and it's working fine ;-)

@eleventy
Ah ha! I did think it would be a good idea to go back to some simple example Qt provides, because one can be unaware that a change one has made can affect things unexpectedly!

Sounds like you now have what you were supposed to have, well done!

Yes you do, or you can make your own custom QAbstractTableModel that will return the content of your vector of records.

Yes you do. However you can use an in-memory database if you don't want to have another database in a file.

Hi, I suggest you to create a class to manage exceptions, so if you have a situation like this

if (!MyQuery.Exec("select ..")) GeneralException.raise();
if (!MyQuery.Exec("select ..")) GeneralException.raise();
if (!MyQuery.Exec("select ..")) GeneralException.raise();

if a query fails you will jump in the exception function manager.

If you want to have the list of the columns present in a sqlite database you should use the sqlite features, so
"pragma table_info(Table01)"
To have the list of the tables I think there is a similar way.

Regards.

@JonB
I'm sorry, I thought it would be helpful if people saw the entirety of the code. I didn't know which part of the code I was lacking.

Ohhh. thank you for the instruction. I'll work on the changes.

@Christian-Ehrlicher said in SQLite3 Errors: Parameter count mismatch and Unable to fetch row:

This overload is really confusion and I wonder if it should not be marked as deprecated. There were already some bugreports about this because the usage was unexpected to the users so they did an exec afterwards and screwed up the query with it.

I appreciate your discreetness, but I don't try to hide my stupidity. ;)

@SGaist

Thanks for the reply. Indeed you are wright. It is very easy actually. I just compiled qt4.8.6 for my system. Then I found the sqlite project in sqldrivers. Compiled this library for my system, copied it and it works!

Very easy. Learned again a lot!
Thank you all for the great support!

Did you already checked the bug report system to see if there was something related ?

If not, please consider opening a new report providing a minimal compilable example showing the behaviour.

What default location did you had in mind ?

That's strange, you are binding to :ID which is not available in your query.

Hi! Just to be sure I understood this correctly: You have a single DB with a humongous number of identically structured tables? Do you really believe you can store 2^128 bits / rows / tables / whatever in your database / filesystem / datacenter?

In worst case I will have to keep in RAM about 4e+38 of 16 bytes pointers

Even that is way more rows than what a SQLite table can hold (see: https://www.sqlite.org/limits.html).

@therj

It's may be too late but... better than not.

I found the problem is sqlite version i'm using is not match with the version Qt used in the core of Qt Framework.

So, I'm check the compatible of sqlite.h (3rd party) with Qt Sqlite driver to make sure it is the same version like this:

//Qt QSqlDatabase driver for Sqlite
query = db.PrepareQuery("SELECT sqlite_version()");

//Vs 3rd Party driver (included sqlite.h)
qDebug() << "sqlite3_libversion() =" << sqlite3_libversion();

there are few note to remember:

Cannot create SQLite custom functions when db object is not open. Need to call sqlite3_initialize() before call sqlite3_create_function()

If you have more questions, contact me via facebook Lã Đại Đồng. :)

That doesn't result in a system_sqlite plugin. Why don't you download a fresh copy of QT and you will see what I mean.

@stormracer
Hi,

my development pc has this amount of memory. But for other pc i can't rely on this and i will get larger data files later. Therefor i search for a solution for managing large amount of data. My idea for sql was that database systems are made for efficient data storing and searching. I choose sqlite because it doesn't need a server in the background.

Yes, somewhat, for general purpose data. Seeing you're searching for a set of particles in space (2D space?), and assuming you're wanting to mostly search and extract from the dataset not modifying it, I'd consider some sort of HDD swapped (or database backed) k-d tree. From my experience SQL databases behave rather poorly for scientific data, especially when the datasets are big. Also you could try getting a stripped down b-tree implementation (basically a database without the bells and whistles) that you can use for storage of the data and do the indexing/searching by yourself. Or the most basic approach is to work with the data as you'd do normally, but swap the dataset instead of holding it in memory (e.g. QCache comes to mind here).

PS.
Depending on how exactly you want to build the histogram you could also simply discretize the space (if I'm correct that you're working with floating point numbers for coordinates).

@mrdebug

Thank you for your response!
Are you saying my plan seems plausible? Have you done these things before or is it an educated guess ?

I'm in R&D so I can't tell you exactly what we're doing but I can tell you we're using a NXP imX6 with embedded linux and qt and the rest i have to say generalities - a device that measures something and also has user inputs how/what to measure - it's going to run a gui and a uart with data will be coming in both ways ( not at the same time- the gui will say "go" after variable inputs to start a measurement).

Then I'll need to do computing on all that data and then write results somewhere that will again, be accessed later and printed out to gui.

I am brand new to Qt but regardless it's my responsibility to get an accurate game plan and pluck away at the pieces.

I dont and won't have anyone to write me anything. I have no say in that.. such is life.

that's why - any literature, tutorials, videos that's what i'm searching for/diving into

thanks for your time, much appreciated!

@Qjay

As far as I remember, it is not possible to create indices within a create table statement in sqlite. So you have to split this into the create table and the create index statement as mentioned by @mrjj