QSqlRecord sets column with default value to null in query

You can use removeColumn(int) before QSqlRecord rec = model->record() and it should work. If model is associated to a view (a QTableView instance, for example), you'll be effectively hiding the samochod_id column, though.

Try this:

  // get the index of the id column
  int colId = model.fieldIndex("samochod_id");
  // remove the column from the model
  model.removeColumn(colId);

  QSqlRecord rec = model->record();

  // rec.setGenerated("samochod_id", false); /// not needed anymore
  rec.setValue("marka", ui.brandEdit->text());
  rec.setValue("poj_silnika", ui.volSpin->value());
  rec.setValue("typ_silnika", ui.engineCombo->currentText());
  rec.setValue("liczba_osob", ui.passengersSpin->value());

  bool ok = model->insertRecord(-1,rec);

I can understand why you prefer to insert records this way (avoid writing SQL manually). I think using a QSqlTableModel instance just for the purpose of inserting records is too expensive (models are complex beasts), so I prefer to use a plain QSqlQuery. With this approach it is not necessary to instantiate multiple QSqlTableModels if you need to insert records in multiple tables in a transaction, a single QSqlQuery is enough:

  QSqlDatabase::database("defaultdb").transaction();
  QSqlQuery query(QSqlDatabase::database("defaultdb"));

  query.prepare(QString("INSERT INTO table1 (field1, field2) VALUES(?,?)"));
  query.bindValue(0,aString);
  query.bindValue(1,anotherString);
  query.exec();

  // insert in another table
  query.exec(QString("INSERT INTO table2 (field1, field2) VALUES(...)");

  bool ok = QSqlDatabase::database("defaultdb").commit();
  query.finish();

  if(!ok){
      // do something
  }