[PyQt] QRelationalTableModel usage question

[Ricardo Araoz]

Hi,
     I'm looking at an app from a tutorial which instantiates a Main 
window with two QTableViews in a master-detail relationship. You can see 
the code for adding a master record below, when you add a master record 
you MUST (requirement) add an initial detail record. This code will not 
work properly.
The code starts a transaction, then adds an empty master record, then 
queries the MAX() id from the master table and increments it by one, 
simulating the PRIMARY KEY AUTOINCREMENT action of the database in the 
id field, it then inserts a detail record and sets a relation with the 
master table through the masterid field.
The code will work except when adding a master record after you've 
deleted a master record, in which case the MAX(id) + 1  will not be the 
next id (as the original maximum id has been deleted), and from then on 
the initial detail records created will not be linked to the proper 
master id.
I've tried to find out the proper id value by checking the 
masterModel.data() value for the id, but it returns a QPyNullVariant, 
tried a masterModel.submitAll() with the same result, tried querying the 
table but it seems the record will not be seen until you commit the 
transaction, but I cannot commit the transaction if the detail record 
has not been created and correctly populated (it would be as not using 
transactions and there will be a space of time in which the detail 
record is not linked to it's proper master record).
My question is, how can I get the proper id value?

     def addMaster(self):
         db = self.masterModel.database()
         row = (self.masterView.currentIndex().row()
                if self.masterView.currentIndex().isValid() else 0)

         db.transaction()
         self.masterModel.insertRow(row)
         index = self.masterModel.index(row, NAME)
         self.masterView.setCurrentIndex(index)

         mastertid = 1
         query = QSqlQuery()
         query.exec_("SELECT MAX(id) FROM master")
         if query.next():
             masterid = query.value(0) + 1
         query.prepare("INSERT INTO detail (masterid, date, actionid) "
                       "VALUES (:masterid, :date, :actionid)")
         query.bindValue(":masterid", masterid)
         query.bindValue(":date", QDate.currentDate())
         query.bindValue(":actionid", SOMEACTION)
         query.exec_()
         db.commit()
         self.masterView.edit(index)