[PyQt] Master-detail relationship with plain QTableView tables (no SQL database)

[Mark Summerfield]

On 2010-05-20, Vadym Honcharuk wrote:
> 2010/5/9 Mark Summerfield <list at qtrac.plus.com>:
[snip]
> Thank you, Mark!
> 
> One more question in this issue is how to save data from these three
> tables with different models in one file by QDataStream module. The
> point of problem in that save method calling  from their models itself
> and if I have  three models  - every will try open same file and save
> data in series? But seems this is not too correct desicion...
> 
> With best rgards,
> -vadym

Hi Vadym,

There are many possible approaches to this.

One approach is to make just one of the models (or a new "ModelManager"
class) responsible for saving. This class would be the only one that had
a save method and would work somewhat like this:

    open the file
    for each row in the "main" model:
	write the row's data
	for each row in the "sub" model that corresponds to main data's row:
	    write the sub model row data
	    # and if there's a sub-sub model iterate over the sub-sub
	    # model's rows that correspond to the sub model's rows
	# and if there's more than one sub model, iterate over each
	# one's corresponding rows & write their data

Other approaches are equally valid. For example, you could save one file
per model which is the simplest and probably the most maintainable
approach---and the one that I personally prefer.

Nor is saving each model's data in series necessarily bad---but it does
require you to synchronize and is more risky than the other two
approaches I've mentioned.

-- 
Mark Summerfield, Qtrac Ltd, www.qtrac.eu
    C++, Python, Qt, PyQt - training and consultancy
        "Advanced Qt Programming" - ISBN 0321635906