Pickling error when auto_append = False

[obscode]

Using this awesome widget in a form. I want to disable the auto_append feature. I followed the instructions in the README file and used the form's updateWidgets() function to set the widget's auto_append = False.

If I fill out the data with a single row (i.e., DO NOT add or subtract), and I get an error:
[...]
PicklingError: Can't pickle <class 'z3c.form.interfaces.NO_VALUE'>: it's not the same object as z3c.form.interfaces.NO_VALUE

This occurs because when rendering the HTML for the widget, two rows are made: the input row and the template for the next added row (the 'TT' row). But the hidden count variable is set to 2 instead of 1 and this causes (I'm guessing) the NO_VALUE problem. Interestingly, if I add a row, then subtract it, the count goes down to 1 and the form submits correctly. I guess the JS logic fixes the problem in this case.

Debugging a bit, it seems that the function datagridfield.DataGridField.updateWidgets() will always add the "AA" and "TT" widgets because this is run before auto_append can be set to False (it is run as part of the super class' updateWidgets()). So there are always at least 3 widgets. But in the page template for the widget (datagridfield_input.pt) there is a conditional that will prevent the 'AA' widget from rendering if auto_append is False (which it is by the time the page template is rendered). So there's a timing with when self.auto_append is accessed giving inconsistent values.

I fixed the issue for this specific case by simply hacking datagridfield.py and hard-coding the default auto_append=False so everything is consistent from the get-go. But that's not a good solution. Not sure what is.

[cekk]

+1 i've found the same error this week.
And i hacked the form in the same way, but i'd like to fix it in a safe way.

Any ideas?

[luca-bellenghi]

Same error here with the last version in Plone5.2/python3.
Hardcoding auto_append to False is not working

[thet]

That problem haunted me too today.
What I found out:

• The collective.z3cform.datagridfield.datagridfield.DataGridField is a instance of z3c.form.widget.MultiWidget.
• The extract method in the MultiWidget expects a counter variable in request.form which defines how much different rows are submitted.
• The rows must be properly named, so that self.getWidget(idx) returns a valid row. Otherwose it will return a <NO_VALUE> object. The comparison against the NO_VALUE class then fails, as we have seen in the PicklingError, for whatever reason. Normally, no one should be able to import the NO_VALUE class from z3c.form.interfaces. However, I guess this is a bug in z3c.form. With a pdb in the extract method, try to self.getWidget(0) and if you submitted at least one row you should get a DataGridFieldObject or the like back. Try to self.getWidget("TT").value, that should be the template row. And a self.getWidget("abc").value will return <NO_VALUE>.
• The proper fix is to correctly calculate the count.

This should get fixed in this PR: #106

[thet]

Should be fixed with: #106

[yurj]

It happened to me with DataGridField and LinkFieldWidget.