M2M HiddenInput field not returning valid list data

Using Django
1

Hi all,

I’m having trouble this morning with submission of every form of a formset with a ManyToMany hidden_input widget. When rendered, there is a valid list of primary key ints in the field ‘value’.

<input type="hidden" name="n-18-6-state_space" value="[172, 175]" id="id_n-18-6-state_space">

When submitted, it fails validation and gives form.errors: "{‘state_space’: [‘Enter a list of values.’]}

This formset instantiation works for all the normal fields:
formset = NexusBRVMFormSet(request.POST, prefix="n-" + str(question.pk))

In the past, I’ve got the M2M content manually from request.POST.lists(), but my reading of the docs makes me think that shouldn’t be needed here(?)

I note in the docs that to save M2M data I should also call formset.save_m2m(), but my problem seems upstream from this.

2

Assuming the base form is one instance of one object and the formset are all related to that specific object (perhaps an inline formset), I don’t believe the hidden form element is necessary. The many-to-many relationship is defined by the primary keys of each related table, and that information is available from the base object and each row of the related object. The save_m2m method call is only required when you do a form.save(commit=False). (In any event, this should be something easy enough to try.)

1 Like