Optional sub-StructBlock not possible

Given a declaration like:

class FeaturedArticlesBlock(blocks.StructBlock):

    heading = blocks.CharBlock(required=False)
    articles = blocks.ListBlock(blocks.PageChooserBlock())
    action = ActionBlock(required=False)

class ActionBlock(blocks.StructBlock):
    text = blocks.CharBlock()
    link = blocks.PageChooserBlock()

The action field will always be expected to be provided in the admin, even though it is unrequired.

[lacymorrow]

This seems like an important aspect of being able to use StructBlocks appropriately. Is there any timeline for scoping out work on this?

[gasman]

Hi @danni, You’re right that required has no effect on a StructBlock. Defining the semantics of ‘required-ness’ here would get a bit complicated: in your example above there’s only one valid interpretation of leaving the action blank (namely, ‘no action set’ - you’d want featured_article.action to return None), but if ActionBlock had required=False on all of its fields then it’s ambiguous whether leaving it empty means ‘no action’ (featured_article.action = None) or ‘an action which happens to be blank’ (featured_article.action = {'text': '', 'link': None}). There’s also the question of how to deal with fields that don’t have a concept of ‘being left blank’, such as ChoiceBlock dropdowns…

Django has the same thing with formsets (if you leave a form blank, does that mean ‘no item’ or ‘an empty item’?), so it’s not impossible to solve - however, perhaps the neatest solution would be for a required=False StructBlock to be initially hidden, a bit like a ListBlock that only allows one item:

(before)

(after)

That way, there’s an explicit UI state for “this StructBlock has been left unset” rather than having to infer it from whether or not its child fields have been filled in.