Example validating wagtail StructBlock

wagtail_struct_block_validation.py

from django.core.exceptions import ValidationError
from django.forms.utils import ErrorList

from wagtail.wagtailcore import blocks


class MyLinkBlock(blocks.StructBlock):
    """
    Example validating StructBlock.
    """
    link = blocks.CharBlock(required=False)
    page = blocks.PageChooserBlock(required=False)

    def clean(self, value):
        result = super(MyLinkBlock, self).clean(value)
        errors = {}
        if value['link'] and value['page']:
            errors['link'] = ErrorList([
                'This should not be set when Page is selected',
            ])
        if errors:
            raise ValidationError(
                'Validation error in StructBlock',
                params=errors
            )
        return result

Fantastic! Thank you for this.

why not simply:

class ButtonBlock(blocks.StructBlock):
    """An external or internal URL."""

    anchor = blocks.CharBlock(label=_("Anchor text"), required=True)

    target_page = blocks.PageChooserBlock(
        label=_("Page"),
        required=False,
        help_text=_("If selected, this url will be used first"),
    )
    target_url = blocks.URLBlock(
        label=_("URL"),
        required=False,
        help_text=_("If added, this url will be used secondarily to the target page"),
    )

    class Meta:
        template = "core/blocks/button.html"
        icon = "fal fa-rectangle-wide"
        label = _("Button")
        value_class = LinkStructValue

    def clean(self, value):
        if not any([value["target_page"], value["target_url"]]):
            raise ValidationError(_("Target page or URL should be specified."))

        return super().clean(value)