How to access #property variable in django template [duplicate] - django

Question

I'm using Wagtail 2.0 with a custom Block that has the following code:
class LinkButtonBlock(blocks.StructBlock):
label = blocks.CharBlock()
URL = blocks.CharBlock()
styling = blocks.ChoiceBlock(
choices=[
('btn-primary', 'Primary button'),
('btn-secondary', 'Secondary button'),
('btn-success', 'Success button'),
('btn-info', 'Info button'),
('btn-warning', 'Warning button'),
('btn-error', 'Error button'),
],
default='btn-info',
)
outline = blocks.BooleanBlock(
default=False
)
#property
def css(self):
btn_class = self.styling
if self.outline is True:
btn_class = btn_class.replace('btn-', 'btn-outline-')
return btn_class
class Meta:
icon = 'link'
template = 'testapp/blocks/link_button_block.html'
If I then try to access this css "property" in my template, nothing seems to happen. Putting a print(self) as first line inside the css def also shows nothing on the console suggesting the function never even gets called.
Using the following template:
{% load wagtailcore_tags %}
<a class="btn {{ block.value.css }}" href="{{ block.value.URL }}">{{ block.value.label }}</a>
Simply yields:
<a class="btn " href="actual.url.from.instance">actual.label.from.instance</a>
Also, block.value.styling and block.value.outline on their own work just fine, so... what am I doing wrong here?

Answer 1

The thing that's tripping you up is that the value objects you get when iterating over a StreamField are not instances of StructBlock. Block objects such as StructBlock and CharBlock act as converters between different data representations; they don't hold on to the data themselves. In this respect, they work a lot like Django's form field objects; for example, Django's forms.CharField and Wagtail's CharBlock both define how to render a string as a form field, and how to retrieve a string from a form submission.
Note that CharBlock works with string objects - not instances of CharBlock. Likewise, the values returned from StructBlock are not instances of StructBlock - they are a dict-like object of type StructValue, and this is what you need to subclass to implement your css property. There's an example of doing this in the docs: http://docs.wagtail.io/en/v2.0/topics/streamfield.html#custom-value-class-for-structblock. Applied to your code, this would become:
class LinkButtonValue(blocks.StructValue):
#property
def css(self):
# Note that StructValue is a dict-like object, so `styling` and `outline`
# need to be accessed as dictionary keys
btn_class = self['styling']
if self['outline'] is True:
btn_class = btn_class.replace('btn-', 'btn-outline-')
return btn_class
class LinkButtonBlock(blocks.StructBlock):
label = blocks.CharBlock()
URL = blocks.CharBlock()
styling = blocks.ChoiceBlock(choices=[...])
outline = blocks.BooleanBlock(default=False)
class Meta:
icon = 'link'
template = 'testapp/blocks/link_button_block.html'
value_class = LinkButtonValue