Extending Wagtail Streamfields In An Inherited Class

I have a abstract class that have ha StreamField in it. I also have a class CustomPage that inherits from BasePage. I want CustomPage to add a new StructBlock to content. How do i

Solution 1:

The StreamField definition can't be 'extended' directly in this way, but with a bit of re-shuffling you can define a new StreamField that re-uses the same block list:

COMMON_BLOCKS = [
    ('ad', ...),
    ('text', ...),
    ('img', ...),
]

class BasePage(Page):
    content = StreamField(COMMON_BLOCKS)
    ...

class CustomPage(BasePage):
    content = StreamField(COMMON_BLOCKS + [
        ('custom_block', ...),
    ])

Or using inheritance on StreamBlock (which you might consider a bit neater than concatenating lists:

class CommonStreamBlock(StreamBlock):
    ad = ...
    text = ...
    img = ...

class CustomStreamBlock(CommonStreamBlock):
    custom_block = ...

class BasePage(Page):
    content = StreamField(CommonStreamBlock())
    ...

class CustomPage(BasePage):
    content = StreamField(CustomStreamBlock())

Also, note that this is only possible since Django 1.10 - older versions of Django don't allow overriding fields of an abstract superclass.

Solution 2:

I found one more solution beside @gasman solutions.

It uses the deconstruct method in Stream field to get all the blocks from BasePage StreamField. It uses those blocks when creating the content StreamField in the CustomPage.

I will use this one for now but i think @gasman last solution is the most beautiful solution.

class BasePage(Page):
    content = StreamField([
        ('ad', ...),
        ('text', ...),
        ('img', ...),
    ])
    content_panels = Page.content_panels + [
        StreamFieldPanel('content'),
    ]
    @staticmethod
    def get_content_blocks():
        return list(BasePage.content.field.deconstruct()[2][0])

    class Meta:
        abstract = True

class CustomPage(BasePage):
    content = StreamField(BasePage.get_content_blocks() +
        [
            ('custom_block', ....),
        ]
    )