Include custom form media in templates

[andreynovikov]

Problem

When custom import/export forms contain complex widgets with linked media it is not added to output.

Solution

Added standard form.media to templates.

Acceptance Criteria

This fix does not require tests and documentation changes.

[coveralls]

Coverage decreased (-0.08%) to 95.519% when pulling fc7fe0a on andreynovikov:form-media-fix into 3cf5e3f on django-import-export:master.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[andrewgy8]

Hey @andreynovikov . Thanks for the PR. When you say

custom import/export forms contain complex widgets

Can you give an example of this and some screeshots? Also how does this effect current/standard behavior?

[ababic]

I've also ran into this problem. @andrewgy8 you can recreate this in the test app by updating tests.core.forms.AuthorFormMixin like so:

from django.contrib import admin
from django.contrib.admin.widgets import AutocompleteSelect


class AuthorFormMixin(forms.Form):
    author = forms.ModelChoiceField(
        queryset=Author.objects.all(),
        widget=AutocompleteSelect(Author.objects.all(), admin_site=admin.site, using=Author.objects.all().db)
    )

If the form media is loaded correctly, the field should use the nice autocomplete widget you get in an edit form when you use autocomplete_fields on a ModelAdmin instance. When it isn't, you see a standard select field without any options (because the JS to load them isn't included).

[andrewgy8]

Hey! Is this safe to be merged to master?

[matthewhegarty]

I would be OK with including this but I would like to understand exactly how it works. Can anyone supply steps to reproduce / screenshots / or a more detailed explanation of what's going on. I read Andy's comment but I'm still not clear on what the nature of this change is.

[ababic]

@matthewhegarty In a nutshell, Django has a mechanism that allows form widgets to register additional JS and CSS so that they can function properly. However, if you do not render form.media (a collation of all the JS and CSS required for all fields/widgets used for that form), that JS and CSS is unavailable in the front-end, and widgets do not look or function correctly.

[matthewhegarty]

@ababic Andy - thanks for the explanation, I understand what's going on now. I was able to reproduce the issue in the v3 codebase as follows (adapted from Andy's post):

forms.py

class AuthorFormMixin(forms.Form):
    author = forms.ModelChoiceField(
        queryset=Author.objects.all(),
        widget=AutocompleteSelect(Book._meta.get_field('author'), admin.site)
    )

#...

class CustomExportForm(AuthorFormMixin, ExportForm):
    """Customized ExportForm, with author field required"""
    pass

admin.py

class AuthorAdmin(ImportMixin, admin.ModelAdmin):
    search_fields = ['name']


class CustomBookAdmin(BookAdmin):
    """BookAdmin with custom import forms"""
    autocomplete_fields = ['author']

# ...

    def get_export_form(self):
        return CustomExportForm

(then add the PR changes to import.html & export.html)

This results in the correct autocomplete widget being show, with 'author' values being dynamically populated.

[matthewhegarty]

I've updated this PR with merges from v3.
I have tested this change manually in the admin site.

[matthewhegarty]

Thank you @andreynovikov and @ababic

[ababic]

Thanks @matthewhegarty! Happy Easter to you :)