MarietjeDjango/marietje/songs/admin.py

from django.contrib import admin
from django.db.models import Count
from django.urls import reverse
from django.utils.html import format_html

from .models import ReportNote, Song


class ReportNoteInline(admin.StackedInline):
    model = ReportNote
    extra = 0

class SongHasReportNoteFilter(admin.SimpleListFilter):
    title = 'report notes'
    parameter_name = 'reportnotes'

    def lookups(self, request, model_admin):
        return (
            ('yes', 'yes'),
            ('no', 'no'),
        )

    def queryset(self, request, queryset):
        queryset = queryset.annotate(num_reports=Count('reportnote'))
        if self.value() == 'yes':
            return queryset.exclude(num_reports=0)
        if self.value() == 'no':
            return queryset.filter(num_reports=0)
        return queryset


@admin.register(Song)
class SongAdmin(admin.ModelAdmin):
    list_display = ('artist', 'title', 'user_name', 'reports')
    list_display_links = ('artist', 'title')
    list_filter = (SongHasReportNoteFilter,)
    search_fields = ('artist', 'title', 'user__name')
    inlines = [ReportNoteInline]

    @staticmethod
    def reports(song):
        # num_reports is annotated by SongHasReportNoteFilter
        return song.num_reports

    @staticmethod
    def user_name(song):
        try:
            return song.user.name
        except AttributeError:
            return '<unknown>'

    @staticmethod
    def get_readonly_fields(request, obj=None):
        return [] if request.user.is_superuser else ['hash']

@admin.register(ReportNote)
class ReportNoteAdmin(admin.ModelAdmin):
    exclude = ('song',)
    list_display = ('song', 'note', 'user')
    search_fields = ('song__artist', 'song__title', 'user__name')
    readonly_fields = ('song_link',)

    @staticmethod
    def song_link(note):
        url = reverse("admin:songs_song_change", args=(note.song.id,))
        return format_html("<a href='{url}'>{song}</a>", url=url, song=note.song)

    song_link.short_description = "Song link"