Attempt to create a unique together constraint between Template.name and Site

dbtemplates/admin.py

@@ -1,13 +1,14 @@
 import posixpath
 from django import forms
 from django.contrib import admin
+from django.contrib.admin.widgets import FilteredSelectMultiple
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.translation import gettext_lazy as _
 from django.utils.translation import ngettext
 from django.utils.safestring import mark_safe
 
 from dbtemplates.conf import settings
-from dbtemplates.models import Template, add_template_to_cache, remove_cached_template
+from dbtemplates.models import Template, TemplateSite, add_template_to_cache, remove_cached_template
 from dbtemplates.utils.template import check_template_syntax
 
 # Check if either django-reversion-compare or django-reversion is installed and
@@ -80,6 +81,10 @@ elif settings.DBTEMPLATES_USE_REDACTOR:
     TemplateContentTextArea = RedactorEditor
 
 
+class TemplateSiteInlineAdmin(admin.TabularInline):
+    model = TemplateSite
+
+
 class TemplateAdminForm(forms.ModelForm):
 
     """
@@ -89,11 +94,37 @@ class TemplateAdminForm(forms.ModelForm):
         widget=TemplateContentTextArea(attrs={'rows': '24'}),
         help_text=content_help_text, required=False)
 
+    # https://stackoverflow.com/a/11658199
+    sites = forms.ModelMultipleChoiceField(
+        queryset=TemplateSite.objects.all(),
+        required=False,
+        widget=FilteredSelectMultiple(
+            verbose_name=_("sites"),
+            is_stacked=False,
+        ),
+    )
+
     class Meta:
         model = Template
         fields = ('name', 'content', 'sites', 'creation_date', 'last_changed')
         fields = "__all__"
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        if self.instance.pk:
+            self.fields['sites'].initial = self.instance.sites.all()
+
+    def save(self, commit=True, **kwargs):
+        template = super().save(commit=False, **kwargs)
+        if commit:
+            template.save()
+
+        if template.pk:
+            template.sites = self.cleaned_data['sites']
+            self.save_m2m()
+
+        return template
+
 
 class TemplateAdmin(TemplateModelAdmin):
     form = TemplateAdminForm
@@ -103,17 +134,13 @@ class TemplateAdmin(TemplateModelAdmin):
             'fields': ('name', 'content'),
             'classes': ('monospace',),
         }),
-        (_('Advanced'), {
-            'fields': (('sites'),),
-        }),
         (_('Date/time'), {
             'fields': (('creation_date', 'last_changed'),),
             'classes': ('collapse',),
         }),
     )
-    filter_horizontal = ('sites',)
+    inlines = [TemplateSiteInlineAdmin]
     list_display = ('name', 'creation_date', 'last_changed', 'site_list')
-    list_filter = ('sites',)
     save_as = True
     search_fields = ('name', 'content')
     actions = ['invalidate_cache', 'repopulate_cache', 'check_syntax']

dbtemplates/migrations/0003_templatesite_alter_template_sites_and_more.py

@@ -0,0 +1,44 @@
+# Generated by Django 5.2 on 2025-05-29 20:49
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('dbtemplates', '0002_alter_template_creation_date_and_more'),
+        ('sites', '0002_alter_domain_unique'),
+    ]
+
+    operations = [
+        migrations.SeparateDatabaseAndState(
+            database_operations=[],
+            state_operations=[
+                migrations.CreateModel(
+                    name='TemplateSite',
+                    fields=[
+                        ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                        ('site', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='sites.site')),
+                        ('template', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='dbtemplates.template')),
+                    ],
+                    options={
+                        'db_table': 'django_template_sites',
+                    },
+                ),
+                migrations.AlterField(
+                    model_name='template',
+                    name='sites',
+                    field=models.ManyToManyField(blank=True, through='dbtemplates.TemplateSite', to='sites.site', verbose_name='sites'),
+                ),
+                migrations.AddConstraint(
+                    model_name='templatesite',
+                    constraint=models.UniqueConstraint(fields=('template', 'site'), name='django_template_sites_template_id_site_id_d00c11a4_uniq'),
+                ),
+                migrations.AddConstraint(
+                    model_name='templatesite',
+                    constraint=models.UniqueConstraint(fields=('template__name', 'site'), name='template_name_site_uniq'),
+                ),
+            ],
+        ),
+    ]

dbtemplates/models.py

@@ -9,10 +9,36 @@ from django.contrib.sites.managers import CurrentSiteManager
 from django.contrib.sites.models import Site
 from django.db import models
 from django.db.models import signals
+from django.db.models.constraints import UniqueConstraint
 from django.template import TemplateDoesNotExist
 from django.utils.translation import gettext_lazy as _
 
 
+class TemplateSite(models.Model):
+    """
+    Defines an explicit through model between Template and Site models.
+    This explicit model allows us to add a unique_together index between
+    Site and Template.name
+    """
+    template = models.ForeignKey('Template', on_delete=models.CASCADE)
+    site = models.ForeignKey(Site, on_delete=models.CASCADE)
+
+    class Meta:
+        db_table = 'django_template_sites'
+        constraints = [
+            UniqueConstraint(
+                # Preserve backwards compatibility so we don't have to drop the
+                # old unique index and recreate this index from scratch
+                name='django_template_sites_template_id_site_id_d00c11a4_uniq',
+                fields=['template', 'site'],
+            ),
+            UniqueConstraint(
+                name='template_name_site_uniq',
+                fields=['template__name', 'site'],
+            ),
+        ]
+
+
 class Template(models.Model):
     """
     Defines a template model for use with the database template loader.
@@ -24,7 +50,7 @@ class Template(models.Model):
                             help_text=_("Example: 'flatpages/default.html'"))
     content = models.TextField(_('content'), blank=True)
     sites = models.ManyToManyField(Site, verbose_name=_('sites'),
-                                   blank=True)
+                                   blank=True, through=TemplateSite)
     creation_date = models.DateTimeField(_('creation date'), auto_now_add=True)
     last_changed = models.DateTimeField(_('last changed'), auto_now=True)