feat: add subcategory support for catalog and admin

- Introduced `Subcategory` model with migration and unique slug constraint per category
- Enabled subcategory assignment for items with validation to ensure category matching
- Updated catalog views to handle subcategories, filtering items accordingly
- Enhanced templates (`index.html`, `side-bar.html`, `item-list.html`, `detail.html`) to display subcategories
- Added dynamic subcategory dropdown in Django admin with category filtering
- Created JavaScript for admin subcategory handling and AJAX population
- Wrote comprehensive tests for subcategory functionality in views and admin

items/admin.py

@@ -1,6 +1,21 @@
+from django import forms
 from django.contrib import admin
+from django.http import JsonResponse
+from django.urls import path
 
-from .models import Category, Item, ItemImage
+from .models import Category, Item, ItemImage, Subcategory
+
+
+def get_subcategory_queryset(category_id):
+    if not category_id:
+        return Subcategory.objects.none()
+
+    try:
+        category_id = int(category_id)
+    except (TypeError, ValueError):
+        return Subcategory.objects.none()
+
+    return Subcategory.objects.filter(category_id=category_id).order_by('name')
 
 
 @admin.register(Category)
@@ -9,6 +24,25 @@ class CategoryAdmin(admin.ModelAdmin):
     prepopulated_fields = {'slug': ('name',)}
 
 
+@admin.register(Subcategory)
+class SubcategoryAdmin(admin.ModelAdmin):
+    list_display = ('name', 'category', 'slug')
+    list_filter = ('category',)
+    prepopulated_fields = {'slug': ('name',)}
+
+
+class ItemAdminForm(forms.ModelForm):
+    class Meta:
+        model = Item
+        fields = '__all__'
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        category_id = self.data.get('category') or getattr(self.instance, 'category_id', None)
+        self.fields['subcategory'].queryset = get_subcategory_queryset(category_id)
+
+
 class ItemImageInline(admin.TabularInline):
     model = ItemImage
     extra = 1
@@ -17,7 +51,33 @@ class ItemImageInline(admin.TabularInline):
 
 @admin.register(Item)
 class ItemAdmin(admin.ModelAdmin):
-    list_display = ('name', 'category', 'price', 'is_available', 'created_at')
-    list_filter = ('is_available', 'category', 'created_at')
+    form = ItemAdminForm
+    list_display = ('name', 'category', 'subcategory', 'price', 'is_available', 'created_at')
+    list_filter = ('is_available', 'category', 'subcategory', 'created_at')
     prepopulated_fields = {'slug': ('name',)}
     inlines = (ItemImageInline,)
+
+    class Media:
+        js = ('items/admin/item-subcategory.js',)
+
+    def get_urls(self):
+        urls = super().get_urls()
+        custom_urls = [
+            path(
+                'subcategories/',
+                self.admin_site.admin_view(self.subcategories_view),
+                name='items_item_subcategories',
+            ),
+        ]
+        return custom_urls + urls
+
+    def subcategories_view(self, request):
+        category_id = request.GET.get('category_id')
+        subcategories = get_subcategory_queryset(category_id)
+
+        return JsonResponse({
+            'subcategories': [
+                {'id': subcategory.id, 'name': subcategory.name}
+                for subcategory in subcategories
+            ],
+        })

items/migrations/0003_subcategory_item_subcategory_and_more.py

@@ -0,0 +1,37 @@
+# Generated by Django 6.0.4 on 2026-04-26 20:49
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('items', '0002_itemimage'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Subcategory',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=255, verbose_name='Название')),
+                ('slug', models.SlugField(verbose_name='URL')),
+                ('category', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='subcategories', to='items.category', verbose_name='Категория')),
+            ],
+            options={
+                'verbose_name': 'Подкатегория',
+                'verbose_name_plural': 'Подкатегории',
+                'ordering': ('category__name', 'name'),
+            },
+        ),
+        migrations.AddField(
+            model_name='item',
+            name='subcategory',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='items', to='items.subcategory', verbose_name='Подкатегория'),
+        ),
+        migrations.AddConstraint(
+            model_name='subcategory',
+            constraint=models.UniqueConstraint(fields=('category', 'slug'), name='unique_subcategory_slug_per_category'),
+        ),
+    ]

items/models.py

@@ -1,4 +1,5 @@
 from django.db import models
+from django.core.exceptions import ValidationError
 
 
 class Category(models.Model):
@@ -13,10 +14,43 @@ class Category(models.Model):
         return self.name
 
 
+class Subcategory(models.Model):
+    category = models.ForeignKey(
+        Category,
+        on_delete=models.CASCADE,
+        related_name='subcategories',
+        verbose_name='Категория',
+    )
+    name = models.CharField(max_length=255, verbose_name='Название')
+    slug = models.SlugField(verbose_name='URL')
+
+    class Meta:
+        ordering = ('category__name', 'name')
+        constraints = [
+            models.UniqueConstraint(
+                fields=('category', 'slug'),
+                name='unique_subcategory_slug_per_category',
+            )
+        ]
+        verbose_name = 'Подкатегория'
+        verbose_name_plural = 'Подкатегории'
+
+    def __str__(self):
+        return self.name
+
+
 class Item(models.Model):
     name = models.CharField(max_length=255, verbose_name='Название')
     slug = models.SlugField(unique=True, verbose_name='URL')
     category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name='items', verbose_name='Категория')
+    subcategory = models.ForeignKey(
+        Subcategory,
+        on_delete=models.SET_NULL,
+        related_name='items',
+        null=True,
+        blank=True,
+        verbose_name='Подкатегория',
+    )
     description = models.TextField(blank=True, verbose_name='Описание')
     price = models.DecimalField(max_digits=10, decimal_places=2, verbose_name='Цена')
     is_available = models.BooleanField(default=True, verbose_name='В наличии')
@@ -30,6 +64,14 @@ class Item(models.Model):
     def __str__(self):
         return self.name
 
+    def clean(self):
+        super().clean()
+
+        if self.subcategory_id and self.category_id and self.subcategory.category_id != self.category_id:
+            raise ValidationError({
+                'subcategory': 'Подкатегория должна относиться к выбранной категории.'
+            })
+
     @property
     def primary_image(self):
         return next(iter(self.images.all()), None)

items/tests.py

@@ -1,6 +1,8 @@
 from django.test import TestCase, override_settings
+from django.contrib.auth import get_user_model
+from django.core.exceptions import ValidationError
 
-from items.models import Category, Item, ItemImage
+from items.models import Category, Item, ItemImage, Subcategory
 
 
 @override_settings(MEDIA_URL="/media/")
@@ -8,10 +10,14 @@ class CatalogViewTests(TestCase):
     def setUp(self):
         self.plumbing = Category.objects.create(name="Сантехника", slug="plumbing")
         self.decor = Category.objects.create(name="Декор", slug="decor")
+        self.sinks = Subcategory.objects.create(name="Мойки", slug="sinks", category=self.plumbing)
+        self.taps = Subcategory.objects.create(name="Смесители", slug="taps", category=self.plumbing)
+        self.decor_lights = Subcategory.objects.create(name="Подсветка", slug="lights", category=self.decor)
         self.sink = Item.objects.create(
             name="Кухонная мойка",
             slug="kitchen-sink",
             category=self.plumbing,
+            subcategory=self.sinks,
             description="Искусственный камень, врезная на столешницу",
             price="1600.00",
             is_available=True,
@@ -20,6 +26,7 @@ class CatalogViewTests(TestCase):
             name="Зеркало Terra",
             slug="terra-mirror",
             category=self.decor,
+            subcategory=self.decor_lights,
             description="Холодная подсветка, фронтальная",
             price="200.00",
             is_available=False,
@@ -39,6 +46,41 @@ class CatalogViewTests(TestCase):
         self.assertContains(response, "Кухонная мойка")
         self.assertNotContains(response, "Зеркало Terra")
 
+    def test_category_page_shows_only_selected_category_subcategories(self):
+        response = self.client.get("/catalog/plumbing/")
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, "Мойки")
+        self.assertContains(response, "Смесители")
+        self.assertNotContains(response, "Подсветка")
+
+    def test_subcategory_page_shows_only_selected_subcategory_items(self):
+        Item.objects.create(
+            name="Смеситель Mono",
+            slug="mono-tap",
+            category=self.plumbing,
+            subcategory=self.taps,
+            description="Однорычажный смеситель",
+            price="320.00",
+            is_available=True,
+        )
+
+        response = self.client.get("/catalog/plumbing/?subcategory=sinks")
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, "Кухонная мойка")
+        self.assertNotContains(response, "Смеситель Mono")
+
+    def test_unknown_subcategory_returns_404(self):
+        response = self.client.get("/catalog/plumbing/?subcategory=unknown")
+
+        self.assertEqual(response.status_code, 404)
+
+    def test_subcategory_from_another_category_returns_404(self):
+        response = self.client.get("/catalog/plumbing/?subcategory=lights")
+
+        self.assertEqual(response.status_code, 404)
+
     def test_unknown_category_returns_404(self):
         response = self.client.get("/catalog/unknown/")
 
@@ -70,6 +112,11 @@ class CatalogViewTests(TestCase):
         self.assertContains(response, "/media/items/primary.jpg")
         self.assertNotContains(response, "/media/items/secondary.jpg")
 
+    def test_item_card_shows_subcategory(self):
+        response = self.client.get("/catalog/")
+
+        self.assertContains(response, "Сантехника / Мойки")
+
     def test_item_card_uses_first_ordered_image_without_primary(self):
         ItemImage.objects.create(
             item=self.sink,
@@ -107,6 +154,7 @@ class CatalogViewTests(TestCase):
 
         self.assertEqual(response.status_code, 200)
         self.assertContains(response, "Кухонная мойка")
+        self.assertContains(response, "Сантехника / Мойки")
         self.assertContains(response, "Искусственный камень")
         self.assertContains(response, "1600,00 руб.")
         self.assertContains(response, "В наличии")
@@ -140,3 +188,51 @@ class CatalogViewTests(TestCase):
         response = self.client.get("/catalog/decor/kitchen-sink/")
 
         self.assertEqual(response.status_code, 404)
+
+    def test_item_subcategory_must_belong_to_item_category(self):
+        item = Item(
+            name="Некорректный товар",
+            slug="invalid-item",
+            category=self.plumbing,
+            subcategory=self.decor_lights,
+            description="",
+            price="100.00",
+            is_available=True,
+        )
+
+        with self.assertRaises(ValidationError):
+            item.full_clean()
+
+    def test_admin_subcategories_endpoint_filters_by_category(self):
+        user = get_user_model().objects.create_superuser(
+            username="admin",
+            email="admin@example.com",
+            password="password",
+        )
+        self.client.force_login(user)
+
+        response = self.client.get(f"/admin/items/item/subcategories/?category_id={self.plumbing.id}")
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(
+            response.json(),
+            {
+                "subcategories": [
+                    {"id": self.sinks.id, "name": "Мойки"},
+                    {"id": self.taps.id, "name": "Смесители"},
+                ]
+            },
+        )
+
+    def test_admin_subcategories_endpoint_returns_empty_without_category(self):
+        user = get_user_model().objects.create_superuser(
+            username="admin",
+            email="admin@example.com",
+            password="password",
+        )
+        self.client.force_login(user)
+
+        response = self.client.get("/admin/items/item/subcategories/")
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.json(), {"subcategories": []})

items/views.py

@@ -3,7 +3,7 @@ from dataclasses import dataclass
 from django.http import HttpRequest, HttpResponse, Http404
 from django.shortcuts import render
 
-from items.models import Category, Item
+from items.models import Category, Item, Subcategory
 
 
 @dataclass
@@ -12,9 +12,25 @@ class SelectedCategory:
     id: str | None
 
 
+@dataclass
+class SelectedSubcategory:
+    name: str | None
+    id: str | None
+
+
 def index(request: HttpRequest, category: str | None = None) -> HttpResponse:
     selected_category = SelectedCategory(name=None, id=None)
-    items = Item.objects.select_related('category').prefetch_related('images').order_by('category__name', 'name')
+    selected_subcategory = SelectedSubcategory(name=None, id=None)
+    subcategories = Subcategory.objects.none()
+    subcategory_slug = request.GET.get('subcategory')
+    items = (
+        Item.objects.select_related('category', 'subcategory')
+        .prefetch_related('images')
+        .order_by('category__name', 'name')
+    )
+
+    if category is None and subcategory_slug:
+        raise Http404()
 
     if category is not None:
         try:
@@ -22,19 +38,31 @@ def index(request: HttpRequest, category: str | None = None) -> HttpResponse:
             selected_category = SelectedCategory(name=cat.name, id=cat.slug)
         except Category.DoesNotExist:
             raise Http404()
+        subcategories = Subcategory.objects.filter(category=cat).order_by('name')
         items = items.filter(category=cat)
 
+        if subcategory_slug:
+            try:
+                subcategory_obj = subcategories.get(slug=subcategory_slug.lower())
+                selected_subcategory = SelectedSubcategory(name=subcategory_obj.name, id=subcategory_obj.slug)
+            except Subcategory.DoesNotExist:
+                raise Http404()
+
+            items = items.filter(subcategory=subcategory_obj)
+
     return render(request, 'catalog/index.html', {
         'categories': Category.objects.order_by('name'),
+        'subcategories': subcategories,
         'items': items,
-        'selected_category': selected_category
+        'selected_category': selected_category,
+        'selected_subcategory': selected_subcategory,
     })
 
 
 def detail(request: HttpRequest, category: str, slug: str) -> HttpResponse:
     try:
         item = (
-            Item.objects.select_related('category')
+            Item.objects.select_related('category', 'subcategory')
             .prefetch_related('images')
             .get(category__slug=category.lower(), slug=slug)
         )

static/items/admin/item-subcategory.js

@@ -0,0 +1,67 @@
+(function () {
+    function getSubcategoriesUrl() {
+        return window.location.pathname.replace(/\/(?:add|\d+\/change)\/?$/, '/subcategories/');
+    }
+
+    function setOptions(select, subcategories, selectedId) {
+        var emptyOption = Array.prototype.find.call(select.options, function (option) {
+            return option.value === '';
+        });
+        var emptyLabel = emptyOption ? emptyOption.textContent : '---------';
+
+        select.innerHTML = '';
+        select.appendChild(new Option(emptyLabel, ''));
+
+        subcategories.forEach(function (subcategory) {
+            var option = new Option(subcategory.name, subcategory.id);
+
+            if (String(subcategory.id) === String(selectedId)) {
+                option.selected = true;
+            }
+
+            select.appendChild(option);
+        });
+    }
+
+    function loadSubcategories(categorySelect, subcategorySelect, selectedId) {
+        if (!categorySelect.value) {
+            setOptions(subcategorySelect, [], '');
+            return;
+        }
+
+        var url = getSubcategoriesUrl() + '?category_id=' + encodeURIComponent(categorySelect.value);
+
+        fetch(url, {
+            headers: {
+                'X-Requested-With': 'XMLHttpRequest'
+            }
+        })
+            .then(function (response) {
+                if (!response.ok) {
+                    throw new Error('Failed to load subcategories.');
+                }
+
+                return response.json();
+            })
+            .then(function (data) {
+                setOptions(subcategorySelect, data.subcategories || [], selectedId);
+            });
+    }
+
+    document.addEventListener('DOMContentLoaded', function () {
+        var categorySelect = document.getElementById('id_category');
+        var subcategorySelect = document.getElementById('id_subcategory');
+
+        if (!categorySelect || !subcategorySelect) {
+            return;
+        }
+
+        categorySelect.addEventListener('change', function () {
+            loadSubcategories(categorySelect, subcategorySelect, '');
+        });
+
+        if (!categorySelect.value) {
+            setOptions(subcategorySelect, [], '');
+        }
+    });
+}());

templates/catalog/_fragments/item-list.html

@@ -14,7 +14,9 @@
                 {% endwith %}
 
                 <div class="item-card-body">
-                    <div class="item-card-category">{{ item.category.name }}</div>
+                    <div class="item-card-category">
+                        {{ item.category.name }}{% if item.subcategory %} / {{ item.subcategory.name }}{% endif %}
+                    </div>
                     <h2 class="item-card-title">{{ item.name }}</h2>
                     <div class="item-card-footer">
                         <span class="item-card-price">{{ item.price }} руб.</span>

templates/catalog/_fragments/side-bar.html

@@ -13,6 +13,20 @@
 
     <section class="sub-categories a-section">
         <h2>Подкатегории</h2>
+        {% if selected_category.id != None %}
+            <a href="/catalog/{{ selected_category.id }}/" class="category {% if selected_subcategory.id == None %}active{% endif %}">
+                Все подкатегории
+            </a>
+            {% for subcategory in subcategories %}
+                <a href="/catalog/{{ selected_category.id }}/?subcategory={{ subcategory.slug }}" class="category {% if selected_subcategory.id == subcategory.slug %}active{% endif %}">
+                    {{ subcategory.name }}
+                </a>
+            {% empty %}
+                <p class="categories-empty">Подкатегории пока не добавлены.</p>
+            {% endfor %}
+        {% else %}
+            <p class="categories-empty">Выберите категорию.</p>
+        {% endif %}
     </section>
 
     <form action="">

templates/catalog/detail.html

@@ -37,7 +37,9 @@
         </section>
 
         <section class="product-summary" aria-label="Информация о товаре">
-            <p class="product-summary__category">{{ item.category.name }}</p>
+            <p class="product-summary__category">
+                {{ item.category.name }}{% if item.subcategory %} / {{ item.subcategory.name }}{% endif %}
+            </p>
             <h1 class="product-summary__title">{{ item.name }}</h1>
 
             <div class="product-summary__meta">

templates/catalog/index.html

@@ -13,12 +13,18 @@
 
     {% if selected_category.id == None %}
         {% include '_fragments/breadcrumbs.html' with url_1='/' text_1='Главная' url_2='/catalog/' text_2='Каталог' %}
+    {% elif selected_subcategory.id != None %}
+        {% with category_url='/catalog/'|add:selected_category.id|add:'/' subcategory_url='/catalog/'|add:selected_category.id|add:'/?subcategory='|add:selected_subcategory.id %}
+            {% include '_fragments/breadcrumbs.html' with url_1='/' text_1='Главная' url_2='/catalog/' text_2='Каталог' url_3=category_url text_3=selected_category.name url_4=subcategory_url text_4=selected_subcategory.name %}
+        {% endwith %}
     {% else %}
-        {% include '_fragments/breadcrumbs.html' with url_1='/' text_1='Главная' url_2='/catalog/' text_2='Каталог' text_3=selected_category.name %}
+        {% with category_url='/catalog/'|add:selected_category.id|add:'/' %}
+            {% include '_fragments/breadcrumbs.html' with url_1='/' text_1='Главная' url_2='/catalog/' text_2='Каталог' url_3=category_url text_3=selected_category.name %}
+        {% endwith %}
     {% endif %}
 
     <div class="container catalog-container">
-        {% include 'catalog/_fragments/side-bar.html' with categories=categories selected_category=selected_category %}
+        {% include 'catalog/_fragments/side-bar.html' with categories=categories subcategories=subcategories selected_category=selected_category selected_subcategory=selected_subcategory %}
 
         {% include 'catalog/_fragments/item-list.html' with items=items %}
     </div>