Add similar content based on text Trigram similarity

static/src/scss/_similar_content.scss

@@ -0,0 +1,16 @@
+section#similar-content {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  margin-top: 2rem;
+
+  h2 {
+    color: inherit;
+  }
+
+  .media {
+    @include desktop {
+      transform: scale(85%);
+    }
+  }
+}

static/src/scss/base.scss

@@ -20,6 +20,7 @@
 @import "404";
 @import "password_required";
 @import "commento";
+@import "similar_content";
 
 html,
 body {

website/blog/migrations/0005_auto_20230602_1236.py

@@ -0,0 +1,13 @@
+# Generated by Django 4.1.9 on 2023-06-02 12:36
+
+from django.contrib.postgres.operations import TrigramExtension
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("blog", "0004_alter_blogpostcollectionlistpage_body_and_more"),
+    ]
+
+    operations = [TrigramExtension()]

website/blog/models.py

@@ -1,5 +1,6 @@
 from typing import Any, Optional, Type
 
+from django.contrib.postgres.search import TrigramSimilarity
 from django.db import models
 from django.utils import timezone
 from django.utils.functional import cached_property
@@ -66,6 +67,37 @@ class BlogPostPage(BaseContentPage):
     def tag_list_page_url(self) -> Optional[str]:
         return SingletonPageCache.get_url(BlogPostTagListPage)
 
+    def get_similar_posts(self) -> models.QuerySet:
+        try:
+            listing_pages = BlogPostListPage.objects.get().get_listing_pages()
+        except BlogPostListPage.DoesNotExist:
+            return BlogPostPage.objects.none()
+
+        similar_posts = listing_pages.exclude(id=self.id).annotate(
+            title_similarity=TrigramSimilarity("title", self.title),
+            # If this page has no subtitle, ignore it as part of similarity
+            subtitle_similarity=TrigramSimilarity("subtitle", self.subtitle)
+            if self.subtitle
+            else models.Value(1),
+        )
+
+        page_tags = list(self.tags.values_list("id", flat=True))
+        similar_posts = similar_posts.annotate(
+            # If this page has no tags, ignore it as part of similarity
+            tag_similarity=models.Count("tags", filter=models.Q(tags__in=page_tags))
+            / len(page_tags)
+            if page_tags
+            else models.Value(1)
+        )
+
+        similar_posts = similar_posts.annotate(
+            similarity=(models.F("tag_similarity") * 2)
+            * (models.F("title_similarity") * 10)
+            * (models.F("subtitle_similarity"))
+        ).order_by("-similarity")[:3]
+
+        return similar_posts
+
 
 class BlogPostTagListPage(BaseListingPage):
     max_count = 1

website/blog/templates/blog/blog_post_page.html

@@ -1 +1,19 @@
 {% extends "common/content_page.html" %}
+
+{% load cache util_tags %}
+
+{% block post_content %}
+  {{ block.super }}
+
+  {% cache FRAGMENT_CACHE_TTL|jitter:FRAGMENT_CACHE_TTL_JITTER "similar-content" page.id request.is_preview %}
+    <section class="container similar-content" id="similar-content">
+      <h2 class="subtitle is-size-2">Similar content</h2>
+
+      {% for page in page.get_similar_posts %}
+        {% block listing_item %}
+          {% include "common/listing-item.html" %}
+        {% endblock %}
+      {% endfor %}
+    </section>
+  {% endcache %}
+{% endblock %}

website/blog/tests.py

@@ -0,0 +1,49 @@
+from django.test import TestCase
+
+from website.home.models import HomePage
+
+from .factories import BlogPostListPageFactory, BlogPostPageFactory
+
+
+class BlogPostPageTestCase(TestCase):
+    @classmethod
+    def setUpTestData(cls) -> None:
+        cls.home_page = HomePage.objects.get()
+        cls.blog_post_list_page = BlogPostListPageFactory(parent=cls.home_page)
+        cls.page = BlogPostPageFactory(parent=cls.blog_post_list_page)
+
+    def test_accessible(self) -> None:
+        response = self.client.get(self.page.url)
+        self.assertEqual(response.status_code, 200)
+
+    def test_queries(self) -> None:
+        with self.assertNumQueries(45):
+            self.client.get(self.page.url)
+
+
+class BlogPostListPageTestCase(TestCase):
+    @classmethod
+    def setUpTestData(cls) -> None:
+        cls.home_page = HomePage.objects.get()
+        cls.page = BlogPostListPageFactory(parent=cls.home_page)
+
+        BlogPostPageFactory(parent=cls.page)
+        BlogPostPageFactory(parent=cls.page)
+
+    def test_accessible(self) -> None:
+        response = self.client.get(self.page.url)
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(len(response.context["listing_pages"]), 2)
+        self.assertContains(response, self.page.reverse_subpage("feed"))
+
+    def test_queries(self) -> None:
+        with self.assertNumQueries(44):
+            self.client.get(self.page.url)
+
+    def test_feed_accessible(self) -> None:
+        with self.assertNumQueries(12):
+            response = self.client.get(
+                self.page.url + self.page.reverse_subpage("feed")
+            )
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response["Content-Type"], "application/rss+xml; charset=utf-8")