Merge pull request #58 from ankitamk14/homepage

query optimization for homepage scroller

Author: sunilshetye

static/website/templates/index.html

@@ -25,30 +25,45 @@
 
 
 </script>
-    <div id="carousel-container">
-        <div class="carousel">
-            {% for category in categories %}
-                <div>
-                    <div class="thumbnail">
-                        {% with file=category|get_category_image %}
-                            {% if file %}
-                                <img src="{% static category|get_category_image %}">
-                            {% else %}
-                                <div class="category-title">{{category}}</div>
-                            {% endif %}
-                        {% endwith %}
-                        <div class="caption">
-                            <small class="category">
-                                {{ category }}
-                            </small>
-                            {% latest_question category %}
-                            <a class="btn btn-xs btn-block btn-success" href="{% url 'website:new_question' %}?category={{ category|urlencode }}">Ask new question</a>
-                        </div>
+<div id="carousel-container">
+    <div class="carousel">
+        {% for category, data in category_question_map.items %}
+            <div>
+                <div class="thumbnail">
+                    {% with file=category|get_category_image %}
+                        {% if file %}
+                            <img src="{% static category|get_category_image %}">
+                        {% else %}
+                            <div class="category-title">{{category}}</div>
+                        {% endif %}
+                    {% endwith %}
+
+                    <div class="caption">
+                        
+                        <small class="category">
+                            {{ category }}
+                        </small>
+                        {% if data %}
+                        <small class="latest">
+                            <a href="{% url 'website:get_question' data.id %}">{{ data.question }}</a>
+                        </small>
+                        <a class="btn btn-xs btn-block btn-primary" href="{% url 'website:filter' data.foss_url %}">View previous questions</a>
+                    {% else %}
+                        <small class="latest">
+                            Be the first to ask question.
+                        </small>
+                        <a class="btn btn-block btn-xs">
+                            No questions to display
+                        </a>
+                    {% endif %}
+                        <a class="btn btn-xs btn-block btn-success" href="{% url 'website:new_question' %}?category={{ category|urlencode }}">Ask new question</a>
                     </div>
                 </div>
-            {% endfor %}
-        </div> <!-- /.carousel -->
-    </div> <!-- /#carousel-container -->
+            </div>
+        {% endfor %}
+    </div> <!-- /.carousel -->
+</div> <!-- /#carousel-container -->
+   
 
     <div id="filter-container">
         <div class="row">

website/views.py

@@ -4,7 +4,7 @@
 from django.shortcuts import render, get_object_or_404
 from django.template.context_processors import csrf
 from django.contrib.auth.decorators import login_required
-from django.db.models import Q
+from django.db.models import Q, OuterRef, Subquery, Max, Count
 from django.core.mail import EmailMultiAlternatives
 from django.core.paginator import Paginator, EmptyPage, PageNotAnInteger
 from django.contrib.auth import get_user_model
@@ -17,7 +17,6 @@
 from website.templatetags.permission_tags import can_edit, can_hide_delete
 from spoken_auth.models import FossCategory
 from .sortable import SortableHeader, get_sorted_list, get_field_index
-from django.db.models import Count
 
 
 User = get_user_model()
@@ -32,11 +31,39 @@
 def home(request):
     questions = Question.objects.filter(status=1).order_by('date_created').reverse()[:100]
     active_questions = Question.objects.filter(status=1, last_active__isnull=False).order_by('last_active').reverse()[:100]
+
+    # Retrieve latest questions per category for the slider
+    subquery = Question.objects.filter(category=OuterRef('category'), status=1).values('category').annotate(max_date=Max('date_created')).values('max_date')
+    slider_questions = Question.objects.filter(
+            date_created=Subquery(subquery), status=1
+    ).order_by('category')
+
+    # Mapping of foss name as in spk db & its corresponding category name in forums db
+    category_fosses = {val.replace(" ", "-") : val for val in categories}    
+
+    # All eligible categories to be shown in homepage slider
+    all_eligible_categories = list(category_fosses.keys())
+    
+    # Create a dictionary to map categories to questions for the slider
+    category_question_map = {}
+    for question in slider_questions:
+        if question.category in all_eligible_categories:
+            foss = category_fosses.get(question.category)
+            category_question_map[foss] = {"id" : question.id, "question": question.title, "foss_url": question.category}
+    
+    # Fill in missing categories without questions
+    for category in category_fosses.keys():
+        foss = category_fosses.get(category)
+        if foss not in category_question_map:
+            category_question_map[foss] = None
+    
+    # Sort category_question_map by category name
+    category_question_map = dict(sorted(category_question_map.items(), key= lambda item: item[0].lower()))
     context = {
-        'categories': categories,
-        'questions': questions,
-        'active_questions':active_questions
-    }
+    'questions': questions,
+    'active_questions':active_questions,
+    'category_question_map': category_question_map
+}
     return render(request, "website/templates/index.html", context)