Template fragment caching in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Django template fragment cache do?

Consider this Django template code:

{% load cache %}
{% cache 600 sidebar user.id %}
  <div>User sidebar content</div>
{% endcache %}

What is the effect of this fragment cache?

Django

{% load cache %}
{% cache 600 sidebar user.id %}
  <div>User sidebar content</div>
{% endcache %}

A Caches the sidebar content for 600 seconds separately for each user based on their user ID.

B Caches the sidebar content globally for 600 seconds, ignoring user differences.

C Caches the sidebar content indefinitely until manually cleared.

D Does not cache anything because the cache tag is missing a required argument.

💡 Hint

Look at the cache tag arguments: the first is time in seconds, the second is a cache key prefix, the third is a variable.

The cache tag caches the content for 600 seconds. The cache key includes 'sidebar' and the current user's ID, so each user gets their own cached version.

📝 Syntax

intermediate

Identify the syntax error in this Django template fragment cache usage

What is wrong with this Django template fragment cache code?

{% load cache %}
{% cache '300' 'menu' %}
  <nav>Menu content</nav>
{% endcache %}

Django

{% load cache %}
{% cache '300' 'menu' %}
  <nav>Menu content</nav>
{% endcache %}

A The cache timeout should be an integer without quotes, not a string.

B The endcache tag is missing a required argument.

C The cache tag requires at least one variable argument after the key.

D The cache key 'menu' should not be quoted.

💡 Hint

Check the type of the timeout argument in the cache tag.

The timeout argument must be an integer, not a string. Using quotes makes it a string, causing a syntax error.

🔧 Debug

advanced

Why does this fragment cache not update after the data changes?

Given this template fragment cache:

{% load cache %}
{% cache 900 product_list %}
  <ul>
  {% for product in products %}
    <li>{{ product.name }}</li>
  {% endfor %}
  </ul>
{% endcache %}

When the products list changes, the cached content does not update. Why?

Django

{% load cache %}
{% cache 900 product_list %}
  <ul>
  {% for product in products %}
    <li>{{ product.name }}</li>
  {% endfor %}
  </ul>
{% endcache %}

A The products variable is not passed to the template, so the cache is empty.

B The cache key 'product_list' is static, so the cache never invalidates when products change.

C The cache timeout of 900 seconds is too short to see updates.

D The cache tag requires a user ID to differentiate cache entries.

💡 Hint

Think about how the cache key affects cache invalidation.

Because the cache key is fixed as 'product_list', the cached content stays the same for 900 seconds regardless of product changes. To update cache on data change, the key must include a variable that changes when data changes.

❓ state_output

advanced

What is the output count of cached items with this fragment cache?

If this template fragment cache is used:

{% load cache %}
{% cache 120 comments post.id user.id %}
  <div>Comments section</div>
{% endcache %}

And there are 3 posts and 2 users, how many separate cache entries will be created?

Django

{% load cache %}
{% cache 120 comments post.id user.id %}
  <div>Comments section</div>
{% endcache %}

A 2 cache entries (one per user, ignoring posts).

B 3 cache entries (one per post, ignoring users).

C 6 cache entries (3 posts × 2 users).

D 1 cache entry shared by all posts and users.

💡 Hint

The cache key includes both post.id and user.id.

The cache key is built from 'comments', post.id, and user.id. With 3 posts and 2 users, the combinations are 3 × 2 = 6 unique keys, so 6 cache entries.

🧠 Conceptual

expert

What is the main advantage of using template fragment caching in Django?

Why would a developer choose to use template fragment caching instead of full-page caching in Django?

A It requires no cache key and thus is simpler to implement than other caching methods.

B It caches the entire page content, improving performance for all users equally.

C It automatically updates cached content whenever the database changes without extra code.

D It allows caching parts of a page that are expensive to render while keeping other parts dynamic and personalized.

💡 Hint

Think about when you want some parts of a page to update often and others to stay fast.

Template fragment caching lets you cache only slow parts of a page, so you can keep other parts fresh and personalized, unlike full-page caching which caches everything.