Interview question

What is the {% with %} tag used for in Django templates? Django templates में {% with %} tag किस लिए इस्तेमाल होता है?

Answer

{% with %} caches a complex expression (like a chained lookup or method call) into a simple variable name for the duration of a block, avoiding repeated evaluation and improving readability.

<!-- WITHOUT {% with %} - the expensive expression is evaluated MULTIPLE times -->
<p>{{ book.author.profile.bio|truncatewords:20 }}</p>
<p>By {{ book.author.profile.full_name }}</p>
<p>Contact: {{ book.author.profile.email }}</p>
<!-- book.author.profile is resolved three separate times -->

<!-- WITH {% with %} - resolved ONCE, reused via a short name -->
{% with profile=book.author.profile %}
    <p>{{ profile.bio|truncatewords:20 }}</p>
    <p>By {{ profile.full_name }}</p>
    <p>Contact: {{ profile.email }}</p>
{% endwith %}

<!-- Multiple variables in one {% with %} -->
{% with total=book.price count=book.reviews.count %}
    <p>${{ total }} ({{ count }} reviews)</p>
{% endwith %}

<!-- Practical use case: caching a queryset method call result
     that would otherwise hit the database multiple times -->
{% with recent_reviews=book.reviews.all|slice:':5' %}
    <p>{{ recent_reviews|length }} recent reviews</p>
    {% for review in recent_reviews %}
        <p>{{ review.text }}</p>
    {% endfor %}
{% endwith %}

<!-- Note: {{ variable_name }} lookups themselves are relatively cheap in
     Django templates (no repeated DB hits for simple attribute access),
     but {% with %} is valuable when the expression involves a method
     call, filter, or QuerySet evaluation that would otherwise repeat -->

<!-- Scope: variables defined in {% with %} are ONLY available inside
     the {% with %}...{% endwith %} block, not outside it -->

{% with %} किसी complex expression (जैसे chained lookup या method call) को block की duration के लिए simple variable name में cache करता है, repeated evaluation से बचाता है।

<!-- {% with %} के बिना - expensive expression कई बार evaluate होता है -->
<p>{{ book.author.profile.bio|truncatewords:20 }}</p>
<p>By {{ book.author.profile.full_name }}</p>
<p>Contact: {{ book.author.profile.email }}</p>

<!-- {% with %} के साथ - एक बार resolve, फिर reuse -->
{% with profile=book.author.profile %}
    <p>{{ profile.bio|truncatewords:20 }}</p>
    <p>By {{ profile.full_name }}</p>
    <p>Contact: {{ profile.email }}</p>
{% endwith %}

<!-- एक {% with %} में multiple variables -->
{% with total=book.price count=book.reviews.count %}
    <p>${{ total }} ({{ count }} reviews)</p>
{% endwith %}

<!-- Practical उपयोग: queryset method result cache करना -->
{% with recent_reviews=book.reviews.all|slice:':5' %}
    <p>{{ recent_reviews|length }} recent reviews</p>
    {% for review in recent_reviews %}
        <p>{{ review.text }}</p>
    {% endfor %}
{% endwith %}

<!-- Scope: {% with %} में define variables सिर्फ block के अंदर उपलब्ध हैं -->

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