Anti patterns

Anti-Patterns & Common Mistakes

When to Use

Code review checklist. Review your templates against these patterns before committing.

Anti-Patterns

1. Logic in templates Twig templates are presentation layer. Business logic belongs in PHP.

{# WRONG — calculating in template #}
{% set words = node.field_body.value|split(' ')|length %}
{% set minutes = (words / 200)|round %}
Reading time: {{ minutes }} minutes

{# RIGHT — calculate in preprocess #}
Reading time: {{ reading_time }} minutes

2. Accessing content array like it's field objects

{# WRONG — content is a render array, not field objects #}
{% if content.field_tags.value %}
{% for tag in content.field_tags %}

{# RIGHT — use node object for raw access, content for rendering #}
{% if node.field_tags is not empty %}
{{ content.field_tags }}

3. Not using |without() — double-rendering fields

{# WRONG — field_image renders twice #}
<div class="hero">{{ content.field_image }}</div>
{{ content }}  {# field_image renders again here #}

{# RIGHT — exclude from catch-all #}
<div class="hero">{{ content.field_image }}</div>
{{ content|without('field_image') }}

4. Hard-coded paths to theme assets

{# WRONG — breaks when theme moves, no cache busting #}
<img src="/themes/custom/mytheme/images/logo.svg">

{# RIGHT — use library system or active_theme_path() sparingly #}
{{ attach_library('mytheme/header') }}
{# Or in preprocess: #}
{# $variables['logo_url'] = $theme_path . '/images/logo.svg'; #}

5. Bypassing field formatters for display

{# WRONG — bypasses formatters, breaks field display config, no cache metadata #}
<p>{{ node.field_body.value|raw }}</p>

{# RIGHT — respects display config, formatters, text filters #}
{{ content.field_body }}

6. PHP-in-Twig patterns (twig_tweak |php filter)

{# WRONG — arbitrary PHP in templates is a security nightmare #}
{{ 'SomeClass::method()'|php }}

{# RIGHT — use preprocess functions or proper Twig extensions #}
{{ my_preprocess_variable }}

7. Not checking for empty entity references before traversal

{# WRONG — crashes if field is empty #}
<img src="{{ file_url(node.field_image.entity.fileUri) }}">

{# RIGHT — guard against empty fields #}
{% if node.field_image.entity %}
  <img src="{{ file_url(node.field_image.entity.fileUri) }}">
{% endif %}

8. Using template preprocess for data that belongs in field formatters If you're rewriting how a field renders in preprocess + template, consider: should this be a custom field formatter instead? Formatters are reusable, configurable in the UI, and cacheable properly.

9. Entity traversal in Twig for display output (cache invalidation bypass)

{# WRONG — loads term entity in Twig; its cache tags never bubble.
   If the term gets renamed, cached pages show the old name. #}
{% set term = node.field_category.entity %}
<span>{{ term.label }}</span>

{# RIGHT — load in preprocess, bubble cache tags #}
<span>{{ category_label }}</span>

See Accessing Field Values — Cache Invalidation Warning for the preprocess pattern with addCacheableDependency().

10. Modifying render arrays destructively in templates

{# WRONG — `without` takes the name as a string argument, not like this #}
{% set custom_content = content %}
{% unset custom_content.field_image %}  {# This doesn't work in Twig #}

{# RIGHT #}
{{ content|without('field_image') }}

Anti patterns

Anti-Patterns & Common Mistakes

When to Use

Anti-Patterns

See Also