Twig for loop - output only parent if any children exists

Question

These lines prints all categories and the products within. But if the category has no products the category title is still printed.

{% for category in categories %}
  <h1>{{ category.title }}</h1>
  {% for product in products if products.category|first == category.title|lower %}
    <h2>{{ product.title }}</h2>
  {% endfor %}
{% endfor %}

How can I optimize this so category titles are printed only when the category contains products?

Answer 1

There are (imo) 2 solution for this. The first one is pure twig-based, but is the worst of the two methods.

In order to skip categories without children, this would require a second loop and flag variable to determine wether to skip the category or not. As twig can't break out of loops this means u would need to foreach the products twice completely

{% for category in categories %}
  {% set flag = false %}
  {% for product in products if products.category|first == category.title|lower %}   
    {% set flag = true %}
  {% endfor %}
  {% if flag %}
      <h1>{{ category.title }}</h1>
      {% for product in products if products.category|first == category.title|lower %}
        <h2>{{ product.title }}</h2>
      {% endfor %}
  {% endif %}
{% endfor %}

---

The second and better solution is just to add an extra method to your category-model and do something like

{% for category in categories if category.hasProducts() %}
  <h1>{{ category.title }}</h1>
  {% for product in products if products.category|first == category.title|lower %}
    <h2>{{ product.title }}</h2>
  {% endfor %}
{% endfor %}

Answer 2

An easy solution would be to add a is defined condition to your twig loop. Example:

{% for category in categories if categories is defined %}
  <h1>{{ category.title }}</h1>
  {% for product in products if products.category|first == category.title|lower %}
    <h2>{{ product.title }}</h2>
  {% endfor %}
{% endfor %}