gistfile1.txt

<form action="{{ path('itemtemplate_update', { 'id': entity.id }) }}" method="post" {{ form_enctype(edit_form) }}>
    {{ form_errors(edit_form) }}
    {{ form_row(edit_form.name) }}
    {{ form_row(edit_form.vendor) }}
    {{ form_row(edit_form.sku) }}
    <br />
    {% for trait in edit_form.trait %}
    {{ form_row(trait) }}
    {% endfor %}
    {{ form_rest(edit_form) }}
    <p>
        <button type="submit">Edit</button>
    </p>
</form>

//================

    /**
     * @var ArrayCollection $traits
     *
     * @ORM\OneToMany(targetEntity="Trait", mappedBy="template")
     */
    private $traits;