{% trans_default_domain 'admin' %}

<input type="file" id="{{ form.vars.id }}" name="{{ form.vars.full_name }}" class="filestyle" data-classButton="btn btn-primary" data-input="false" data-classIcon="icon-plus" data-buttonText="{{ form.vars.label }}"/>
{# the following code works great, except when creating new file, then an error in thrwn during the template render #}
{% set file = form.vars.sonata_admin.admin.subject is defined ? form.vars.sonata_admin.admin.subject : null %}
{% if file %}
  {% set filePath = file.fileUrl is defined ? file.fileUrl : file.externalImageUrl is defined ? file.externalImageUrl : null %}
  {% set extension = filePath|split('.')|last|lower %}
  {% if filePath %}
    {% if extension in ['jpg', 'jpeg', 'png', 'gif', 'svg'] %}
      <img src="{{ filePath }}" class="thumbnail"/>
    {% else %}
      {{ 'commons.actual_file'|trans }} <i>{{ filePath|split('/')|last }}</i>
    {% endif %}
  {% endif %}
{% endif %}

<style>
  .thumbnail {
    width: 100px;
    display: inline-block;
    margin-right: 10px;
  }
</style>