file_upload.pt

<p tal:define="preview_url cstruct.get('preview_url')">
<a tal:condition="preview_url" href="${structure: preview_url}"
                                     target="_blank">Show</a>
<p tal:condition="not preview_url" id="${oid|field.oid}"
                                   class="form-control-static deform-readonly-text"
         tal:content="cstruct.get('filename') or ''"></p>
</p>