Frontend form database error with empty Users field

Question

Within a frontend Add Product form (using Craft Commerce) I'm having problems with a database error whenever a Users field is left empty.

Here's the field:

{% set teachers = craft.users.group('teachers') %}
<select name="fields[teacher][]">
<option value="">n/a</option>
{% for teacher in teachers %}
  <option value="{{ teacher.id }}">{{ teacher.name }}</option>
{% endfor %}
</select>

I've tried setting the empty value to zero, but no luck. The forms works fine apart from this, so I don't think it's anything specific to Craft Commerce.

Answer 1

Figured it out. If you want to return an empty Users field, the field name attribute has to look like this:

<select name="fields[teacher]" value="">

But if you want to return a non-empty Users field, the name attribute is different:

<select name="fields[teacher][]" value="{user.id}">

So, I'm starting with the first example, and using an onChange event to switch the name attribute depending on whether the value is a valid user ID or not. Here's my final template code:

{% set teachers = craft.users.group('teachers') %}
<select class="ui search dropdown" name="fields[teacher]" id="teacherselect">
<option value="nA">n/a</option>
{% for teacher in teachers %}
  <option value="{{ teacher.id }}">{{ teacher.name }}</option>
{% endfor %}
</select>

And the jquery if anyone wants it:

($(this).val() == "nA") ? $(this).attr('name', 'fields[teacher]') : $(this).attr('name', 'fields[teacher][]')

This works.

Answer 2

Yep, seen this before. You can't just have an empty value like that because the validation stuff just sees it as a missing field that's required to not be missing. We got around it by adding the n/a value into the field itself in the back end of Craft.

Which doesn't help you for User Groups unless you want to create an 'n/a' group.