How to use select dropdown with entries/saveEntry for an entry field?

Question

How to use select dropdown with entries/saveEntry for an entry field?

I have an entry with a field that is another entry, which I want to update with a form:

<form method="post" accept-charset="UTF-8">
  {{ getCsrfInput() }}
  <input type="hidden" name="action" value="entries/saveEntry">
  <input type="hidden" name="entryId" value="{{ entry.id }}">
  <label>Vendor
    <select name="fields[vendor][]">
      <option>---</option>
      {% for v in craft.entries.section('vendors') %}
        <option value="{{v.id}}">{{v.title}}</option>
      {% endfor %}
    </select>
  </label>
  <input type="submit" value="Submit"/>
</form>

This works fine, except if nothing is selected in the dropdown (<option>---</option>). In that case, the POST value for fields[vendor][] is ---, and I get a SQL foreign key constraint error.

I have also tried <option value="">---</option> and <option value="NULL">---</option> with no better outcome.

Answer 1

I ran into this a while ago and it drove me nuts. Try adding disabled and selected attributes to your initial option in the select. So in your case <option disabled selected>---</option>.