Update select.html

In relations.py:
relations.py:PrimaryKeyRelatedField.to_representation mostly (by default) returns an integer, but RelatedField.choices converts all to the string. That is why "select" field on "update" action, usually does not work correctly.

rest_framework/templates/rest_framework/vertical/select.html

@@ -11,7 +11,7 @@
     {% endif %}
 
     {% for key, text in field.choices.items %}
-      <option value="{{ key }}" {% if key == field.value %}selected{% endif %}>{{ text }}</option>
+      <option value="{{ key }}" {% if key == field.value|slugify %}selected{% endif %}>{{ text }}</option>
     {% endfor %}
   </select>