Check if category is assigned in channel entry conditional

Question

I am trying to use templates in embeds depending on the users' category selection but I don't know how to check if a category has been assigned or not.

{categories}
    {if category_url_title=="full-page-review"}
        {embed="temp-group/.full_page_review" entry_id="{entry_id}"}
    {if:elseif category_url_title=="standard"}
        {embed="temp-group/.standard" entry_id="{entry_id}"}
    {/if}
{/categories}

This works fine as long as a category has been assigned in the entry, but nothing happens if the author forgot to assign a category. Is there a way to see if there is a category assigned or not while using a conditional like this?

Answer 1

I was able to accomplish what I was after using the following...

{if "{categories}{category_url_title}{/categories}"!=""}
    CATEGORY EXISTS
{if:else}
    NO CATEGORY EXISTS
{/if}

Answer 2

I use Switchee to check for the length of a string (e.g. for a change in design if title is too long). I suppose it could be adapted to check if the string is empty or not:

      {exp:switchee parse="inward" variable="{categories}{category_url_title}{/categories}"}
        {case value="full-page-review"}
          {embed="temp-group/.full_page_review" entry_id="{entry_id}"}
        {/case}
        {case value="standard"}
          {!-- just here as an example --}
          {embed="temp-group/.standard" entry_id="{entry_id}"}
        {/case}
        {case value="#^.{1,}$#"} 
        {!-- regex of ^.{1,}$ means match any character of 1 or more,
             I would have another number after the comma though. 
             You could just try #^.+$# instead, don't see why that wouldn't work --}
          {!-- unaccounted for case, but category exists --}
          {embed="temp-group/.standard" entry_id="{entry_id}"}
        {/case}
        {case default="Yes"}
          {!-- unaccounted for case, category DNE --}
          {embed="temp-group/.standard" entry_id="{entry_id}"}
        {/case}
      {/exp:switchee}

The above assumes that {category_url_title} will not leave whitespace before/after it.