Relating to Solspace Calendar Events I'm using Solspace Calendar for events, I also have a standard channel for reviews. What I need is the ability to connect the review with the event. 

Solspace offers "Calendar Events" custom type field to do that, however, when I use it and attach an event to it this code:

{% set reviews = craft.entries.section('reviews').relatedTo(event) %}
{% if reviews|length %}
   {% for review in reviews %}
      &lt;h5&gt;{{review.title}}&lt;/h5&gt;
      &lt;p&gt;{{review.description|nl2br}}&lt;/p&gt;
   {% endfor %}
{% else %}
   &lt;p&gt;There are no reviews yet&lt;/p&gt;
{% endif %}


isn't working, and I have the same code working for a standard entry. How do I use relatedTo on custom fields?

This works on a different page with entry present

{% set reviews = craft.entries.section('reviews').relatedTo(entry) %}


This doens't work when event present

{% set reviews = craft.entries.section('reviews').relatedTo(event) %}


I've made sure that: 


the event is fetched, and I'm successfully accessing it via code above
there are indeed reviews with this event attached
You can use them the same way like you are used to everywhere else. All relation fields extend the same BaseRelationField so their logic is totally equal.

You can either pass an element, an element id or an ElementQuery/ElementCriteriaModel but not a string to the function. If you want to fetch all related elements of an event you'll need to fetch the event first