title: Strange issue with setting custom foreign_key
body: <p>From the documentation I read that:</p>
  
  <pre><code>class Book &lt; ApplicationRecord
    belongs_to :author, class_name: "Patron", foreign_key: "patron_id"
  end
  </code></pre>
  
  <p>so according to that I'm trying the next:</p>
  
  <pre><code>class Choco &lt; ActiveRecord::Base
    has_many :kinds, inverse_of: :choco, foreign_key: :myhash
  </code></pre>
  
  <p>and</p>
  
  <pre><code>class Kind &lt; ActiveRecord::Base
    belongs_to :choco, foreign_key: :myhash
  </code></pre>
  
  <p>But instead it pastes in that column NULL and I cannot understand why.</p>
  
  <p><strong>Schema</strong></p>
  
  <p>For Choco:</p>
  
  <pre><code>— (id, title, myhash)
  </code></pre>
  
  <p>For Kind:</p>
  
  <pre><code>— (id, choco_id, title)
  </code></pre>
  
  <p>I want to paste myhash on choco_id field on creating a new kind.</p>
  
  <p>What is the problem?</p>