title: Check if multiple records exist with ActiveRecord?
body: <p>Using <code>#exists?</code> gives a false positive (i.e. will return true) when at least one of the keys exist.</p>
  
  <pre><code>MyModel.exist?(key: [:risk_score, :i_made_this_up]) # =&gt; true
  </code></pre>
  
  <p>For a small number of checks I could do:</p>
  
  <pre><code>[:risk_score, :i_made_this_up].all? { |key| MyModel.exists?(key: key) }
  </code></pre>
  
  <p>But this is an N+1 query, what if I have many keys to check? </p>