title: How to search for an array length in ecto
body: <p>Let say I have a schema</p>
  
  <pre><code>defmodule User do
    use MyApp.Web, :model
  
    schema "users" do
      field :loved_numbers, {:array, :integer} 
    end
  end
  </code></pre>
  
  <p>How could I search using <code>Ecto.Query</code> for all users who have exactly 2 <code>loved_numbers</code>?</p>
  
  <p>Would this query work in both PostgreSQL and MySQL?</p>