Rails: how to create a migration that add 'using: :btree' to foreign key
<p>I have two models<br>
father has_many sons<br>
son belongs_to father</p>

<p>Normally, this piece of code</p>

<pre><code>def change
    add_reference :sons, :father, index: true
end
</code></pre>

<p>it will generate</p>

<pre><code>add_index "sons", ["father_id"], name: "index_sons_on_father_id"
</code></pre>

<p>Now, I want it generate </p>

<pre><code>add_index "sons", ["father_id"], name: "index_sons_on_father_id", using: :btree
</code></pre>

<p>How to write the migration?</p>