You apparently can’t combine include_blank and required on a select box, which seems odd.

by John Norris

I can imagine we’d often want to give users a choice of options (with no default) but insist they pick one.

It looks like this is possible, although you have to do a bit of a workaround by using prompt on the select box, which adds a “no value” option, and then give that no display value, e.g.

<%= form.select :name, options_for_select(options), { prompt: "" }, required: true %>