PostgreSQL SIMILAR TO を使いたかった。

config/initializers/arel_override.rb

module ArelVisitorsPostgreSQLOverride
  # https://github.com/rails/rails/blob/v6.0.3.2/activerecord/lib/arel/visitors/postgresql.rb#L29
  def visit_Arel_Nodes_Regexp(o, collector)
    # op = o.case_sensitive ? " ~ " : " ~* "
    op = " SIMILAR TO "
    infix_value o, collector, op
  end
end

Arel::Visitors::PostgreSQL.prepend(ArelVisitorsPostgreSQLOverride)

config/initializers/ransack.rb

Ransack.configure do |config|
  config.add_predicate 'matches_regexp', arel_predicate: 'matches_regexp'
end