simple_form_for 中 association 的使用

# model
class Question < ApplicationRecord
    has_many :invitated_users, through: :question_invitations, source: :user
end

# html
<%= f.association :invitated_users, :as => :check_boxes, label: false,selected: @question.invitated_users %>

# controller
# strong params 中加入

params.require(:question).permit(:invitated_user_ids=>[] )

即可自动保存关系