使用具有has_many关系的复选框

class Post< ApplicationRecord
  has_many :post_tags
  has_many :tags, through: :post_tags
end

class Tag< ApplicationRecord
  has_many :post_tags
  has_many :posts, through: :post_tags
end

<%= form_with(model: post) do |form| %>
  <%= form.label :title %>
  <%= form.text_field :title %>

  <%= form.label :content %>
  <%= form.text_area :content %>

  <%= form.label :tags %>
  <%= form.collection_check_boxes(:tag_ids, Tag.all, :id, :name) do |tag| %>
    <%= tag.label do %>
      <%= tag.check_box %>
      <%= tag.text %>
    <% end %>
  <% end %>

  <%= form.submit %>
<% end %>