The hierarchical category function is created with rails.
Functionally, there is no problem (category2 is displayed after selecting category1), but an error occurs when the post button is pressed, and the post is not saved.

Errors encountered

ActiveModel :: UnknownAttributeError in PostsController # create
unknown attribute 'category1_id' for Post.

The first time I encountered an error, I couldn't resolve it even after checking it, and I was stuck.
When you check your terminal,

"category1_id" =>"1", "category2_id" =>"1", "category3_id" =>"1"

Since the category id is properly taken like this, I don't know what this error indicates.
I think that the place where I feel a little uncomfortable is the processing of @post given to the post form.

Association is a little complicated and may be wrong at that point
Please give me a professor.

Code

create_table "category1s", options: "ENGINE = InnoDB DEFAULT CHARSET = utf8", force:: cascade do | t |
    t.string "name"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end
  create_table "category2s", options: "ENGINE = InnoDB DEFAULT CHARSET = utf8", force:: cascade do | t |
    t.string "name"
    t.bigint "category1_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["category1_id"], name: "index_category2s_on_category1_id"
  end
  create_table "category3s", options: "ENGINE = InnoDB DEFAULT CHARSET = utf8", force:: cascade do | t |
    t.string "name"
    t.bigint "category2_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["category2_id"], name: "index_category3s_on_category2_id"
  end
  create_table "posts", options: "ENGINE = InnoDB DEFAULT CHARSET = utf8", force:: cascade do | t |
    t.string "name"
    t.text "content"
    t.integer "price"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "image"
    t.string "status"
    t.integer "user_id"
    t.string "category1"
    t.string "category2"
    t.string "category3"
  end

<% category1_options = Category1.order (: id) .map {| c | [c.name, c.id, data: {children_path: category1_category2s_path (c)}]}%>
  <% = f.select: category1_id, category1_options, {prompt: "---"}, class: 'select-parent select-default'%>
  <% category2s = @ post.category1.try (: category2s) || []%>
  <% category2_options = category2s.map {| c | [c.name, c.id, data: {path: category1_category2_category3s_path (c)}]}%>
  <% = f.select: category2_id, category2_options, {prompt: "---"}, class: 'select-children select-default', style: "display: none;"%>
  <% category3s = @ post.category2.try (: category3s) || []%>
  <% category3_options = category3s.map {| c | [c.name, c.id]}%>
  <% = f.select: category3_id, category3_options, {prompt: "---"}, class: 'select-grandchildren select-default', style: "display: none;"%>

class PostsController</pre>
<pre><code>resources: category1s, only: [] do
    resources: category2s, only:: index do
      resources: category3s, only:: index
    end
  end

belongs_to: category1
  belongs_to: category2
  belongs_to: category3

has_many: category2s,->{order (: id)}

belongs_to: category1, optional: true
  has_many: category3s,->{order (: id)}

belongs_to: category2, optional: true