carrierwaveで画像をアップロードする際のコントローラー側の処理

Question

いつもお世話になります。
画像と文字を投稿し表示できるようなページをRailsで作成しております。いろいろなサイトを参考にcarrierwaveのインストールを行いコードを以下のように書いている状態です。

投稿者名（poster_name）、投稿内容（post_text）、イメージ用のパス（attachment_name）の3つをActiveRecordに保存したいのですが、attachment_nameの保存の部分が分かりません。

コントローラー側の処理について解説しているサイトが少なくこちらに質問させて頂きました。

ご教示のほどお願いいたします。

環境はローカルです。

以下パラメータ
{"utf8"=>"✓", "authenticity_token"=>"llXh以下略==", "poster_name"=>"", "post_text"=>"", "attachment_name"=>#<ActionDispatch::Http::UploadedFile:0x4dbd910 @tempfile=#<Tempfile:
C:/Users/ユーザー名/AppData/Local/Temp/RackMultipart20171113-6468-19agl2u.png>, @original_filename="detailMain_chihuahua.png", @content_typ

e="image/png", @headers="Content-Disposition: form-data; name="attachment_name"; filename="detailMain_chihuahua.png"\r\nContent-T
ype: image/png\r\n">, "commit"=>"送信", "id"=>"xxxxx"}

コントローラー側
def update
    newrecord = モデル名.new
    newrecord.poster_name = params[:poster_name]
    newrecord.post_text = params[:post_text]
　　###　↓の部分が知りたい
    newrecord.attachment_name = params[:???]

    newrecord.save
    if newrecord.save
      redirect_to controller: 'home', action: 'show'
    else
      render "post/post"
    end
  end

view側
#投稿画面
<%= form_with(model: @userinfo, local: true, html: {id: 'inform_save', class: 'form', autocomplete: 'off'}) do |f| %>
  <div class="field">
    <%= f.label :poster_name, "投稿者名" %>
    <%= f.text_field :poster_name, size: 25, value: "", id: "poster_name", class: "poster_name" %>
  </div>
  <div class="field">
    <%= f.label :post_text, "投稿内容" %>
    <%= f.text_field :post_text, size: 25, value: "", id: "post_text", class: "post_text" %>
  </div>
  <div class="field">
    <%= f.file_field :attachment_name, class: 'attachment_name' %>
  </div>
  <div class="actions">
    <%= f.submit '送信' %>
  </div>
<% end %>

モデル側

#モデル名.rb
class モデル名 < ApplicationRecord
  mount_uploader :attachment_name, ImageUploader
end

#image_uploader.rb
class ImageUploader < CarrierWave::Uploader::Base

  # Include RMagick or MiniMagick support:
  # include CarrierWave::RMagick
  # include CarrierWave::MiniMagick

  # Choose what kind of storage to use for this uploader:
  storage :file
  # storage :fog
  process convert: 'jpg'
  # Override the directory where uploaded files will be stored.
  # This is a sensible default for uploaders that are meant to be mounted:
  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  # Provide a default URL as a default if there hasn't been a file uploaded:
  # def default_url(*args)
  #   # For Rails 3.1+ asset pipeline compatibility:
  #   # ActionController::Base.helpers.asset_path("fallback/" + [version_name, "default.png"].compact.join('_'))
  #
  #   "/images/fallback/" + [version_name, "default.png"].compact.join('_')
  # end

  # Process files as they are uploaded:
  # process scale: [200, 300]
  #
  # def scale(width, height)
  #   # do something
  # end

  # Create different versions of your uploaded files:
  # version :thumb do
  #   process resize_to_fit: [50, 50]
  # end

  # Add a white list of extensions which are allowed to be uploaded.
  # For images you might use something like this:
  def extension_whitelist
    %w(jpg jpeg gif png)
  end

  # Override the filename of the uploaded files:
  # Avoid using model.id or version_name here, see uploader/store.rb for details.
  def filename
    "something.jpg" if original_filename
  end

end