"Rails: NoMethodError for Nested Attributes in Form Submission

Description:

I'm working on a Rails application where I have a Picture model that has a nested Pictureclass model. The index (the gallery of pictures) and the show (a detail of the picture) are showing their category, tipu, and style values. The form for editing/creating also works well, but when I try to create/update a Picture record, I encounter the following error:

NoMethodError in PicturesController#update undefined method `category_id' for an instance of Picture

Controller

class PicturesController < ApplicationController
  before_action :set_picture, only: %i[ show edit update destroy ]

  def index
    @pictures = Picture.where('start_date >= ?', Date.today).order(start_date: :asc)
    @pictureclasses = Pictureclass.where(picture_id: @pictures.pluck(:id)).includes(:category, :ritme, :tipu)
    @categories = @pictureclasses.map(&:category)
    @styles = @pictureclasses.map(&:style)
    @tipus = @pictureclasses.map(&:tipu)
  end

  def show
    @pictureclasses = Pictureclass.where(picture_id: @picture.id).includes(:category, :ritme, :tipu)
    @categories = @pictureclasses.map(&:category)
    @styles = @pictureclasses.map(&:style)
    @tipus = @pictureclasses.map(&:tipu)
  end

  def edit
    @picture = Picture.find_by(slug: params[:id])
    @picture.build_pictureclass if @picture.pictureclass.nil?
    @pictureclasses = Pictureclass.where(picture_id: @picture.id).includes(:category, :ritme, :style)
  end

  def update
    if @picture.update(picture_params)
      redirect_to @picture, notice: "Picture was successfully updated."
    else
      render :edit, status: :unprocessable_entity
    end
  end

  private

  def set_picture
    @picture = Picture.friendly.find(params[:id])
  end

  def picture_params
    params.require(:picture).permit(:start_date, :start_time, :start_point, :title, :descripcio, :ruta_foto, :Km, :slug, :max_inscrits, :min_inscrits, :num_dies, :fi_ndies, :oberta, pictureclass_attributes: [:id, :category_id, :tipu_id, :style_id])
  end
end

Models:

class Picture < ApplicationRecord
  has_one :pictureclass, dependent: :destroy
  accepts_nested_attributes_for :pictureclass, allow_destroy: true
  has_one :category, through: :pictureclass
  has_one :tipu, through: :pictureclass
  has_one :style, through: :pictureclass

end

class Pictureclass < ApplicationRecord
  belongs_to :category
  belongs_to :style
  belongs_to :tipu
  belongs_to :picture
end

class Category < ApplicationRecord
  has_many :pictureclasses, dependent: :destroy
  has_many :pictures, through: :pictureclasses
end

class Tipu < ApplicationRecord
  has_many :pictureclasses, dependent: :destroy
  has_many :pictures, through: :pictureclasses
end

class Style < ApplicationRecord
  has_many :pictureclasses, dependent: :destroy
  has_many :pictures, through: :pictureclasses
end

Form

<%= form_with(model: @picture, class: "contents text-sm") do |form| %>
  <%= form.fields_for :pictureclass do |pictureclass_form| %>
    <div class="field">
      <%= pictureclass_form.label :category_id %>
      <%= pictureclass_form.collection_select :category_id, Category.all, :id, :name %>
    </div>
    <div class="field">
      <%= pictureclass_form.label :tipu_id %>
      <%= pictureclass_form.collection_select :tipu_id, Tipu.all, :id, :name %>
    </div>
    <div class="field">
      <%= pictureclass_form.label :style_id %>
      <%= pictureclass_form.collection_select :style_id, Style.all, :id, :name %>
    </div>
  <% end %>
<% end %>

Steps Taken:

• Ensured that accepts_nested_attributes_for is set up in the Picture model.
• Verified that the form is correctly structured to handle nested attributes.
• Checked that the picture_params method permits the nested attributes.

Question:

What might be causing the NoMethodError for category_id when updating a Picture record, and how can I resolve it?