You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: rdb_category_filter.rb
    path of file: ./repos/redmine_dashboard/app/models
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class RdbCategoryFilter < RdbFilter
  def initialize
    super :category
  end

  def scope(scope)
    return scope if all?

    scope.where category_id:
    
  def update(params)
    return unless (category = params[:category])

    if category == 'all'
      self.values = board.issue_categories.pluck(:id)
    else
      id = category.to_i

      if params[:only]
        self.value = id
      elsif values.include?(id) && values.count > 2
        values.delete id
      elsif valid_value?(id)
        values << id
      end