funkos.rb

class Funko
  # Add these scopes to your model
  scope :for_user, ->(user) { where(user: user) }
  scope :for_category, ->(category) { joins(:category).where(categories: { name: category }) }
  scope :newest, -> { order(created_at: :desc) }
end

def index
  category = params[:category]
  @funkos = Funko.newest
  @funkos = @funkos.for_user(current_user) if user_signed_in?
  @funkos = @funkos.for_category(category) if category.present?
end