Rails Ancestry gem:确保在保存节点时存在父节点

Question

我今天第一次尝试将Ancestry gem作为内容管理系统的一部分，并希望能够手动创建节点并将它们连接到树中。换句话说，上下文并没有规定任何新节点的父节点是什么，这与每个人都读过的许多线程讨论示例不同。

目前，当我试图保存（创建或更新）一个parent_id不存在（"4"）的节点时，我得到了错误：

ActiveRecord::RecordNotFound in TreesController#update
Couldn't find Tree with 'id'=4

我希望将引用不存在的父节点的任何节点指定为没有父节点。我该怎么做？

这是trees_controller.rb:的相关部分

  def create
    @tree = Tree.new(tree_params)
    if @tree.save
        redirect_to trees_url, notice: "Tree was successfully created"
    else
        render :new
    end     
  end
  ...
  private
  def tree_params
    params.require(:tree).permit(:name, :value, :note, :parent_id)
  end

感谢

Answer 1

经过一周的研究，我终于把它整理好了。以下是针对那些遇到相同障碍的人的解决方案：

  def create
    parent_exists = Tree.exists?(params[:tree][:parent_id])
    if !parent_exists
        params[:tree][:parent_id] = nil
        note = "Parent node didn't exist so set to nil."
    end
    @tree = Tree.new(tree_params)
    if @tree.save
        redirect_to trees_url, notice: "Node was successfully created. " + note.to_s
    else
        render :new, notice: "There was an error saving this node. Please try again."
    end
  end