无法将 nil 转换为确切的数字

Posted 2023-02-15

【中文标题】无法将 nil 转换为确切的数字

【英文标题】：can't convert nil into an exact number

【发布时间】：2013-01-15 14:00:26

【问题描述】：

我希望用户能够评论其他人的微博，但我不断收到以下错误：

它来自下面 View/cmets/_form 文件中的时间戳。出于某种原因，@comment.created_at 返回为 nil

View/cmets/_form:(这个partial在每条微博结束时调用）

<span class="content"><%= @comment.content %></span>
<span class="timestamp">Said <%= time_ago_in_words(@comment.created_at) %> ago.</span
<%= form_for(@comment) do |f| %>
  <%= f.text_field :content, placeholder: "Say Something..." if signed_in? %>
<% end %>

用户模型：

attr_accessible :name, :email, :password, :password_confirmation #is this secure with password there?
attr_protected :admin   #attr_protected necessary?
has_many :microposts, dependent: :destroy
has_many :comments, :through => :microposts, dependent: :destroy

微博模型：

attr_accessible :comment #basically the content of the post
attr_protected :user_id
has_many :comments, dependent: :destroy

评论模型：

attr_accessible :content, :micropost
belongs_to :user
belongs_to :micropost
validates :user_id, presence: true
validates :micropost_id, presence: true
validates :content, presence: true
default_scope order: 'comments.created_at ASC'   #is this necessary?

评论控制器：

def create
  @micropost = Micropost.find_by_id(params[:id])   #is this necessary?
  @comment = current_user.comments.create(:micropost => @micropost)
  redirect_to :back
end

用户控制器：

def show
  @user = User.find_by_id(params[:id])
  @microposts = @user.microposts.paginate(page: params[:page])
  @micropost  = current_user.microposts.build
  @comments = @micropost.comments
  @comment = current_user.comments.create(:micropost => @micropost) #build, new or create??
end

路线：

resources :users 
resources :microposts, only: [:create, :destroy] 
resources :comments, only: [:create, :destroy]

SQL：

“评论”=>“内容”=>“示例” 用户负载 (0.8ms) SELECT "users".* FROM "users" WHERE "users"."remember_token" = 'H09yZpAv5qhmT3ok5fXfnQ' LIMIT 1 Micropost Load (0.7ms) SELECT "microposts".* FROM "microposts" WHERE "microposts"."id" IS NULL

【参考方案1】：

@comment 很可能是一条将created_at 设置为nil 的新记录

【参考方案2】：

@micropost 尚未创建

在@micropost = current_user.microposts.build之后添加@micropost.save

@micropost  = current_user.microposts.build
@micropost.save
@comments = @micropost.comments
@comment = current_user.comments.create(:micropost => @micropost)

【讨论】：

如果在bluid之后添加save，为什么不直接调用create呢？

这是 SQL 说我想要 null micropost id？ "comment"=>"content"=>"EXAMPLE" 用户负载 (0.8ms) SELECT "users".* FROM "users" WHERE "users"."remember_token" = 'H09yZpAv5qhmT3ok5fXfnQ' LIMIT 1 Micropost Load (0.7 ms) SELECT "microposts".* FROM "microposts" WHERE "microposts"."id" IS NULL