Question

我收到以下错误：

2.4.1 :001 > Blogger.last
ActiveRecord::IrreversibleOrderError: Relation has no current order and table has no primary key to be used as default order from (irb):1

问题是什么，我该如何解决？

更多信息：

Blogger.first似乎有效：

Blogger.first
Blogger Load (3.6ms)  SELECT  "bloggers".* FROM "bloggers" LIMIT $1  [["LIMIT", 1]]

#<Blogger id: 1, blogger_id: 502, deadline: nil, reminded: nil, needsreminder: nil, created_at: "2018-03-13 12:10:09", updated_at: "2018-03-13 12:10:09", interests: "Ethik, Gesellschaft, Kultur, Logik, Wissen, Wissen...">

博主是用种子创建的：

Blogger.create!([
  {id: 1, blogger_id: 502, deadline: nil, reminded: nil, needsreminder: nil, interests: "Ethik, Gesellschaft, Kultur, Logik, Wissen, Wissenschaft"},
  {id: 2, blogger_id: 453, deadline: nil, reminded: nil, needsreminder: nil, interests: "Ethik, Gesellschaft, Kultur"},
  {id: 3, blogger_id: 434, deadline: nil, reminded: nil, needsreminder: nil, interests: "Menschsein und Sprache"},
  {id: 4, blogger_id: 370, deadline: nil, reminded: nil, needsreminder: nil, interests: "Ethik, Gesellschaft, Kultur"},
  {id: 5, blogger_id: 485, deadline: nil, reminded: nil, needsreminder: nil, interests: "Unbekannt"}
])

以下是Blogger的迁移：

class CreateBloggers < ActiveRecord::Migration[5.1]
  def change
    create_table :bloggers do |t|
      t.integer :blogger_id
      t.date :deadline
      t.date :reminded
      t.boolean :needsreminder

      t.timestamps
    end
  end
end


class AddInterestsToBloggers < ActiveRecord::Migration[5.1]
  def change
    add_column :bloggers, :interests, :string
  end
end

Blogger.rb

class Blogger < ApplicationRecord


end

Rails：5.1.4

Ruby：2.4.1

Postgresql：x86_64-pc-linux-gnu上的PostgreSQL 9.5.12，由gcc编译（Ubuntu 5.4.0-6ubuntu1~16.04.9）5.4.0 20160609,64位

Answer 1

我回滚了我的迁移，然后再次迁移它们。

rails db:rollback
rails db:migrate
rails db:seed

之后，错误不再发生：

2.4.1 :002 > Blogger.last
  Blogger Load (1.5ms)  SELECT  "bloggers".* FROM "bloggers" ORDER BY "bloggers"."id" DESC LIMIT $1  [["LIMIT", 1]]
 => #<Blogger id: 5, blogger_id: 485, deadline: nil, reminded: nil, needsreminder: nil, created_at: "2018-03-13 19:58:33", updated_at: "2018-03-13 19:58:33", interests: "Unbekannt"> 
2.4.1 :003 >

但是，如果有人能解释如果发生这种错误该怎么办，我仍然会很高兴。

Answer 2

我只是重新指定了主键，没有在模型文件中提及任何内容。

注意：我实际上使用现有的表创建了一个新表并出现了这个错误。

我在创建表后在我的迁移文件中指定了以下内容，

execute "ALTER TABLE items ADD PRIMARY KEY (id);"

Rails：如何修复ActiveRecord ::不可逆订单错误

2 个答案: