Rails Create 方法导致 Nil 记录 [英] Rails Create method resulting in Nil records

问题描述

为什么这个 create 方法会创建一个 nil 记录?

Why does this create method make a nil record?

我试过了:

Dropdown.create(主题:测试")

Dropdown.create(subject: "test")

Dropdown.create({subject: "test", subject_value: "1"})

Dropdown.create({subject: "test", subject_value: "1"})

Dropdown.create({:subject => "test", :subject_value => "1"})

Dropdown.create({:subject => "test", :subject_value => "1"})

所有结果为 nil 记录.

   (0.1ms)  begin transaction
  SQL (0.6ms)  INSERT INTO "dropdowns" ("created_at", "updated_at") VALUES (?, ?)  [["created_at", "2016-01-21 23:58:04.979225"], ["updated_at", "2016-01-21 23:58:04.979225"]]
   (2.1ms)  commit transaction
=> #<Dropdown id: 145, subject: nil, visible: nil, subject_value: nil, subject_description: nil, created_at: "2016-01-21 23:58:04", updated_at: "2016-01-21 23:58:04

模型文件

class Dropdown < ActiveRecord::Base
  
    FIELDS =  [
              :subject,
              :visible,
              :subject_value,
              :subject_description
            ]
  
  attr_accessor(*FIELDS)
  subjects = %w[math english spanish]
  
  subjects.each do |s|
    scope s.to_sym, -> { where(subject: s) }
  end

end

迁移文件

class CreateDropdowns < ActiveRecord::Migration
  def change
    create_table :dropdowns do |t|
      t.string :subject
      t.boolean :visible
      t.string :subject_value
      t.string :subject_description

      t.timestamps null: false
    end
  end
end

推荐答案

您通过声明 attr_accessor:

#app/models/dropdown.rb
class Dropdown < ActiveRecord::Base

  subjects = %w(math english spanish)

  subjects.each do |s|
    scope s.to_sym, -> { where(subject: s) }
  end

end

1. 您不需要声明 FIELDS -- 您可以调用 @model.attributes(instance) 或 Model.column_names (class) 以获取该模型的所有字段.

1. You don't need to declare FIELDS -- you can call @model.attributes (instance) or Model.column_names (class) to get all the fields for that model.

attr_accessor 创建一组 getter<类中的/code>/setter 方法.这会覆盖您可能从数据库中拥有的任何属性，这就是为什么您在保存时获得 nil 条目的原因.这里有很好的参考.

attr_accessor creates a set of getter/setter methods in the class. This overrides any attributes you may have from your db, which is why you're getting nil entries when you save. Good ref here.

--

上述模型应该适合您.

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