Rails Create method resulting in Nil records

问题

Why does this create method make a nil record?

I have tried:

Dropdown.create(subject: "test")

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

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

All result in nil records.

   (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

Model file

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

Migration file

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

回答1:

You're overriding your ActiveRecord::Base functionality by declaring 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

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 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.

The above model should work for you.

回答2:

It is not necessary to use attr_accessor if these fields are columns of a table in your database. ActiveRecord done it for you.

Try to use attr_accessible instead of attr_accessor. But for rails 4+, not necessary to use it. see http://apidock.com/rails/ActiveModel/MassAssignmentSecurity/ClassMethods/attr_accessible

This method is deprecated or moved on the latest stable version. The last existing version (v3.2.13) is shown here.

来源：https://stackoverflow.com/questions/34937935/rails-create-method-resulting-in-nil-records

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ruby-on-rails

ruby

ruby-on-rails-4