为什么attr_accessor：type返回nil？

Question

When overriding the to_s method of one of my classes, I'm getting that the field type is nil . I'm positive that it has a not null value. I have a legacy DB so I'm using self.inheritance_column = nil to tell rails not to look for inheritance. This is my class:

class BookEntry < ApplicationRecord
  self.inheritance_column = nil
  attr_accessor :type
  self.table_name = 'bookEntries'
  has_many :users_payout_methods, class_name: 'UsersBooks', primary_key: 'id', foreign_key: 'bookId_fk'
  has_many :users, :through => :users_payout_methods

  def to_s
    "type: "+ type + ", genre:" + genre
  end
end

Other fields, like genre do work properly. Why does this happen?

Answer 1

Remove the line

attr_accessor :type

that basically overrides default Rails getter and setter for a field.

What happens under the hood, is that attr_accessor declares two dummy methods:

def type
  @type
end

def type=(value)
  @type = value
end

Unless you have explicitly set the @type instance variable, it's value is nil since the explicit attr_accessor broke the magic that reads the value from the database field.