ActiveRecord::Relation 的未定义方法 [英] undefined method for ActiveRecord::Relation

问题描述

用户模型

class User < ActiveRecord::Base
  has_many :medicalhistory 
end

医学历史模型

class Medicalhistory < ActiveRecord::Base
  belongs_to :user #foreign key -> user_id
  accepts_nested_attributes_for :user
end

错误

undefined method `lastname' for #<ActiveRecord::Relation:0xb6ad89d0>


#this works
@medicalhistory = Medicalhistory.find(current_user.id) 
print   "
" + @medicalhistory.lastname

#this doesn't!
@medicalhistory = Medicalhistory.where("user_id = ?", current_user.id)
print   "
" + @medicalhistory.lastname #error on this line

推荐答案

好吧，您正在返回 ActiveRecord::Relation 的对象，而不是您的模型实例，因此错误，因为没有ActiveRecord::Relation 中名为 lastname 的方法.

Well, you are getting back an object of ActiveRecord::Relation, not your model instance, thus the error since there is no method called lastname in ActiveRecord::Relation.

执行@medicalhistory.first.lastname 有效，因为@medicalhistory.first 正在返回由where.

Doing @medicalhistory.first.lastname works because @medicalhistory.first is returning the first instance of the model that was found by the where.

此外，您可以打印出@medicalhistory.class 的工作代码和错误"代码，看看它们有何不同.

Also, you can print out @medicalhistory.class for both the working and "erroring" code and see how they are different.

这篇关于ActiveRecord::Relation 的未定义方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！