与 .include 一起使用时，对象不支持 #inspect

Question

所以我遇到了一个我什至不知道如何调试的严重错误。我对 Rails 还很陌生，所以这彻底让我大吃一惊。当我在 Student 的查找中使用 .includes(:school) 时，它返回一个 nilClass 错误，但是当我通过任何其他模型和 .includes(:school) 查找时，School 表现得很好。

class Student < ActiveRecord::Base
    has_many :relationships, foreign_key: "liker_id", dependent: :destroy  
    has_many :matches, foreign_key: "student_1_id", dependent: :destroy  
    belongs_to :school  
    belongs_to :conference  
    belongs_to :would_you_rather  
    belongs_to :hometown  
    belongs_to :year  
    belongs_to :major  
end

class School < ActiveRecord::Base
      belongs_to :conference
      belongs_to :rival, class: "School", foreign_key: "rival_id"
      has_many :students
end

在控制台上

d = Student.where(:id => '1').includes(:school)

SQL 生成

SELECT "schools".* FROM "schools" WHERE "schools"."id" IN (1)

返回错误信息

NoMethodError: undefined method `each' for nil:NilClass
from /.rvm/gems/ruby-2.1.2/gems/activerecord4.1.1/lib/active_record/associations/preloader/association.rb:87:in `block in associated_records_by_owner'
from /.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/associations/preloader/association.rb:86:in `each'
from /.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/associations/preloader/association.rb:86:in `associated_records_by_owner'
from /.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/associations/preloader/singular_association.rb:9:in `preload'
from /.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/associations/preloader/association.rb:20:in `run'
from /.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/associations/preloader.rb:136:in `block (2 levels) in preloaders_for_one'
from /.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/associations/preloader.rb:134:in `each'
from /.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/associations/preloader.rb:134:in `map'
from /.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.1/lib/active_record/associations/preloader.rb:134:in `block in preloaders_for_one'  

在使用 .first 提交查询并使用 .first 执行搜索之前

    d = Student.where(:id => '1').includes(:school)

控制台生成

Student Load (0.6ms)  SELECT "students".* FROM "students"  WHERE "students"."id" = 1  
School Load (0.2ms)  SELECT "schools".* FROM "schools"  WHERE "schools"."id" IN (1)
(Object doesn't support #inspect)  
=> 

并返回一个完全空白的行

我确定错误出在某个地方，我只是不知道如何解决它。我也是 StackOverflow 的新手，所以如果我错过了任何内容，请随时提问。任何帮助表示赞赏。

Answer 1

在students 表中，school_id 列是否定义为string？ Rails 直到最近才喜欢这样。两种选择：

1. 升级到最新版本的 Rails（4.1.4，截至目前）。
2. 将列类型更改为整数（或 UUID）