所以我遇到了一个令人讨厌的错误,我什至不知道如何调试。我对 Rails 还很陌生,所以这彻底让我大吃一惊。当我在 Student 查找中使用 .includes(:school)
时,它会返回 nilClass 错误,但是当我通过任何其他模型查找时 .includes(:school)
code>,学校表现很好。
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
d = Student.where(:id => '1').includes(:school)
生成 SQL
SELECT "schools".* FROM "schools" WHERE "schools"."id" IN (1)
返回错误消息
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 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
我确信错误就在某个地方,我只是不知道如何解决它。我也是 StackOverflow 的新手,所以如果我错过了什么,请随时询问。如有任何帮助,我们将不胜感激。
最佳答案
在students
表中,school_id
列是否定义为string
? Rails 直到最近才喜欢这样。两个选项:
- 升级到最新版本的 Rails(截至目前
4.1.4
)。 - 将列类型更改为整数(或 UUID)
关于ruby-on-rails - 与 .include 一起使用时,对象不支持 #inspect,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/24981092/