Rails db:migrate关系不存在
我有这样的模特:
学生:
class Student < ActiveRecord::Base has_many :participations, dependent: :destroy has_many :subject_item_notes, dependent: :destroy has_many :payments, dependent: :destroy has_many :subject_items, dependent: :destroy, through: :participations has_many :subject_items, dependent: :destroy validates :first_name, :last_name, presence: true accepts_nested_attributes_for :subject_items end
和subject_item:
class SubjectItem (teacher) { where('teacher_id IS ? or teacher_id = ?', nil, teacher) } end
和迁移:
class AddStudentToSubjectItems < ActiveRecord::Migration def change add_reference :subject_items, :student, index: true end end
但是当我做rake db:migrate
我收到错误:
== 20151121045103 AddStudentToSubjectItems: migrating ========================= -- add_reference(:subject_items, :student, {:index=>true}) rake aborted! StandardError: An error has occurred, this and all later migrations canceled: PG::UndefinedTable: ERROR: relation "subject_items" does not exist : ALTER TABLE "subject_items" ADD "student_id"
在恐慌中我多次重建数据库并且在架构中发生了一些混乱…… 🙁
至于现在我试着做:
rake db:drop然后rake db:create和rake db:migrate,然后出现此错误。
首先,检查您的迁移顺序。 在创建表subject_items
本身之前,您似乎正在尝试创建引用。
您应首先创建学生表,然后创建您的subject_items表,然后添加参考。 或者在创建表时自己添加引用列,这就是add_reference
所做的 。
此外,您有两个从Student
到SubjectItem
关系。
has_many :subject_items, dependent: :destroy, through: :participations has_many :subject_items, dependent: :destroy
您需要建立第一个关系,以便ActiveRecord能够首先识别正确的关系,然后进行查询以进行迁移。 想想如果你打电话给@student.subject_items
就会生成的查询。 它会通过第一个关系还是第二个关系。
你的关系应该是ex:
has_many :participation_subject_items, dependent: :destroy, through: :participations has_many :subject_items, dependent: :destroy