[英]Validates uniqueness from foreign key of foreign key
I have 3 models in my rails application, User, Course, and CourseTemplate. 我的Rails应用程序中有3个模型:User,Course和CourseTemplate。
A Course belongs to a User and a CourseTemplate belongs to a Course. 课程属于用户,课程模板属于课程。
What I want to do is to validate the uniqueness between the CourseTemplate name and the User id. 我要做的是验证CourseTemplate名称和用户ID之间的唯一性。
Is this possible? 这可能吗?
class CourseTemplate < ActiveRecord::Base
belongs_to :course
has_one :user, through: :course
validate :unique_course_template_for_user
private
def unique_course_template_for_user
errors.add(:name, 'Must be unique') if CourseTemplate.find_by(user: user.id, name: self.name).count > 0
end
end
If you're ok with some denormalization of your data, you could add user_id
to CourseTemplate, and then simply use the scope feature of validates uniqueness. 如果可以对数据进行一些非规范化,可以将
user_id
添加到CourseTemplate,然后仅使用验证唯一性的范围功能。
Below I show how to use callbacks to maintain the user_id in the CourseTemplate. 下面,我展示了如何使用回调来维护CourseTemplate中的user_id。 Note that it assumes a course cannot be moved to a different user.
请注意,它假定课程不能移至其他用户。
class CourseTemplate < ActiveRecord::Base
before_create :copy_user_id_from_course
validates :name, uniqueness: { scope: :user_id, message: 'Must be unique for the same user'}
private
def copy_user_id_from_course
self.user_id = course.user_id
true
end
end
If the course can be moved to a different user, you should add a callback on Course: 如果可以将课程移至其他用户,则应在课程上添加回调:
class Course < ActiveRecord::Base
after_save :set_course_templates_user, if: :user_id_changed?
private
def set_course_templates_user
course_templates.update_all user_id: self.user_id
end
end
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