Rails：多对多关系 - 创建和关联新记录

Question

我将此 railscast #17 revised 视为使用连接在两个模型之间创建多对多关系的教程 table:

class Course < ActiveRecord::Base
has_many :courselocalizations
has_many :courselocations, through: :courselocalizations
end

class Courselocation < ActiveRecord::Base
has_many :courselocalizations
has_many :courses, through: :courselocalizations
end

class Courselocalization < ActiveRecord::Base
belongs_to :course
belongs_to :courselocation
end

如果用户在编辑或创建 course 时没有看到现有的 courselocation，他们创建新 courselocation 并自动建立关联的最佳方式是什么？

Answer 1

您可以分两步完成（我的首选方法），也可以一步完成。

2步过程： - 创建 CourseLocation - 关联 CourseLocation 和 Course。

course_location1 = CourseLocation.create(name: 'location1')
course.course_locations << course_location1

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如果您想一步完成，可以使用 Active Record accepts_nested_attributes_for method, this is a little tricky. Here is a good article，但让我们分解这些步骤：

1. 课程需要接受 course_localizations
的属性
2. 课程本地化需要接受 course_location
的属性
3. 创建课程时，传递包含位置属性的本地化属性。

让我们针对您的特定情况进行设置：

class Course < ActiveRecord::Base
  # attribute subject
  has_many :course_localizations, inverse_of: :course
  has_many :course_locations, through: :course_localizations
  accepts_nested_attributes_for :course_localizations
end

class CourseLocation < ActiveRecord::Base
  # attribute city
  has_many :course_localizations
  has_many :courses, through: :course_localizations
end

class CourseLocalization < ActiveRecord::Base
  belongs_to :course
  belongs_to :course_location
  accepts_nested_attributes_for :course_locations
end

此时你应该可以

course = Course.new(
  subject: "Math",
  course_localizations_attributes: [
    { course_location_attributes: { city: "Los Angeles" } },
    { course_location_attributes: { city: "San Francisco" } }]
)

course.save