Mongoid 无法保存具有 belongs_to/has_many 关系的文档。循环依赖

Question

我有 2 个 Mongoid 类：

class Reservation
  include Mongoid::Document
  belongs_to :listing, class_name: 'Listing', inverse_of: 'Reservation'
end

class Listing
  include Mongoid::Document
  has_many :reservations, class_name: 'Reservation', foreign_key: :listing_id
end

如果我通过_id 和#save! 找到列表，则不会出现错误

listing = Listing.find(...)
listing.save! #=> true

然后我初始化一个新的预订对象：

reservation = Reservation.find_or_initialize_by(params)
reservation.save! #=> error, exptected though, because I didn't set the listing_id yet

Mongoid::Errors::Validations: 
message:
  Validation of Reservation failed.
summary:
  The following errors were found: Listing can't be blank
resolution:
  Try persisting the document with valid data or remove the validations.
from /home/ec2-user/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/bundler/gems/mongoid-71c29a805990/lib/mongoid/persistable.rb:78:in `fail_due_to_validation!'

所以我将较早的房源的 id 分配给预订：

reservation.listing_id = listing._id
reservation.listing_id #=> nil

我什至不能分配listing_id 字段？！

reservation.listing    #=> returns the associated document no problem though..
reservation.listing.save! #=> error

Mongoid::Errors::Validations: 
message:
  Validation of Listing failed.
summary:
  The following errors were found: Reservations is invalid
resolution:
  Try persisting the document with valid data or remove the validations.
from /home/ec2-user/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/bundler/gems/mongoid-71c29a805990/lib/mongoid/persistable.rb:78:in `fail_due_to_validation!'

如果没有有效的列表，无法保存预订， 没有有效预订，无法保存房源

这是什么？！？！

请拯救我的一天...

Answer 1

您实际上必须在 inverse_of 中指定反向字段，因此请尝试以下内容：

class Reservation
  include Mongoid::Document
  belongs_to :listing, class_name: 'Listing', inverse_of: :reservations
end

class Listing
  include Mongoid::Document
  has_many :reservations, class_name: 'Reservation', inverse_of :listing
end

我还用inverse_of替换了has_many关系的foreign_key，这样更容易让Mongoid猜测外键名:)

然后，检查您指定的验证并且您没有包含在您的帖子中，但是如果您首先创建一个列表，您应该能够毫无问题地为其创建预订。

另外，直接分配对象也可以，而且通常更容易，所以你可以直接写reservation.listing = my_listing