我试图用公文包保存技术的嵌套属性，我有以下代码：portfolio.rb(模型(
class Portfolio < ApplicationRecord
has_many :technologies
# do not accept the insertion if name is blank
accepts_nested_attributes_for :technologies,
reject_if: lambda{ |attrs| attrs['name'].blank? }
validates_presence_of :title, :body, :main_image, :thumb_image
include Placeholder
validates_presence_of :title, :body, :main_image, :thumb_image
# class method - custom scope
def self.angulars
where(subtitle: "Angular")
end
# lambda - custom scope
scope :ruby_on_rails_p_items, -> { where(subtitle: "Ruby on Rails") }
# callbackss
after_initialize :set_defaults
def set_defaults
self.main_image ||= Placeholder.image_generator(height:'600', width:'400')
self.thumb_image ||= Placeholder.image_generator(height:'350', width:'200')
end
end
technology.rb模型：
class Technology < ApplicationRecord
belongs_to :portfolio
end
现在，当我转到rails控制台并尝试插入多个属性时：
Portfolio.create!(title: "Web App", subtitle: "asadasd", body: "sadsadas", technologies_attributes: [{name: "Ruby"}, {name: "Rails"}, {name: "Angula"}, {name: "Ionic"}])
它给了我一个错误：
ActiveRecord::RecordInvalid: Validation failed: Technologies portfolio must exist
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/validations.rb:78:in `raise_validation_error'
知道我在这里错过了什么吗？
技术和产品组合的模式：
create_table "portfolios", force: :cascade do |t|
t.string "title"
t.string "subtitle"
t.text "body"
t.text "main_image"
t.text "thumb_image"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "technologies", force: :cascade do |t|
t.string "name"
t.integer "portfolio_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.index ["portfolio_id"], name: "index_technologies_on_portfolio_id", using: :btree
end
完整错误消息：
ActiveRecord::RecordInvalid: Validation failed: Technologies portfolio must exist
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/validations.rb:78:in `raise_validation_error'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/validations.rb:50:in `save!'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/attribute_methods/dirty.rb:30:in `save!'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/transactions.rb:324:in `block in save!'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/transactions.rb:395:in `block in with_transaction_returning_status'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/connection_adapters/abstract/database_statements.rb:232:in `block in transaction'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/connection_adapters/abstract/transaction.rb:189:in `within_new_transaction'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/connection_adapters/abstract/database_statements.rb:232:in `transaction'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/transactions.rb:211:in `transaction'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/transactions.rb:392:in `with_transaction_returning_status'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/transactions.rb:324:in `save!'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/suppressor.rb:45:in `save!'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activerecord-5.0.7/lib/active_record/persistence.rb:51:in `create!'
from (irb):3
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/railties-5.0.7/lib/rails/commands/console.rb:65:in `start'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/railties-5.0.7/lib/rails/commands/console_helper.rb:9:in `start'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/railties-5.0.7/lib/rails/commands/commands_tasks.rb:78:in `console'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/railties-5.0.7/lib/rails/commands/commands_tasks.rb:49:in `run_command!'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/railties-5.0.7/lib/rails/commands.rb:18:in `<top (required)>'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activesupport-5.0.7/lib/active_support/dependencies.rb:293:in `require'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activesupport-5.0.7/lib/active_support/dependencies.rb:293:in `block in require'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activesupport-5.0.7/lib/active_support/dependencies.rb:259:in `load_dependency'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activesupport-5.0.7/lib/active_support/dependencies.rb:293:in `require'
from /Users/mac/Desktop/DevCampPortfolio/bin/rails:9:in `<top (required)>'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activesupport-5.0.7/lib/active_support/dependencies.rb:287:in `load'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activesupport-5.0.7/lib/active_support/dependencies.rb:287:in `block in load'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activesupport-5.0.7/lib/active_support/dependencies.rb:259:in `load_dependency'
from /Users/mac/.rvm/gems/ruby-2.3.1/gems/activesupport-5.0.7/lib/active_support/dependencies.rb:287:in `load'
from /Users/mac/.rvm/rubies/ruby-2.3.1/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /Users/mac/.rvm/rubies/ruby-2.3.1/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from -e:1:in `<main>'
2.3.1 :004 > Portfolio.create!(title: "Web App", subtitle: "asadasd", body: "sadsadas", main_image: 'some value', thumb_image: 'some image')
将belongs_to :portfolio关联设置为可选并不能解决问题。通过传递optional: true所做的只是跳过验证，如果您真的想设置一个具有模型关联的数据库模式，那么这是没有用的。
问题的根本原因是Active Record试图在Portfolio对象提交到数据库之前创建Technology对象。accepts_nested_attributes_for的特殊之处在于它通过父模型(Portfolio(创建关联模型(在本例中为Technology(的实例。为此，Active Record需要了解两个模型之间的关系，并且它还必须有一个外键来将关联的Technology对象绑定到特定的Portfolio。
如果您先创建一个Portfolio对象，然后单独创建一个Technology对象，您就不会有问题：
portfolio = Portfolio.create!(title: "Web App", subtitle: "asadasd", body: "sadsadas")
Technology.create!(name: 'aoeifjeao', portfolio_id: portfolio.id)
=> #<Technology id: 10, name: "aoeifjeao", portfolio_id: 17, created_at: "2019-12-07 03:54:47", updated_at: "2019-12-07 03:54:47">
如果您检查由Technology.create代码生成的SQL查询，那么这一操作的原因就很清楚了：
(0.4ms) BEGIN
Portfolio Load (0.7ms) SELECT "portfolios".* FROM "portfolios" WHERE "portfolios"."id" = $1 LIMIT $2 [["id", 17], ["LIMIT", 1]]
SQL (1.6ms) INSERT INTO "technologies" ("name", "portfolio_id", "created_at", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id" [["name", "aoeifjeao"], ["portfolio_id", 17], ["created_at", "2019-12-07 03:54:47.668662"], ["updated_at", "2019-12-07 03:54:47.668662"]]
(41.0ms) COMMIT
注意，发生的第一件事是Active Record从具有特定id的数据库中查找Portfolio。然后，它将具有相同portfolio_id的新记录插入到technologies表中。
当您使用活动记录创建具有关联的模型时，就会发生这种情况。它首先使用您指定的id在数据库中查找父模型，然后将其作为子模型的外键。
回到您的代码，当您调用Portfolio.create时，您实际上要做的是创建父对象和子对象，并设置它们的关联，所有这些都是在任何记录保存到数据库之前完成的。
实际发生的是Portfolio.create被分解为两个步骤。调用第一个Portfolio.new，它实例化(但不保存(Portfolio对象：
portfolio = Portfolio.new(title: "Web App", subtitle: "asadasd", body: "sadsadas", technologies_attributes: [{name: "Ruby"}])
=> #<Portfolio id: nil, title: "Web App", subtitle: "asadasd", body: "sadsadas", main_image: "http://placehold.it/600x400", thumb_image: "http://placehold.it/350x200", created_at: nil, updated_at: nil>
注意，我们的嵌套属性已经用于通过Portfolio关联实例化Technology对象，但外键portofolio_id是nil:
portfolio.technologies
=> #<ActiveRecord::Associations::CollectionProxy [#<Technology id: nil, name: "Ruby", portfolio_id: nil, created_at: nil, updated_at: nil>]>
接下来，调用Portfolio.save，抛出ActiveRecord::RecordInvalid验证错误。这说明Technology对象需要一个Portfolio关联，但它没有，因为portfolio_id仍然是nil。
当设置belongs_to和has_many关系时，Active Record会尝试基于启发式方法自动猜测反向关联，通常是通过查看表名。它通常非常擅长，但有时需要显式地声明两个模型之间的inverse_of关系。
# portfolio.rb
class Portfolio < ApplicationRecord
has_many :technologies, inverse_of: :portfolio
end
# technology.rb
class Technology < ApplicationRecord
belongs_to :portfolio, inverse_of: :technologies
end
您在Portfolio上进行了验证
validates_presence_of :title, :body, :main_image, :thumb_image
你只通过了:title, :subtile, :body，而没有通过:main_image, :thumb_image
Portfolio.create!(title: "Web App", subtitle: "asadasd", body: "sadsadas", technologies_attributes: [{name: "Ruby"}, {name: "Rails"}, {name: "Angula"}, {name: "Ionic"}])
上面的代码期望保存Portfolio应该是成功的，所以它可以在Technology中使用portfolio_id，但这里没有发生这种情况，您需要将所有必需的参数传递给Portfolio.create!
Portfolio.create!(title: "Web App", subtitle: "asadasd", body: "sadsadas", main_image: 'some value', thumb_image: 'some image',
technologies_attributes: [{name: "Ruby"}, {name: "Rails"}, {name: "Angula"}, {name: "Ionic"}])
更新：
当您使用Rails 5.x时，在Rails5.x(以后(中，所有belongs_to关联都会默认验证(belongs_to-association(存在性为true，请将optional: true添加到您的技术模型中。阅读有关此的更多信息
class Technology < ApplicationRecord
belongs_to :portfolio, optional: true
end