如何基於模型的屬性之一創建或更新模型？ （第5條）

Question

我正在使用Rails 5和PostGres 9.5。 我有一個具有以下領域的模型……

 title             | character varying           | 

我想根據其標題在db / seeds文件中創建或更新模型，這是唯一的約束。 所以我嘗試了

scenario = Scenario.find_or_initialize_by_title(s.title)
scenario.update_attributes(Hash[*@record.attributes.except('created_at','updated_at','id').map { |a| [a.first, nil] }.flatten])

但我收到以下錯誤。 創建或更新模型並排除列出的屬性的正確方法是什么？

localhost:sims nataliab$ rake db:seed
rake aborted!
NoMethodError: undefined method `find_or_initialize_by_title' for #<Class:0x007fb22d28f820>
Did you mean?  find_or_initialize_by
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activerecord-5.0.0.1/lib/active_record/dynamic_matchers.rb:21:in `method_missing'
/Users/nataliab/Documents/workspace/sims/db/seed/scenarios.rb:165:in `block in <top (required)>'
/Users/nataliab/Documents/workspace/sims/db/seed/scenarios.rb:164:in `each'
/Users/nataliab/Documents/workspace/sims/db/seed/scenarios.rb:164:in `<top (required)>'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activesupport-5.0.0.1/lib/active_support/dependencies.rb:293:in `require'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activesupport-5.0.0.1/lib/active_support/dependencies.rb:293:in `block in require'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activesupport-5.0.0.1/lib/active_support/dependencies.rb:259:in `load_dependency'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activesupport-5.0.0.1/lib/active_support/dependencies.rb:293:in `require'
/Users/nataliab/Documents/workspace/sims/db/seeds.rb:10:in `<top (required)>'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activesupport-5.0.0.1/lib/active_support/dependencies.rb:287:in `load'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activesupport-5.0.0.1/lib/active_support/dependencies.rb:287:in `block in load'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activesupport-5.0.0.1/lib/active_support/dependencies.rb:259:in `load_dependency'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activesupport-5.0.0.1/lib/active_support/dependencies.rb:287:in `load'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/railties-5.0.0.1/lib/rails/engine.rb:549:in `load_seed'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activerecord-5.0.0.1/lib/active_record/tasks/database_tasks.rb:268:in `load_seed'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/activerecord-5.0.0.1/lib/active_record/railties/databases.rake:196:in `block (2 levels) in <top (required)>'
/Users/nataliab/.rvm/gems/ruby-2.3.0/gems/rake-11.3.0/exe/rake:27:in `<top (required)>'
/Users/nataliab/.rvm/gems/ruby-2.3.0/bin/ruby_executable_hooks:15:in `eval'
/Users/nataliab/.rvm/gems/ruby-2.3.0/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => db:seed
(See full trace by running task with --trace)

Answer 1

錯誤消息為您提供了線索：

NoMethodError: undefined method `find_or_initialize_by_title' for #<Class:0x007fb22d28f820>
Did you mean?  find_or_initialize_by

現在，動態方法名稱並非真正經過“ Rails批准”，您應該使用find_or_initialize_by 。 在這種情況下，您將使用：

Scenario.find_or_initialize_by(title: s.title)

這是此方法的api文檔的鏈接： http : //apidock.com/rails/v4.0.2/ActiveRecord/Relation/find_or_initialize_by

Answer 2

試試Scenario.find_or_initialize_by(title: s.title)