无效参数:升级到Rails 5后无错误

Question

我升级到了Rails5，在启动服务器之后，必须加载登录表单。则会出现以下错误：

ArgumentError - invalid argument: nil.:
  activerecord (5.0.0.1) lib/active_record/relation/spawn_methods.rb:36:in `merge'
  activerecord (5.0.0.1) lib/active_record/scoping/default.rb:119:in `block (2 levels) in build_default_scope'
  activerecord (5.0.0.1) lib/active_record/scoping/default.rb:117:in `block in build_default_scope'
  activerecord (5.0.0.1) lib/active_record/scoping/default.rb:141:in `evaluate_default_scope'
  activerecord (5.0.0.1) lib/active_record/scoping/default.rb:116:in `build_default_scope'
  activerecord (5.0.0.1) lib/active_record/scoping/named.rb:33:in `default_scoped'
  activerecord (5.0.0.1) lib/active_record/scoping/named.rb:28:in `all'
  activerecord (5.0.0.1) lib/active_record/scoping.rb:24:in `scope_attributes'
  activerecord (5.0.0.1) lib/active_record/scoping.rb:36:in `populate_with_current_scope_attributes'
  activerecord (5.0.0.1) lib/active_record/scoping.rb:43:in `initialize_internals_callback'
  activerecord (5.0.0.1) lib/active_record/core.rb:317:in `initialize'
  activerecord (5.0.0.1) lib/active_record/inheritance.rb:65:in `new'
  devise (4.2.0) app/controllers/devise/sessions_controller.rb:9:in `new'

我想这似乎是来自于Devise？在搜索之后，我发现有人出现了同样的错误：

Turns it it was a gem which behind the scenes was attempting to do default_scope { nil }, looks like someone implemented protection against that (since it shouldn't really work)

我该怎么办？

Answer 1

nil作为merge参数不再有效，因为该方法需要ActiveRecord_Relation类的参数。

此问题与this PR on Rails相关。这是resolution commit on rails。

要避免此错误，请执行以下操作：

• 在对关系调用merge属性之前检查它，并且仅当它不为空时才追加它。
• 或始终将有效的ActiveRecord_Relation传递给merge，例如，如果实际参数为nil，则使用<ARModel>.all代替nil。