Ruby变量似乎为nil但不是nil

Question

I get the error undefined method '[]' for nil:NilClass at the marked line. The logger shows that hash in not nil. It seems I don't call this method on anyhing else in that line. What am I missing here?

def initialize(hash)
    Rails.logger.debug "Attr init hash: #{hash.inspect}, nil?: #{hash.nil?}"
    self.name = hash[:name] #error here
    self.type = hash[:type]
    self.default_value = hash[:default_value]
    self.original_name = if hash[:original_name]
                           hash[:original_name]
                         else
                           name
                         end
  end

This is the output of the logger:

Attr init asdasd: {:name=>"join_id.alma", :type=>"", :default_value=>"", :original_name=>nil}, nil?: false

Answer 1

You overrode initialize and therefore your ActiveRecord object wasn't initialized correctly. The error is raised because self.name internally tried to update the instance's attributes hash and fails.

When you override the initialize method it makes sense to call super to run the default initialize method first:

def initialize(hash)
  super(hash.slice(:name, :type, :default_value))
  self.original_name = hash[original_name] || name
end