Mongoid-tree：爲什麼我只在Node.new上獲取子數組而不是Node.create？

Question

可正常工作：

[1] consum » node = Node.new(name: "p") 
=> #<Node:0x007ff032b941d0> { 
     :_id => "51e88c41c7e9680108000001", 
     :name => "p", 
    :parent_ids => [], 
    :repeated => false 
} 
[2] consum » node.children 
=> [] 

這不：

[3] consum » node = Node.create(name: "p") 
=> #<Node:0x007ff03250a6c0> { 
     :_id => "51e88c4dc7e9680108000002", 
    :created_at => 2013-07-19 00:46:05 UTC, 
     :name => "p", 
    :parent_ids => [], 
    :repeated => false, 
    :updated_at => 2013-07-19 00:46:05 UTC 
} 
[4] consum » node.children 
=> nil 

Answer 1

我相信這是因爲Node.new產生具有同時Node.create空數組節點對象的實例的實例的表示的一個新節點實際上堅持到數據庫（大概是用空陣列跳過字段）