ruby-on-rails - 从数组中删除时删除 Column_names

Question

如果我做：

name_array = Model.column_names
name_array.delete_if {|name| ["id","created_at","updated_at"].include?(name)}
pp Model.column_names

该命令将返回一个没有, &列名Model.column_names的数组。我的假设是删除名称而不是 Model.column_names 数组。idcreated_atupdated_atname_array

导轨 3.0.13 红宝石 1.9.3

Answer 1

请参阅阵列文档：delete_if

删除块计算为 true 的每个 self 元素。每次调用块时数组都会立即更改，而不是在迭代结束后更改。

因此，当您从中删除元素时name_array，实际上是在从中删除它们，Model.column_names因为它们指向同一事物。

如果您不想这样做，请在删除之前复制数组：

name_array = Model.column_names.dup
name_array.delete_if {|name| ["id","created_at","updated_at"].include?(name)}

Answer 2

你也可以使用拒绝

a = [1,2,3]
a.reject{|x| x>=2}
=> [1]

Answer 3

Dup 可以提供帮助，但需要进行重组。dup 创建“浅拷贝”的事实，它具有以下不明显的后果：

> arr = Model.column_names.dup
=> ["id", "name", "klasse", "cars_count", "klasse_id"] 
> arr.delete('id')
=> "id" 
> arr
=> ["name", "klasse", "cars_count", "klasse_id"] 
> Model.column_names
=> ["id", "name", "klasse", "cars_count", "klasse_id"] 
> arr.each &:upcase!
=> ["NAME", "KLASSE", "CARS_COUNT", "KLASSE_ID"] 
> Model.column_names
=> ["id", "NAME", "KLASSE", "CARS_COUNT", "KLASSE_ID"]