问题描述
使用以下代码在后台会发生什么?
What happens in the background with the following code?
class User < ActiveRecord::Base
attr_accessor :name
attr_accessible :name
end
提示:实例化该类时，它将持久化到数据库中吗?为什么或为什么不呢?
Hint: When instantiating the class, will it be persisted to the database? Why or why not?
推荐答案
感谢大家的快速解答！我认为，您的回答加在一起，为我提供了理解此难题所需的知识.
Thanks everyone for quick answers!Your answers combined gave me the pieces I needed to understand this puzzle, I think.
(在一个相关的问题中，我遇到了很多nil错误，例如对象不支持#inspect"和"nil:NilClass的未定义方法'keys".共有att_accessor字段.)
(In a related problem, I was getting a lot of nil errors like "Object doesn’t support #inspect", and "undefined method ‘keys’ for nil:NilClass". I managed to solve it now, by removing the att_accessor field altogether.)
通过试验这种特殊情况，这是我发现的:
By experimenting with this particular case, this is what I've found out:
实际上，:name字段不会保留到数据库中.
Actually, the :name field won't be persisted to the database.
user = User.new(:name=>"somename")
将仅在对象上设置属性，而不会将:name列保留到数据库中.就像下面的"rails console"输出所示:
Will only set the attribute on the object, but not persist the :name column to the database. Like the following 'rails console' output shows:
> user
=> <User id: nil, created_at: nil, updated_at: nil>
> user.save
=> true
> user
=> <User id:1, created_at: 2011-01-19 12:37:21, updated_at: 2011-01-19 12:37:21>
我认为这是因为* attr_accessor所做的设置器将覆盖ActiveRecord的设置器*(这将照顾数据库的持久性).您仍然可以从对象的:name字段中检索值，如下所示:
I assume this is because *the setter made by attr_accessor will override ActiveRecord's setter* (which takes care of the database persistence). You can still retrieve the value from the :name field from the object though, like this:
> user.name
=> "somename"
因此，总而言之，我了解到在字段上使用attr_accessor可能导致它们无法持久保存到数据库中.虽然我认为attr_accessible描述了应该从外部访问的数据库中的字段，但在这种情况下似乎没有什么不同.
So, in conclusion, I've learnt that using attr_accessor on fields might lead to them not being persisted to the database. And while I thought attr_accessible describes fields in the database that should be accessible from the outside, it doesn't seem to make a difference in this case.
这篇关于在同一字段上使用attr_accessor和attr_accessible的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！