如何通过反射获得 activerecord 关联 [英] How to get activerecord associations via reflection

问题描述

对于普通列，您可以通过 columns 类方法获取它们.但是，如果在关系方法中设置了 foreign_key 选项，则关联可能会被命名为完全不同的名称.例如，给定

For normal columns, you can get at them via the columns class method. However, associations may be named something quite different if the foreign_key option is set in the relationship method. For example, given

class Post
  has_many :comments, :foreign_key => :message_id # this is a contrived example
end

如果我做了Post.column_names，我可以得到message_id，但是有没有办法得到comments?

if I did Post.column_names I could get at message_id, but is there any way to get comments?

推荐答案

Model.reflections 提供有关模型关联的信息.它是一个以关联名称为键的 Hash.例如

Model.reflections gives information about a model's associations. It is a Hash keyed on the association name. e.g.

Post.reflections.keys # => ["comments"]

以下是它可以用来访问的一些信息的示例:

Here is an example of some of the information it can be used to access:

Post.reflections["comments"].table_name # => "comments"
Post.reflections["comments"].macro # => :has_many
Post.reflections["comments"].foreign_key # => "message_id"

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注意:此答案已更新以涵盖基于 MCB 的 Rails 4.2回答和下面的评论.在早期版本的 Rails 中，反射的 foreign_key 是使用 primary_key_name 访问的，反射的键可能是符号而不是字符串，这取决于关联的定义方式，例如:comments 而不是 "comments".

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Note: this answer has been updated to cover Rails 4.2 based on MCB's answer and the comments below. In earlier versions of Rails the reflection's foreign_key was accessed using primary_key_name instead, and the keys for the reflections may be symbols instead of strings depending on how the association was defined e.g. :comments instead of "comments".

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