How do I force ActiveRecord to reload a class?

Question

I'm creating a bunch of migrations, some of which are standard "create table" or "modify table" migrations, and some of which modify data. I'm using my actual ActiveRecord models to modify the data, a la:

Blog.all.each do |blog|
  update_some_blog_attributes_to_match_new_schema
end

The problem is that if I load the Blog class, then modify the table, then use the Blog class again, the models have the old table definitions, and cannot save to the new table. Is there a way to reload the classes and their attribute definitions so I can reuse them?

score 143 · Accepted Answer · answered Oct 14 '08 at 11:41

143

The answer is yes!

Blog.reset_column_information

answered Oct 14 '08 at 11:41

James A. Rosen

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2

Watch out for models with relationships. If `class Blog; belongs_to Owner; end`, then you may need to `Owner.reset_column_information` in addition to Blog. – Gavin Brock Jun 05 '12 at 05:33
4

Reset all the columns! `ActiveRecord::Base.descendants.each{|c| c.reset_column_information}` – rude-n8 Jul 09 '14 at 00:33
1

Throw `Rails.application.eager_load!` in front of any calls to descendants to fix issues with non-autoloaded models – elju Nov 25 '15 at 15:30
I wonder why this is not triggered automatically after every schema update, since migrations are not very time-critical. – juffel May 04 '16 at 14:04

score 5 · Answer 2 · answered Oct 14 '08 at 16:30

I always used new models in migrations

    MyBlog < ActiveRecord::Base
      set_table_name 'blogs'
    end

    def self.up
      MyBlog.all.each do |blog|
        update_some_blog_attributes_to_match_new_schema
      end
    end

But Blog.reset_column_information is more convenient.

score 3 · Answer 3 · edited Oct 21 '16 at 09:57

3

Create new instances:

Old_blogs = Blog.all

# change/modify db table in here

New_blogs = Blog.all # this should be reloaded or you could use the .reload on this

# change information, load old into new

ex.

Old_blogs.each do |blog|
  New_blogs.find(blog.id).title = blog.title
end

edited Oct 21 '16 at 09:57

rohin-arka

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answered Oct 14 '08 at 12:09

Jon Smock

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How do I force ActiveRecord to reload a class?

3 Answers3

ex.

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