#6234 Request for automatic invocation of 'reset_column_information' in Migrations - Ruby on Rails

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#6234 open

Request for automatic invocation of 'reset_column_information' in Migrations

Reported by Ivo Wever | December 30th, 2010 @ 03:52 PM

Short version: please run Model.reset_column_information after running a Migration.

Long version:
I just spent quite some time hunting for the fact that if you do

class ModifyModel < ActiveRecord::Migration
  def self.up
    add_column :model, :some_column, :string
    p Model.columns
  end
end

the column you just added won't show up and for all practical purposes doesn't exist. You need to issue a

Model.reset_column_information

to get access to the column. This causes problems when, for instance, a rake task is used to recreate a certain default database situation and consists of running migrations and doing seeding afterwards. I'm sure I'm not the only one that ran into this issue and it could be prevented/fixed by always running 'reset_column_information' after a Migration, which sounds very sensible to me. I would say it at least violates the principle of least surprise that adding a column to a Model does not actually result in that column being available.

Comments and changes to this ticket

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Joshua Pinter January 4th, 2011 @ 07:39 PM
I concur. Just ran into this myself.

Spent a few hours hunting it down and another hour making updates to my migrations.

Oscar Del Ben January 5th, 2011 @ 09:17 AM

In the rails test suite, there is a test where they specifically call reset_column_information:

def test_native_types
      Person.delete_all
      Person.connection.add_column "people", "last_name", :string
      Person.connection.add_column "people", "bio", :text
      Person.connection.add_column "people", "age", :integer
      Person.connection.add_column "people", "height", :float
      Person.connection.add_column "people", "wealth", :decimal, :precision => '30', :scale => '10'
      Person.connection.add_column "people", "birthday", :datetime
      Person.connection.add_column "people", "favorite_day", :date
      Person.connection.add_column "people", "moment_of_truth", :datetime
      Person.connection.add_column "people", "male", :boolean
      Person.reset_column_information

      assert_nothing_raised do
        Person.create :first_name => 'bob', :last_name => 'bobsen',
          :bio => "I was born ....", :age => 18, :height => 1.78,
          :wealth => BigDecimal.new("12345678901234567890.0123456789"),
          :birthday => 18.years.ago, :favorite_day => 10.days.ago,
          :moment_of_truth => "1782-10-10 21:40:18", :male => true
      end

      # Other stuff
end

I think this is just the way it's supposed to be. One reason could be that otherwise they'd have to call reset_column_information after every single operation (add_column, remove_column, etc).

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Ivo Wever January 5th, 2011 @ 10:07 AM
Well, this feature request is for running the method after every Migration; not within the migration after each Model modification. But even then:
```
irb(main):008:0> puts Benchmark.measure {1000000.times {User.reset_column_information;}}
  3.050000   0.010000   3.060000 (  3.079835)
```
I'm not worried about the performance impact of this, the more so since we are dealing on a relatively infrequent operation as running migrations.
rails April 6th, 2011 @ 01:09 AM
- State changed from “new” to “open”
This issue has been automatically marked as stale because it has not been commented on for at least three months.

The resources of the Rails core team are limited, and so we are asking for your help. If you can still reproduce this error on the 3-0-stable branch or on master, please reply with all of the information you have about it and add "[state:open]" to your comment. This will reopen the ticket for review. Likewise, if you feel that this is a very important feature for Rails to include, please reply with your explanation so we can consider it.

Thank you for all your contributions, and we hope you will understand this step to focus our efforts where they are most helpful.
rails April 6th, 2011 @ 01:09 AM
- State changed from “open” to “stale”
You flagged this item as spam.
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- State changed from “stale” to “open”
The resources of the Rails core team are Ray Ban 2140 limited, and so we are asking for your help. If you can still
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