Annotate should reset the cached information about columns

[akihiro17]

Annotate should reset the cached information about columns because Annotate may output old information if we load ActiveRecord::Base class in migration files.

For example, if we have a following migration file and execute rake db:migrate, Annote does not output the default value and a not null constraint of the some_value column.

class CreatePosts < ActiveRecord::Migration
  def change
    create_table :posts do |t|
      t.integer :some_value
    end

    # add a not null constraint to the some_value column

    # should update some_value with not null values
    # because records might exist which have null value in the some_value column

    Post.update_all(some_value: 1)

    change_column_null(:posts, :some_value, false)
    change_column_default(:posts, :some_value, 1)
  end
end

This commit fixes the above issue.

before this commit

# == Schema Information
#
# Table name: posts
#
#  id         :integer          not null, primary key
#  some_value :integer
#

class Post < ActiveRecord::Base
end

after this commit

# == Schema Information
#
# Table name: posts
#
#  id         :integer          not null, primary key
#  some_value :integer          default(1), not null
#

class Post < ActiveRecord::Base
end

[b264]

If you reference an ActiveRecord::Base class in migration files, you are introducing a time-travel problem in your migration. The model code can change, and if your migration is run in the future, say, when a new developer joins or when someone gets a new computer, then it may not work as designed with whatever the new code is. See https://github.com/testdouble/good-migrations I have run into very nasty problems stemming from this in legacy migrations, and I recommend using an SQL statement for the update, YMMV

[ctran]

That's sound advice. @akihiro17, If you re-run migrate, does it fix the annotations (without the suggested fix)?

[akihiro17]

@b264

Thank you for your advice. I've figured out it's not a good idea to access ActiveRecord model objects defined in app/models in migrations.

@ctran

1. redefine the class inside the migration(without this PR)

   does not work as expected because the SchemaCache caches column information for the posts table.

class CreatePosts < ActiveRecord::Migration
  class PostInMigration < ActiveRecord::Base
    self.table_name = :posts
  end

  def change
----
    # should update some_value with not null values
    # because records might exist which have null value in the some_value column
    PostInMigration.update_all(some_value: 1)
---
  end
end

1. use an SQL statement(without this PR)

   works as expected because ActiveRecord does not cache the column information.

class CreatePosts < ActiveRecord::Migration
  def change
---
    # should update some_value with not null values
    # because records might exist which have null value in the some_value column
    execute('update posts set some_value = 1')
---   
  end
end

Thank you.