rails migration in production fails with "Object is not missing Constant User"

Question

I've encountered a strange problem migrating a database in production mode. The initial rake db:migrate fails with error "Object is not missing Constant User", where User is one of my Models, that is accessed in this migration like this:

add_column :users, :feedbacks_count, :integer, :default => 0
    User.reset_column_information
    User.all.each do |u|
      u.update_attribute :feedbacks_count, u.feedbacks.length
    end
end

The logs say the following:

Object is not missing constant User!

/var/lib/gems/1.8/gems/activesupport-2.3.4/lib/active_support/dependencies.rb:417:in `load_missing_constant'

/var/lib/gems/1.8/gems/activesupport-2.3.4/lib/active_support/dependencies.rb:80:in `const_missing_not_from_s3_library'

/var/lib/gems/1.8/gems/aws-s3-0.6.2/lib/aws/s3/extensions.rb:206:in `const_missing'

/var/lib/gems/1.8/gems/activesupport-2.3.4/lib/active_support/dependencies.rb:92:in `const_missing'

/var/lib/gems/1.8/gems/activesupport-2.3.4/lib/active_support/dependencies.rb:98:in `send'

/var/lib/gems/1.8/gems/activesupport-2.3.4/lib/active_support/dependencies.rb:98:in `const_missing'

./db/migrate//20100823185519_add_columns_for_counter_caches.rb:5:in `up_without_benchmarks'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:282:in `send'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:282:in `migrate'

/usr/lib/ruby/1.8/benchmark.rb:293:in `measure'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:282:in `migrate'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:365:in `send'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:365:in `migrate'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:486:in `migrate'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:562:in `call'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:562:in `ddl_transaction'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:485:in `migrate'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:472:in `each'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:472:in `migrate'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:400:in `up'

/var/lib/gems/1.8/gems/activerecord-2.3.4/lib/active_record/migration.rb:383:in `migrate'

/var/lib/gems/1.8/gems/rails-2.3.4/lib/tasks/databases.rake:116

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain'

/usr/lib/ruby/1.8/monitor.rb:242:in `synchronize'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `each'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2001:in `run'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'

/var/lib/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run'

/var/lib/gems/1.8/gems/rake-0.8.7/bin/rake:31 /usr/bin/rake:19:in `load'

/usr/bin/rake:19

I read about a lot of articles, referring to "Object is not missing Constant X" where the problem mainly is referencing models by lazy_loading or accessing plugins. Requiring the 'user.rb' before the add_column or adding a User.new before accessing the users table does not resolve the problem.

Accessing the User model in a migration before the failing one does not cause any trouble either.

Most strange thing about the issue is, that i migrated the same code one day ago to another server, with the same settings and in production as well, where the migration ran without any trouble.

any help would be apreciated!

ernd enson ernd enson · Accepted Answer · 2011-01-11T17:32:42

Of course, I should not require the User model, but add the User class to the Migration by

class User < ActiveRecord::Base; end

thats all there is to do.

What still remains to be checked is, why User model is not known to that Migration....

rails migration in production fails with "Object is not missing Constant User"

2 Answers