rake db:migrate cause StandardError - uninitialized constant CreateObjects::Object

Question

I have migration 20150930051523_create_objects.rb:

class CreateObjects < ActiveRecord::Migration
def change
  create_table :objects do |t|
    t.text :name
    t.timestamps null: false
  end

  Object.create :name => "A"
  Object.create :name => "B"
  Object.create :name => "C"

  end
end

$ rake:db migrate --trace cause output:
** Invoke db:migrate (first_time)
** Invoke db:environment (first_time)
** Execute db:environment
** Invoke db:load_config (first_time)
** Execute db:load_config
** Execute db:migrate
== 20150930051523 CreateObjects: migrating ====================================
-- create_table(:objects)
   -> 0.0010s
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

uninitialized constant CreateObjects::Object/db/migrate/20150930051523_create_objects.rb:8:in `change'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:605:in `exec_migration'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:589:in `block (2 levels) in migrate'
/usr/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:588:in `block in migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:587:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:765:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:995:in `block in execute_migration_in_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:1041:in `block in ddl_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `block in transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/abstract/transaction.rb:184:in `within_new_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/transactions.rb:220:in `transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:1041:in `ddl_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:994:in `execute_migration_in_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:956:in `block in migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:952:in `each'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:952:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:820:in `up'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:798:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:137:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/railties/databases.rake:44:in `block (2 levels) in '
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `call'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `block in execute'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `each'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `execute'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/usr/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:172:in `invoke_with_call_chain'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:165:in `invoke'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:150:in `invoke_task'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block (2 levels) in top_level'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `each'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block in top_level'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:115:in `run_with_threads'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:100:in `top_level'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:78:in `block in run'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:176:in `standard_exception_handling'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:75:in `run'
/var/lib/gems/2.1.0/gems/rake-10.4.2/bin/rake:33:in `'
/usr/local/bin/rake:23:in `load'
/usr/local/bin/rake:23:in `'
NameError: uninitialized constant CreateObjects::Object/db/migrate/20150930051523_create_barbers.rb:8:in `change'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:605:in `exec_migration'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:589:in `block (2 levels) in migrate'
/usr/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:588:in `block in migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:587:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:765:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:995:in `block in execute_migration_in_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:1041:in `block in ddl_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `block in transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/abstract/transaction.rb:184:in `within_new_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/transactions.rb:220:in `transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:1041:in `ddl_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:994:in `execute_migration_in_transaction'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:956:in `block in migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:952:in `each'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:952:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:820:in `up'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/migration.rb:798:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:137:in `migrate'
/var/lib/gems/2.1.0/gems/activerecord-4.2.4/lib/active_record/railties/databases.rake:44:in `block (2 levels) in '
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `call'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `block in execute'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `each'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `execute'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/usr/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:172:in `invoke_with_call_chain'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:165:in `invoke'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:150:in `invoke_task'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block (2 levels) in top_level'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `each'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block in top_level'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:115:in `run_with_threads'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:100:in `top_level'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:78:in `block in run'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:176:in `standard_exception_handling'
/var/lib/gems/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:75:in `run'
/var/lib/gems/2.1.0/gems/rake-10.4.2/bin/rake:33:in `'
/usr/local/bin/rake:23:in `load'
/usr/local/bin/rake:23:in `'
Tasks: TOP => db:migrate

Error emerging at Object.create... stage, what is wrong?

Answer 1

The problem was solved by set up pg gem, which pull bundle of another gems and packs (particularly postgresql-server-dev-all). After installing it, the command rake db:migrate works fine and completely.

Answer 2

Update: In a comment it was pointed out that the actual code was not containing "Object", this answer is thus based on the wrong example.

Object is a bad name to use for an (unscoped) Model class, as it is already defined by Ruby.

The Object you are calling create on is probably not the Object class you defined in your model sources.

I assume you run rails. Remove the Object.create lines from your migration. Run it, it should work fine. Then, call rails console, where you end up in a live session. Here you can play around with your code, e.g. call Object.create, Object.where{id: 1} etc. I assume that you will get the same errors.

So, as a solution, rename your Object into something else, like Class and look if it works.

Okay, that was a joke, of course Class is also a really bad name for a model class :) . Try to find something more meaningful.