"uninitialized constant" error during migration - mysql

Question

I'm a newbie in Ruby on Rails and I want to generate a mysql database using migrations.
I tried this command
ruby bin/rake db:drop db:create db:migrate --trace
but I always get this error:
rake aborted!
StandardError: An error has occurred, all later migrations canceled:
uninitialized constant CreateOrganisation::Referential
C:/Sites/blog/db/migrate/20120823053740_create_organisation.rb:13:in `up'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:598:in `exec_migration'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/2.0.0/benchmark.rb:281:in `measure'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in `block in migrate'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with
_connection'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in `migrate'
C:in `migrate'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in `block in execute_migration_in_transacti
on'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:1039:in `ddl_transaction'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in `execute_migration_in_transaction'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in `block in migrate'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `each'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `migrate'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in `up'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in `migrate'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in `block (2 levels) in <top (req
uired)>'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `call'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `block in execute'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `each'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `execute'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/2.0.0/monitor.rb:211:in `mon_synchronize'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/task.rb:172:in `invoke_with_call_chain'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/task.rb:165:in `invoke'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:150:in `invoke_task'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block (2 levels) in top_level'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `each'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block in top_level'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:115:in `run_with_threads'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:100:in `top_level'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:78:in `block in run'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:176:in `standard_exception_handling'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/rake-10.4.2/lib/rake/application.rb:75:in `run'
bin/rake:4:in `<main>'
Tasks: TOP => db:migrate
I tried the commands:
rake db:rollback
rake db:reset
rake db:schema:dump
rake db:schema:load
but in vain.
The file that causes the error (I guess) is:
class CreateOrganisation < ActiveRecord::Migration
def up
create_table :organisations do |t|
t.string :name
t.timestamps
end
change_table :referentials do |n|
n.belongs_to :organisation
end
change_table :users do |u|
u.belongs_to :organisation
end
Referential.reset_column_information
User.reset_column_information
organisation = Organisation.find_or_create_by_name!("Chouette")
Referential.update_all :organisation_id => organisation.id
User.update_all :organisation_id => organisation.id
end
def down
drop_table :organisations
end
end
I tried putting def change..end instead of def up..end/def down..end but I still get the same error
I can't see what I'm missing here.

Answer 1

You're trying to change the table referential and it doesn't exist:
change_table :referentials do |n|
n.belongs_to :organisation
end
The error refers to an uninitialized constant ":referentials", which refers to that particular table.
Consider using a generator to create your migrations until you understand how they work; you can always tweak the generated migrations or write your own from scratch later.
Example
rails generate migration CreateFoo name:string amount:integer owner:string:index
And that will create
class CreateFoo < ActiveRecord::Migration
def change
create_table :foos do |t|
t.string :name
t.integer :amount
t.string :owner
end
add_index :foos, :owner
end
end
Reference
I suggest you read the Rails Migration Guide, which should help you understand how to use migrations.