Has_to and belongs_to realtionships are not showing up in database

Rails
1

Hello,

I am having what I might think is a basic problem…I can’t get the
relationships of has_many and belongs_to mapped out correctly in the
database. I would expect, according to my MODEL and MIGRATION, that
there
would be a desktop_id in the states and environments DATABASE table ?

How can I get the desktop_id, state_id and environment_id columns mapped
out in the tables ?

I ran rake db:migrate before going to the rails console and checking the
tables…

MODEL:

user@user-DevMachine:~/dev/myapp/app/models$ cat engine.rb
class Engine < ActiveRecord::Base

attr_accessible :title, :body

belongs_to :environment
belongs_to :state
end
user@user-DevMachine:~/dev/myapp/app/models$ cat environment.rb
class Environment < ActiveRecord::Base
attr_accessible :description
has_many :engines
end
user@user-DevMachine:~/dev/myapp/app/models$ cat state.rb
class State < ActiveRecord::Base
attr_accessible :description
has_many :engines
end

MIGRATION:

user@user-DevMachine:~/dev/myapp/db/migrate$ cat
20121225230016_create_engines.rb
class CreateEngines < ActiveRecord::Migration
def change
create_table :engines do |t|

  t.timestamps
end

end
end
user@user-DevMachine:~/dev/myapp/db/migrate$ cat
20121225230034_create_states.rb
class CreateStates < ActiveRecord::Migration
def change
create_table :states do |t|
t.string :description

  t.timestamps
end

end
end
user@user-DevMachine:~/dev/myapp/db/migrate$ cat
20121225230118_create_environments.rb
class CreateEnvironments < ActiveRecord::Migration
def change
create_table :environments do |t|
t.string :description
t.timestamps
end
end
end
user@user-DevMachine:~/dev/myapp/db/migrate$

DATABASE:

user@user-DevMachine:~/dev/myapp/db/migrate$ rails console
Loading development environment (Rails 3.2.9)
1.9.3-p327 :001 > ActiveRecord::Base.connection.execute(“SELECT * FROM
engines”)
(1.1ms) SELECT * FROM engines
=> [{“id”=>1, “created_at”=>“2012-12-26 01:26:38.789476”,
“updated_at”=>“2012-12-26 01:26:38.789476”, 0=>1, 1=>“2012-12-26
01:26:38.789476”, 2=>“2012-12-26 01:26:38.789476”}]
1.9.3-p327 :002 > ActiveRecord::Base.connection.execute(“SELECT * FROM
environments”)
(0.3ms) SELECT * FROM environments
=> [{“id”=>1, “description”=>“warm”, “created_at”=>“2012-12-26
01:27:40.968920”, “updated_at”=>“2012-12-26 01:27:40.968920”, 0=>1,
1=>“warm”, 2=>“2012-12-26 01:27:40.968920”, 3=>“2012-12-26
01:27:40.968920”}, {“id”=>2, “description”=>“cold”,
“created_at”=>“2012-12-26 01:27:41.055711”, “updated_at”=>“2012-12-26
01:27:41.055711”, 0=>2, 1=>“cold”, 2=>“2012-12-26 01:27:41.055711”,
3=>“2012-12-26 01:27:41.055711”}, {“id”=>3, “description”=>“hot”,
“created_at”=>“2012-12-26 01:27:41.129397”, “updated_at”=>“2012-12-26
01:27:41.129397”, 0=>3, 1=>“hot”, 2=>“2012-12-26 01:27:41.129397”,
3=>“2012-12-26 01:27:41.129397”}, {“id”=>4, “description”=>“freezing”,
“created_at”=>“2012-12-26 01:27:41.284936”, “updated_at”=>“2012-12-26
01:27:41.284936”, 0=>4, 1=>“freezing”, 2=>“2012-12-26 01:27:41.284936”,
3=>“2012-12-26 01:27:41.284936”}]
1.9.3-p327 :003 > ActiveRecord::Base.connection.execute(“SELECT * FROM
states”)
(0.4ms) SELECT * FROM states
=> [{“id”=>1, “description”=>“running”, “created_at”=>“2012-12-26
01:27:40.452140”, “updated_at”=>“2012-12-26 01:27:40.452140”, 0=>1,
1=>“running”, 2=>“2012-12-26 01:27:40.452140”, 3=>“2012-12-26
01:27:40.452140”}, {“id”=>2, “description”=>“stopping”,
“created_at”=>“2012-12-26 01:27:40.536188”, “updated_at”=>“2012-12-26
01:27:40.536188”, 0=>2, 1=>“stopping”, 2=>“2012-12-26 01:27:40.536188”,
3=>“2012-12-26 01:27:40.536188”}, {“id”=>3, “description”=>“restarting”,
“created_at”=>“2012-12-26 01:27:40.613507”, “updated_at”=>“2012-12-26
01:27:40.613507”, 0=>3, 1=>“restarting”, 2=>“2012-12-26
01:27:40.613507”,
3=>“2012-12-26 01:27:40.613507”}, {“id”=>4, “description”=>“creating”,
“created_at”=>“2012-12-26 01:27:40.688855”, “updated_at”=>“2012-12-26
01:27:40.688855”, 0=>4, 1=>“creating”, 2=>“2012-12-26 01:27:40.688855”,
3=>“2012-12-26 01:27:40.688855”}, {“id”=>5, “description”=>“destroying”,
“created_at”=>“2012-12-26 01:27:40.768293”, “updated_at”=>“2012-12-26
01:27:40.768293”, 0=>5, 1=>“destroying”, 2=>“2012-12-26
01:27:40.768293”,
3=>“2012-12-26 01:27:40.768293”}]
1.9.3-p327 :004 >

Thanks

Julien E.

2

On Dec 26, 2:25am, Julien E. [email protected] wrote:

Hello,

I am having what I might think is a basic problem…I can’t get the
relationships of has_many and belongs_to mapped out correctly in the
database. I would expect, according to my MODEL and MIGRATION, that there
would be a desktop_id in the states and environments DATABASE table ?

How can I get the desktop_id, state_id and environment_id columns mapped
out in the tables ?

There need to be statements in your migrations to add those columns -
rails won’t look at the models and work it out from the associations
in there.

You may be confusing things with datamapper (that does do this I
think) or with the fact that if you do rails g model foo
belongs_to:bar then rails will add the belongs_to to the model and the
migration.

Fred.

3

Hello Frederick,

As you suggested, i attempted to include this in my scaffold, but when I
rake db:migrate, I get the error:

user@user-user:~/dev/myapp$ rails generate scaffold engine
belongs_to:environment belongs_to:state
invoke active_record
create db/migrate/20121226181404_create_engines.rb
create app/models/engine.rb
invoke test_unit
create test/unit/engine_test.rb
create test/fixtures/engines.yml
invoke resource_route
route resources :engines
invoke scaffold_controller
create app/controllers/engines_controller.rb
invoke erb
create app/views/engines
create app/views/engines/index.html.erb
create app/views/engines/edit.html.erb
create app/views/engines/show.html.erb
create app/views/engines/new.html.erb
create app/views/engines/_form.html.erb
invoke test_unit
create test/functional/engines_controller_test.rb
invoke helper
create app/helpers/engines_helper.rb
invoke test_unit
create test/unit/helpers/engines_helper_test.rb
invoke assets
invoke coffee
create app/assets/javascripts/engines.js.coffee
invoke scss
create app/assets/stylesheets/engines.css.scss
invoke scss
create app/assets/stylesheets/scaffolds.css.scss
user@user-user:~/dev/myapp$ rails generate scaffold environment
description:string has_many:engines
invoke active_record
create db/migrate/20121226181441_create_environments.rb
create app/models/environment.rb
invoke test_unit
create test/unit/environment_test.rb
create test/fixtures/environments.yml
invoke resource_route
route resources :environments
invoke scaffold_controller
create app/controllers/environments_controller.rb
invoke erb
create app/views/environments
create app/views/environments/index.html.erb
create app/views/environments/edit.html.erb
create app/views/environments/show.html.erb
create app/views/environments/new.html.erb
create app/views/environments/_form.html.erb
invoke test_unit
create test/functional/environments_controller_test.rb
invoke helper
create app/helpers/environments_helper.rb
invoke test_unit
create test/unit/helpers/environments_helper_test.rb
invoke assets
invoke coffee
create app/assets/javascripts/environments.js.coffee
invoke scss
create app/assets/stylesheets/environments.css.scss
invoke scss
identical app/assets/stylesheets/scaffolds.css.scss
user@user-user:~/dev/myapp$ rails generate scaffold state
description:string has_many:engines
invoke active_record
create db/migrate/20121226181504_create_states.rb
create app/models/state.rb
invoke test_unit
create test/unit/state_test.rb
create test/fixtures/states.yml
invoke resource_route
route resources :states
invoke scaffold_controller
create app/controllers/states_controller.rb
invoke erb
create app/views/states
create app/views/states/index.html.erb
create app/views/states/edit.html.erb
create app/views/states/show.html.erb
create app/views/states/new.html.erb
create app/views/states/_form.html.erb
invoke test_unit
create test/functional/states_controller_test.rb
invoke helper
create app/helpers/states_helper.rb
invoke test_unit
create test/unit/helpers/states_helper_test.rb
invoke assets
invoke coffee
create app/assets/javascripts/states.js.coffee
invoke scss
create app/assets/stylesheets/states.css.scss
invoke scss
identical app/assets/stylesheets/scaffolds.css.scss
user@user-user:~/dev/myapp$ rake db:create
user@user-user:~/dev/myapp$ rake db:migrate
== CreateEngines: migrating

– create_table(:engines)
rake aborted!
An error has occurred, this and all later migrations canceled:

undefined method environment' for #<ActiveRecord::ConnectionAdapters::TableDefinition:0x00000001ca2ff0> /home/user/temp/project/db/migrate/20121226181404_create_engines.rb:4:inblock in change’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/connection_adapters/abstract/schema_statements.rb:160:in
create_table' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:466:inblock in method_missing’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:438:in
block in say_with_time' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:438:insay_with_time’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:458:in
method_missing' /home/user/temp/project/db/migrate/20121226181404_create_engines.rb:3:inchange’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:407:in
block (2 levels) in migrate' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:407:inblock in migrate’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/connection_adapters/abstract/connection_pool.rb:129:in
with_connection' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:389:inmigrate’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:528:in
migrate' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:720:inblock (2 levels) in migrate’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:775:in
call' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:775:inblock in ddl_transaction’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in
transaction' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/transactions.rb:208:intransaction’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:775:in
ddl_transaction' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:719:inblock in migrate’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:700:in
each' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:700:inmigrate’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:570:in
up' /home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/migration.rb:551:inmigrate’
/home/user/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.9/lib/active_record/railties/databases.rake:179:in
block (2 levels) in <top (required)>' /home/user/.rvm/gems/ruby-1.9.3-p327/bin/ruby_noexec_wrapper:14:ineval’
/home/user/.rvm/gems/ruby-1.9.3-p327/bin/ruby_noexec_wrapper:14:in
`’
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

4

On Dec 26, 6:19pm, Julien E. [email protected] wrote:

Hello Frederick,

As you suggested, i attempted to include this in my scaffold, but when I
rake db:migrate, I get the error:

You probably don’t want to include the has_many - since that requires
a column on the other table. Other than that, take a look at the
generated migration.

To be honest i don’t bother with the belongs_to shortcuts for
migrations - I just add the columns as ‘normal’ columns and then edit
the model

Fred

5

upon further investigation and a lot of googling, i have found that in
order to get environment_id and state_id columns into the engines table,
I
have to add

t.belongs_to :environment
t.belongs_to :state

into the migrations files.

Thanks for the assistance Frederic. :slight_smile: