activerecord - rails many to many relationship from the beginning (all model creation) -

i've read lot of questions on , migration guides , api , not clear. of answers assume have models , tables 2 entities. i'm starting scratch need full solution. have drugs , drug classes. drugs can in many drug classes , drug classes have many drugs. what's best way set up? i'd use rails generate.

using: ruby 1.9.3p286 (2012-10-12 revision 37165) [x86_64-darwin11.4.0] rails 4.0.0.beta1

where can use generate , generate start , edit files created generate command?

i don't difference between has , belongs many , has many through.

i've run far....

switched branch 'drugclasses' ➜  lm git:(drugclasses) ✗ rails generate model drug name:string   invoke  active_record   create    db/migrate/20130502191118_create_drugs.rb   create    app/models/drug.rb   invoke    rspec   create      spec/models/drug_spec.rb   invoke      factory_girl   create        spec/factories/drugs.rb ➜  lm git:(drugclasses) ✗ rails generate model drug_class name:string   invoke  active_record   create    db/migrate/20130502191208_create_drug_classes.rb   create    app/models/drug_class.rb   invoke    rspec   create      spec/models/drug_class_spec.rb   invoke      factory_girl   create        spec/factories/drug_classes.rb ➜  lm git:(drugclasses) ✗ rails generate model drugs_drug_classes drug:references drug_class:references   invoke  active_record   create    db/migrate/20130502191606_create_drugs_drug_classes.rb   create    app/models/drugs_drug_classes.rb   invoke    rspec   create      spec/models/drugs_drug_classes_spec.rb   invoke      factory_girl   create        spec/factories/drugs_drug_classes.rb ➜  lm git:(drugclasses) ✗  

and here what's been generated.

➜  lm git:(drugclasses) ✗ cat db/migrate/20130502191118_create_drugs.rb  class createdrugs < activerecord::migration   def change     create_table :drugs |t|       t.string :name        t.timestamps     end   end end ➜  lm git:(drugclasses) ✗ cat db/migrate/20130502191208_create_drug_classes.rb  class createdrugclasses < activerecord::migration   def change     create_table :drug_classes |t|       t.string :name        t.timestamps     end   end end ➜  lm git:(drugclasses) ✗ cat db/migrate/20130502191606_create_drugs_drug_classes.rb  class createdrugsdrugclasses < activerecord::migration   def change     create_table :drugs_drug_classes |t|       t.references :drug, index: true       t.references :drug_class, index: true        t.timestamps     end   end end ➜  lm git:(drugclasses) ✗  

i have not run rake db:migrate. if i've done wrong, how roll right spot? delete files created? trash branch see created it.

thanks in advance!

_____update______

ok destroyed previous (rails destroy model drugs_drug_classes) , instead did this:

rails g migration createjointabledrugdrugclass drug drug_class 

and generated this: class createjointabledrugdrugclass < activerecord::migration def change create_join_table :drugs, :drug_classes |t| # t.index [:drug_id, :drug_class_id] # t.index [:drug_class_id, :drug_id] end end end

1. why indices commented out? ran migration , indexes created (i see them in schema). that's confusing!

2. why doesn't migration add associations drug , drugclass models?!