ruby - Rails associations has_many through instead of HABTM -

i'm new rails , activerecord , i'm trying find correct way model data.

i building application let's swim instructors put class plan shows skills teaching class , activities use teach each skill. plan can contain many skills , each skill can have many activities associated it.

on plan form there widget skill-activity combination. in it, user should able select skill dropdown , selected skill select multiple activities list. widget can repeat number of times on form.

my current model:

class plan   has_many :plan_activities end  class planactivities   belongs_to :plan   belongs_to :skill   has_and_belongs_to_many :activities end  class skill end  class activity end 

is model correct? problem accepts_nested_attribtues_for not work habtm associations. i've read can replace has_many through:, mean adding yet join model picture. seems little ugly. there better way this?

edit:

my skills , activities in list form , should able include same skill and/or activity on multiple plans.

your model close. 1 improvement here remove planactivities model. have associations directly on plan. @ point don't think model justified. have pretty basic pyramid structure here. @ top plan many skills, each skill has many activities, simpler model like:

class plan   has_many :plan_skills   has_many :activities, through: :plan_skills end  class skill   has_many :activities, through: plan_skills   has_many :plan_skills  end  class planskill   belongs_to :plan   belongs_to :skill   has_many :activities end   class activity   belongs_to :plan_skill end 

the join model option not entirely necessary here. plan.activities make needed join table you.