Join 2 tables with custom metadata in Rails

I have a User开发者_Python百科 model, and a Goal model. The Goal model has a name, and a type column, which has the following three records right now.

name           | type
------------------------
Read Novels    | Reading
Read Newspaper | Reading
Write Reviews  | Writing

Now I want to provide each user, an interface to fill in the number of hours they spend on this activity every month (hours_per_month), and the number of different days they do it (days_per_month).

Ideally, I'd want to work with the data like

current_user = User.find(params[:id])

current_user.goals.each do |goal|
  puts goal.name
  puts goal.type
  puts goal.hours_per_month
  puts goal.days_per_month
end

How should I create this new table/model, that joins the Goals to User, and have access to the static Goal attributes, and the user filled values, like the code sample above?

You could create an Activity model and give it a table definition like:

activities:

• user_id
• goal_id
• hours_per_month
• days_per_month

Then add to:

User
  has_many :activities
  has_many :goals, :through => :activity

Goal
  has_many :activities
  has_many :users, :through => :activity

Activity
  belongs_to :user
  belongs_to :goal

You can use a generator to do most of the work iirc.

Table goals_users

column: user_id
column: goal_id
column: hours_worked

Models:

User:

has_and_belongs_to_many :goals

Goals:

has_and_belongs_to_many :users

def hours_per_month
  #calculate
end

def hours_per_day
  #calculate
end

Obviously set up the additional columns outside the join however you like.

Additional

In any model using AR joins you'll need to access the intermediary record directly.