On 4/5/07, jack.tang <himars / gmail.com> wrote:
> Hi
>
> In the classic hasmanythrough example:
>
> class Group < ActiveRecord::Base
>         has_many :memberships
>         has_many :users, :through => :memberships
> end
>
> class User < ActiveRecord::Base
>         has_many :memberships
>         has_many :groups, :through => :memberships
> end

Where's your Membership model?  I think you need something like:

   class Membership < ActiveRecord::Base
           belongs_to :group
           belongs_to :user
    end

> group1 = Group.new(.....)
> group1.users = [User.find_by_id(2)]
> group1.save!


>
> it throws the exception: "users=" is one undefined method. So how can
> i save the relationship in hasmanythrough?

This has nothing to do with the :through option.  The :has_many
relationship doesn't add a setter.  Instead you need to use methods on
the attribute, which is not a normal ruby array but an ActiveRecord
object which looks like an Array but is doing the right SQL magic
under the covers.

Some useful methods include:
    group1.users<< user # add a user
    group1.users.push(user1, user2, ...) add one or more users
    group1.users.replace(user1, ...) replace users with one or more users
    group1.users.delete(user1, ...) delete one or more users.


If you want to create a :has_many:through: relationship using just the
two ends, both far ends of the association need to exist on the
database:

group1 = Group.create(...)  # group needs to have been previously saved
                                             # ... represents
attributes to be set in the group
group1.users << User.find_by_id(2)

Or to create a new user and add it to the group:

group1 = Group.create(...)
article.users.create!(...)

If you want to have attributes in the membership if you don't why are
you using has_many:through:?   Then you need to create the
intermediate table yourself.  So lets' say the membership is used to
hold things like when it expires:

membership = Membership.new
membership.expiration = Time.now.next_year.to_date
membership.group = Group.find_by_id(3) # or how ever you get the group
membership.user = User.find_by_username("Dirk Gently")
membership.save

You'll probably get more help with ActiveRecord questions on more
rails specific resources:
http://www.rubyonrails.org/community

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/