How do I show attributes for has_many associations in Rails 3?

I have a Contact which has_many Campaigns.

And a Campaign has_many Contacts开发者_如何转开发.

However, a Contact may have a start_date and a status for each Campaign.

For Example:

 Contact A   is active and start_date = 4/4/11 for Campaign 1 

 Contact A   is stopped and start_date = 3/2/11 for Campaign 1

Thanks.

has_many :through lets you define attributes on the join table which pertain to the relationship itself.

class Contact
  has_many :campaign_contacts
  has_many :campaigns, :through => :campaign_contacts
end

class CampaignContact
  belongs_to :contact
  belongs_to :campaign
end

class Campaign
  has_many :campaign_contacts
  has_many :contacts, :through => :campaign_contacts
end

Normally you would just add the foreign keys to the join table and be done with it. But you can also add other columns:

t.integer :contact_id
t.integer :campaign_id
t.date    :start_date
t.status  :string # 'active','stopped'

Now you can assign the attributes to the relationship:

campaign1 = Campaign.find(1)
campaign2 = Campaign.find(2)
contactA = Contact.find_by_name("A")
contactA.campaign_contacts.build(:status=>'active',
  :start_date => '2011-04-04',:campaign=>campaign1)
contactA.campaign_contacts.build(:status=>'stopped',
  :start_date => '2011-03-02',:campaign=>campaign1)