AN@S wrote:
I need your advice regarding the following situation:
In my application I already have a Users table, now I need to add an address book for each user to save his/her contacts, I need also to add the possibility for the user to create groups out of his contacts. As for now I think of the following design:
3 models: User, Address, and Group
User has_many addresses
Address belongs_to User
User has_many groups
Group belongs_to User
Group has_many addresses
Address belongs_to Group
Is this a (healthy) design? Is it better to create a join table?
The great thing about migrations (and unit tests) is you are not stuck with your answers. You can deploy, change your database, and deploy again, without asking your users to re-input all their data.
A group has a name, for your user to tag contacts with. So if an implicit "join table" (for has_and_belongs_to_many) can't have any attributes, you need an explicit one.
However, your current system is not dry. Users have many Groups, and Groups have and belong to many Addresses. If you supply one anonymous Group per User (to hold the Contacts that a User has not yet aligned with any Groups, then you don't need Addresses that belong to Users and Groups at the same time. Multiple ownership is bad like Matrix Management; Contacts should only belong to Groups.
User 1-->* Group *<-->* Contact
User.has_many :groups
Group.belongs_to :user
Group.has_and_belongs_to_many :contacts # and migrate contacts_groups
Contact.has_and_belongs_to_many :groups
User.has_many :contacts, :through => :groups
Contact.has_one :user, :through => :groups
Now report back if the last two lines work. I have never gotten a :through working with a habtm! If they don't work, trivially write accessors to do the same things:
class User
def contacts
groups.map(&:contacts).uniq
end
...
And remember to create one anonymous Group each time you create a User.
