Multiple relationships between models

rubyonrails-talk
1

Hi, I'm fairly new to RoR and I'm trying to figure out the best way to deal with Users in my application. I've got (for the purpose of this thread) 3 models, User, Subject, and SubjectUserAssignment.

The user model is joined to the Subject model with the following, creating a many to many relationship between User and Subject:

has_many :subjects, :through => :subject_user_assignments has_many :subject_user_assignments

Likewise, the Subject model:

has_many :users, :through => :subject_user_assignments has_many :subject_user_assignments belongs_to :user, :foreign_key => "user_id_created" belongs_to :user, :foreign_key => "user_id_updated"

This works fine, I can return all users for a given subject, and all subjects for a given user. The problem is that the Subject model has user_id_created and user_id_updated fields, which contain the user_id of the user(s) who created and updated the subject. So a user can either be related to a subject because they're assigned to it, or because they created/updated it, or both. How do I go about specifying this in my User model? User.subjects should return all subjects assigned to a user, but I need something else like User.created_subjects to show all subjects created by a user. Am I using :foreign_key correctly in the Subject model?

2

Al Rowan wrote in post #960389:

Hi, I'm fairly new to RoR and I'm trying to figure out the best way to deal with Users in my application. I've got (for the purpose of this thread) 3 models, User, Subject, and SubjectUserAssignment.

The user model is joined to the Subject model with the following, creating a many to many relationship between User and Subject:

has_many :subjects, :through => :subject_user_assignments has_many :subject_user_assignments

I would urge you to find a more descriptive name than SubjectUserAssignment. Perhaps Assignment or even Interest might be better.

Likewise, the Subject model:

has_many :users, :through => :subject_user_assignments has_many :subject_user_assignments belongs_to :user, :foreign_key => "user_id_created" belongs_to :user, :foreign_key => "user_id_updated"

This works fine, I can return all users for a given subject, and all subjects for a given user. The problem is that the Subject model has user_id_created and user_id_updated fields, which contain the user_id of the user(s) who created and updated the subject. So a user can either be related to a subject because they're assigned to it, or because they created/updated it, or both. How do I go about specifying this in my User model? User.subjects should return all subjects assigned to a user, but I need something else like User.created_subjects to show all subjects created by a user. Am I using :foreign_key correctly in the Subject model?

You're using :foreign_key correctly, but you're not using belongs_to correctly. Remember that the first argument to belongs_to is the name of the *association*, not necessarily the class or table. So right now, you're creating two different associations called user (presumably one is overwriting the other). What you want is something like belongs_to :creator, :foreign_key => 'user_id_created', :class_name => 'User' belongs_to :updater, :foreign_key => 'user_id_updated', :class_name => 'User'

Please refer to the belongs_to rdoc for more info on how this all works.

Best,

3

Al Rowan wrote in post #960389:

Hi, I'm fairly new to RoR and I'm trying to figure out the best way to deal with Users in my application. I've got (for the purpose of this thread) 3 models, User, Subject, and SubjectUserAssignment.

The user model is joined to the Subject model with the following, creating a many to many relationship between User and Subject:

has_many :subjects, :through => :subject_user_assignments has_many :subject_user_assignments

Likewise, the Subject model:

has_many :users, :through => :subject_user_assignments has_many :subject_user_assignments belongs_to :user, :foreign_key => "user_id_created" belongs_to :user, :foreign_key => "user_id_updated"

This works fine, I can return all users for a given subject, and all subjects for a given user. The problem is that the Subject model has user_id_created and user_id_updated fields, which contain the user_id of the user(s) who created and updated the subject. So a user can either be related to a subject because they're assigned to it, or because they created/updated it, or both. How do I go about specifying this in my User model? User.subjects should return all subjects assigned to a user, but I need something else like User.created_subjects to show all subjects created by a user. Am I using :foreign_key correctly in the Subject model?

First, unless you fear naming conflicts I think and Assignment model would stand on it's own so I'll present my suggestion based on that.

User

4

Robert Walker wrote in post #960397:

has_many :last_updated_subjects, :class => "Subject", :foreign_key => :last_updated_by_id

Correction: Should have been :class_name not :class

has_many :last_updated_subjects, :class_name => "Subject", :foreign_key => :last_updated_by_id