Rails has_and_belongs_to_many collection methods not showing up on object

Question

I have a problem with has_and_belongs_to_many in a Rails 4 app. The setup is as follows:

A User can have several Roles
A Role can have several Permissions

Since many Users can share the same Roles, and many Roles can share the same Permissions, and I don't need special connection models between them, I am using has_and_belongs_to_many for both these relationships.

Here are the models (stripped of validations):

class User < ActiveRecord::Base
  has_and_belongs_to_many :roles
end

class Role < ActiveRecord::Base
  has_and_belongs_to_many :permissions
  has_and_belongs_to_many :users
end

class Permission < ActiveRecord::Base
  has_and_belongs_to_many :roles
end

The join tables are named as per convention:

create_table "permissions_roles" do |t|
  t.integer "role_id"
  t.integer "permission_id"
end

create_table "roles_users" do |t|
  t.integer "role_id"
  t.integer "user_id"
end

Roles <-> Permissions works great, but Users <-> Roles seems to work only one way. I can attach Users to Roles, but not Roles to Users – the collection methods do not exist on the User objects. From the rails console:

> r = Role.first # Fetch a role
> r.users        # Empty list of users -- so far so good
> u = User.first # Fetch a user
> u.roles        # NoMethodError: undefined method `roles' for #<User:0x007fe67562f580>

Any idea what could be going on here?

Update:

When I run User.has_and_belongs_to_many :roles from the console, the association is correctly set up and I can run User.first.roles without issue. It seems the association for some reason isn't set up when the application is bootstrapped.

Surely permissions would be programmatic? I mean, do you need a database to house them? — Richard Peck, Mar 21 '14 at 10:42
@Rich Peck: Well, yes, and we're changing that, but that's besides the point here. The relationship should still work. — arnemart, Mar 21 '14 at 11:16
I suppose you are doing it wrong.The HABTM relation should have one join model with the corresponding two other models on which the relation is set.Correct me if i'm wrong. — Pavan, Mar 21 '14 at 11:26
give this a try: `r.reflect_on_association(users)` `u.reflect_on_association(roles)` - if the output of these is the same, then i don't know :P if it's not, i suggest you take a look at your `user` and `role` tables (not the join tables) — dax, Mar 21 '14 at 11:28
@Pavan: No, that's a `has_many :through`-relation. HABTM does not need a join model. — arnemart, Mar 21 '14 at 11:28
ah, or better: `r.reflect_on_all_associations` and `u.reflect_on_all_associations` — dax, Mar 21 '14 at 11:30
Actually it does need I think so by seeing this guide http://guides.rubyonrails.org/association_basics.html#the-has-and-belongs-to-many-association — Pavan, Mar 21 '14 at 11:30
read that link again, Paven. First sentence: A has_and_belongs_to_many association creates a direct many-to-many connection with another model, **with no intervening model**. — dax, Mar 21 '14 at 11:30
@dax oops! Misjudged by seeing the picture of it.Apologies to the OP. — Pavan, Mar 21 '14 at 11:32
dax: The association shows up when doing `Role.reflect_on_all_associations`, but not when doing `User.reflect_on_all_associations`. This is weird. — arnemart, Mar 21 '14 at 11:33
not sure why this would work, but try changing order of habtm in Role.rb? — dax, Mar 21 '14 at 11:36
maybe check out the [docs](http://guides.rubyonrails.org/association_basics.html#has-and-belongs-to-many-association-reference) — dax, Mar 21 '14 at 11:40
@dax: I tried changing the order, it does not seem to do anything. — arnemart, Mar 21 '14 at 11:56

score 0 · Answer 1 · edited Mar 21 '14 at 13:23

Maybe you should consider using has_many, :through

Here is an example

From rubyonrails.org:

class Assembly < ActiveRecord::Base
  has_many :manifests
  has_many :parts, through: :manifests
end

class Manifest < ActiveRecord::Base
  belongs_to :assembly
  belongs_to :part
end

class Part < ActiveRecord::Base
  has_many :manifests
  has_many :assemblies, through: :manifests
end

More ressources on:

score 0 · Answer 2 · answered Mar 21 '14 at 14:04

0

Solved it, it was extremely project-specific. All our models need to be used across multiple projects, so they live in their own gem. Turns out there was a different User model in another location that superseded the one in the gem.

answered Mar 21 '14 at 14:04

arnemart

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Rails has_and_belongs_to_many collection methods not showing up on object

2 Answers2