# How to properly set association to a self junction table?
**URL:** https://discourse.rom-rb.org/t/how-to-properly-set-association-to-a-self-junction-table/696
**Category:** Uncategorized
**Created:** [May 22, 2025, 2:10pm UTC](https://discourse.rom-rb.org/t/how-to-properly-set-association-to-a-self-junction-table/696 "2025-05-22T14:10:16Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@Franck](https://discourse.rom-rb.org/u/Franck)
#### Post date: [May 22, 2025, 2:10pm UTC](https://discourse.rom-rb.org/t/how-to-properly-set-association-to-a-self-junction-table/696/1 "2025-05-22T14:10:17Z")
Hi there,
I’m trying to figure out my association setting. Here is a MWE :
A users table, and a mentoring table. Each user can mentor any number of other users (mentees). And each mentee could be mentored by any number of other users (mentors).
- Migration :
```auto
ROM::SQL.migration do
change do
create_table :users do
primary_key :id
column :name, String, null: false
end
create_table :mentoring do
primary_key :id
foreign_key :mentor_id, :users, null: false # eventually here unique: true if only one mentor allowed
foreign_key :mentee_id, :users, null: false
end
end
end
```
- seeds :
```auto
users : [
{:id=>1, :name=>"Alice"},
{:id=>2, :name=>"Bob"},
{:id=>3, :name=>"Chuck"},
{:id=>4, :name=>"Doug"},
{:id=>5, :name=>"Erny"}
]
mentoring : [
{:id=>1, :mentor_id=>1, :mentee_id=>2},
{:id=>2, :mentor_id=>1, :mentee_id=>3},
{:id=>3, :mentor_id=>2, :mentee_id=>3},
{:id=>4, :mentor_id=>3, :mentee_id=>4},
{:id=>5, :mentor_id=>2, :mentee_id=>5}
]
```
- relations :
```auto
schema :users, infer: true do
associations do
has_many :mentees, through: :mentoring, foreign_key: :mentor_id, relation: :users, as: :mentees
has_many :mentors, through: :mentoring, foreign_key: :mentee_id, relation: :users, as: :mentors
end
end
schema :mentoring, infer: true do
associations do
belongs_to :mentee, foreign_key: :mentee_id, relation: :users
belongs_to :mentor, foreign_key: :mentor_id, relation: :users # this seems to fail !
end
end
```
Then :
- `users.combine(:mentees).to_a` leads to the expected result :
```auto
[
{:id=>1, :name=>"Alice", :mentees=> [{:id=>2, :name=>"Bob", :mentor_id=>1}, {:id=>3, :name=>"Chuck", :mentor_id=>1}]},
{:id=>2, :name=>"Bob", :mentees=> [{:id=>3, :name=>"Chuck", :mentor_id=>2}, {:id=>5, :name=>"Erny", :mentor_id=>2}]},
{:id=>3, :name=>"Chuck", :mentees=>[{:id=>4, :name=>"Doug", :mentor_id=>3}]},
{:id=>4, :name=>"Doug", :mentees=>[]},
{:id=>5, :name=>"Erny", :mentees=>[]}
]
```
- `users.combine(:mentors).to_a` leads to a curious result. Mentor numbers are correct but their identity is “replaced by” meetee identity. I think this is because only one `belongs_ to` statement (the first) is taken into account. Commenting out this first `belongs_to` statement leads to things changed : I can obtain mentors but not mentees.
```auto
[
{:id=>1, :name=>"Alice", :mentors=>[]},
{:id=>2, :name=>"Bob", :mentors=>[{:id=>2, :name=>"Bob", :mentee_id=>2}]},
{:id=>3, :name=>"Chuck", :mentors=> [{:id=>3, :name=>"Chuck", :mentee_id=>3}, {:id=>3, :name=>"Chuck", :mentee_id=>3}]},
{:id=>4, :name=>"Doug", :mentors=>[{:id=>4, :name=>"Doug", :mentee_id=>4}]},
{:id=>5, :name=>"Erny", :mentors=>[{:id=>5, :name=>"Erny", :mentee_id=>5}]}
]
```
Anyone to help me fixing this ? Any advice/guide on relation options usage (:source, :target, :relation, etc.) ?
Thanks !
---
### Author:  [@Franck](https://discourse.rom-rb.org/u/Franck)
#### Post date: [May 23, 2025, 6:59am UTC](https://discourse.rom-rb.org/t/how-to-properly-set-association-to-a-self-junction-table/696/2 "2025-05-23T06:59:33Z")
The night was good for me. The solution is to tie 2 relations to the mentoring table, correctly aliased. See :
```auto
# relations/user_mentees.rb
schema :mentoring, as: :user_mentees, infer: true do
associations do
belongs_to :mentee, foreign_key: :mentee_id, relation: :users
end
end
```
```auto
# relations/user_mentors.rb
schema :mentoring, as: :user_mentors, infer: true do
associations do
belongs_to :mentor, foreign_key: :mentor_id, relation: :users
end
end
```
then,
```auto
# relations/users.rb
schema :users, infer: true do
associations do
has_many :mentees,
through: :user_mentees,
foreign_key: :mentor_id,
relation: :users,
as: :mentees
has_many :mentors,
through: :user_mentors,
foreign_key: :mentee_id,
relation: :users,
as: :mentors
end
end
```
I now enjoy seeing `users.combine(:mentees).to_a` together with `users.where(name: 'Bob').combine(:mentees).to_a` in one hand, and `users.combine(:mentors).to_a` together with `users.where(name: 'Bob').combine(:mentors).to_a` in another hand, working like a charm.