# Self-referential symmetrical relation problem

**URL:** <https://www.ruby-forum.com/t/self-referential-symmetrical-relation-problem/88290>\
**Category:** Rails\
**Created:** [March 9, 2007, 1:41pm UTC](https://www.ruby-forum.com/t/self-referential-symmetrical-relation-problem/88290 "2007-03-09T13:41:55Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Trochalakis\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/f475e1/32.png) [@Trochalakis\_C](https://www.ruby-forum.com/u/Trochalakis_C)\
**Post date:** [March 9, 2007, 1:41pm UTC](https://www.ruby-forum.com/t/self-referential-symmetrical-relation-problem/88290/1 "2007-03-09T13:41:55Z")

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I found the following code here:

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I 'm trying to add an additional “has\_many :teamates” on the player  
model but i cant figure out how to do it…

Any ideas?

Thanks in advance!  
Chris

The Code:

# class Player \< ActiveRecord::Base

# has\_many :team\_memberships

# has\_many :teams, :through =\> :team\_memberships

# end

# 

# class TeamMembership \< ActiveRecord::Base

# belongs\_to :player

# belongs\_to :team

# end

# 

# class Team \< ActiveRecord::Base

# has\_many :team\_memberships

# has\_many :players, :through =\> :team\_memberships

# has\_many :ratings

# end

# 

# class Rating \< ActiveRecord::Base

# belongs\_to :team

# end

---

<div class="post-metadata">

**Author:** ![Trochalakis\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/f475e1/32.png) [@Trochalakis\_C](https://www.ruby-forum.com/u/Trochalakis_C)\
**Post date:** [March 9, 2007, 3:41pm UTC](https://www.ruby-forum.com/t/self-referential-symmetrical-relation-problem/88290/2 "2007-03-09T15:41:28Z")

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class Player \< ActiveRecord::Base  
has\_many :teammates, :class\_name =\> ‘Player’  
end

Then just add the field player\_id to the players table, and it should  
work  
fine.

---

<div class="post-metadata">

**Author:** ![Trochalakis\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/f475e1/32.png) [@Trochalakis\_C](https://www.ruby-forum.com/u/Trochalakis_C)\
**Post date:** [March 9, 2007, 4:23pm UTC](https://www.ruby-forum.com/t/self-referential-symmetrical-relation-problem/88290/3 "2007-03-09T16:23:38Z")

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Ï/Ç Luke I. Ýãñáøå:

> class Player \< ActiveRecord::Base  
> has\_many :teammates, :class\_name =\> ‘Player’  
> end
> 
> Then just add the field player\_id to the players table, and it should work  
> fine.

Nope, that wouldn’t work. What i want is to find the teammates through  
the other tables.

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<div class="post-metadata">

**Author:** ![Trochalakis\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/f475e1/32.png) [@Trochalakis\_C](https://www.ruby-forum.com/u/Trochalakis_C)\
**Post date:** [March 12, 2007, 3:00pm UTC](https://www.ruby-forum.com/t/self-referential-symmetrical-relation-problem/88290/4 "2007-03-12T15:00:43Z")

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On Mar 9, 6:26 pm, “eden li” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> … i _think_ that works…

Thanks a lot eden li! 🙂

---

<div class="post-metadata">

**Author:** ![Trochalakis\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/f475e1/32.png) [@Trochalakis\_C](https://www.ruby-forum.com/u/Trochalakis_C)\
**Post date:** [March 9, 2007, 5:35pm UTC](https://www.ruby-forum.com/t/self-referential-symmetrical-relation-problem/88290/5 "2007-03-09T17:35:00Z")

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You’ll likely need to go to SQL here… Join the tables together and  
return the result based on the memberships of the instance-level  
player.

has\_and\_belongs\_to\_many :teammates,  
:join\_table =\> TeamMembership.table\_name,  
:finder\_sql =\> “SELECT p2.\* FROM #{TeamMembership.table\_name} AS  
t1 INNER JOIN #{Player.table\_name} AS p1 ON t1.player\_id = p1.id INNER  
JOIN #{Player.table\_name} AS p2 ON p2.team\_id = t1.team\_id WHERE p1.id  
= #{id} AND p2.id != #{id}”

… i _think_ that works…

On Mar 9, 7:49 pm, “Trochalakis C.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)