# Table linking questions

**URL:** <https://www.ruby-forum.com/t/table-linking-questions/115974>\
**Category:** Rails\
**Created:** [October 1, 2007, 5:49am UTC](https://www.ruby-forum.com/t/table-linking-questions/115974 "2007-10-01T05:49:17Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Jack720](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/278dde/32.png) [@Jack720](https://www.ruby-forum.com/u/Jack720)\
**Post date:** [October 1, 2007, 5:49am UTC](https://www.ruby-forum.com/t/table-linking-questions/115974/1 "2007-10-01T05:49:17Z")

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I’m about to try coding a quick test app as my first rails test.

My first question should be quick. how do I include two ids in the  
same table. for example relating two people together.

people

* * *

id  
name

relationships

* * *

id  
person\_id  
person\_id (what would this be called)  
relationship\_type

My second question is probably more of a general DB design question  
but I wasn’t sure if there was an effecient ruby way of doing this.

Lets say I have 3 tables:

people

* * *

id  
name

products

* * *

id  
name  
cost

notes

* * *

id  
detail

I’d like people and products to both be able to have multiple notes.  
The app I want to build is going to have a lot of these types of  
relationships and I wanted to know the best way to tie them together.  
I have a few ideas but nothing I’m too hot about.

Option 1 (best?)  
a seperate objects table with a unique id that is shared by all tables  
involved.

objects

* * *

id (unique in people and products, only one record in any table  
anywhere)  
type (person, product, note)  
timestamp(s)

people

* * *

id  
object\_id  
name

products

* * *

id  
object\_id  
name  
cost

notes

* * *

id  
object\_id  
object\_id\_link ? (tie to products or person)  
detail

Option 2  
I could add fields in notes for each table I want to link to.

people

* * *

id  
name

products

* * *

id  
name  
cost

notes

* * *

id  
person\_id (only person or product would be populated but not both)  
product\_id  
detail

Option 3  
I could create a seperate table for each relationship

people

* * *

id  
name

products

* * *

id  
name  
cost

notes

* * *

id  
detail

people\_notes\_associations

* * *

id  
person\_id  
note\_id

products\_notes\_associations

* * *

id  
product\_id  
note\_id

The problem with options 2 and 3 is that while they would be OK for 2  
tables if I have 4 or 5 it gets messy and cumbersom. ideas?

---

<div class="post-metadata">

**Author:** ![Jack720](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/278dde/32.png) [@Jack720](https://www.ruby-forum.com/u/Jack720)\
**Post date:** [October 1, 2007, 6:19am UTC](https://www.ruby-forum.com/t/table-linking-questions/115974/2 "2007-10-01T06:19:05Z")

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For your first question, the second person\_id could be called parent\_id,  
stating that that person is the parent of the parent / child  
relationship. For your second question, you should look into polymorphic  
relationships. You can read more about them here:  
[http://wiki.rubyonrails.org/rails/pages/UnderstandingPolymorphicAssociations](http://wiki.rubyonrails.org/rails/pages/UnderstandingPolymorphicAssociations)

I hope this helps.

-Bill

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<div class="post-metadata">

**Author:** ![Jack720](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/278dde/32.png) [@Jack720](https://www.ruby-forum.com/u/Jack720)\
**Post date:** [October 1, 2007, 7:36am UTC](https://www.ruby-forum.com/t/table-linking-questions/115974/3 "2007-10-01T07:36:14Z")

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actually on the first question it couldn’t be parent\_id because the  
relationship would depend on the type. sometimes a parent/child  
sometimes a spouse/child or maybe an adoption. etc. I thought rails  
picked up relationships based on convention so i wanted to tie both  
fields to the same table. I guess I wanted to know the convention for  
that.

I’ll look into polymorphic relationships  
Thank you.