# Foreign key constraints on polymorphic relationships

**URL:** <https://www.ruby-forum.com/t/foreign-key-constraints-on-polymorphic-relationships/145757>\
**Category:** Rails\
**Created:** [August 13, 2008, 6:35pm UTC](https://www.ruby-forum.com/t/foreign-key-constraints-on-polymorphic-relationships/145757 "2008-08-13T18:35:06Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![benjohnson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/3ec8ea/32.png) [@benjohnson](https://www.ruby-forum.com/u/benjohnson)\
**Post date:** [August 13, 2008, 6:35pm UTC](https://www.ruby-forum.com/t/foreign-key-constraints-on-polymorphic-relationships/145757/1 "2008-08-13T18:35:06Z")

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I am setting up foreign key constraints in my database and wasn’t sure  
if it was possible to set them up on polymorphic relationships. Any help  
is greatly appreciated. Thanks.

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<div class="post-metadata">

**Author:** ![benjohnson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/3ec8ea/32.png) [@benjohnson](https://www.ruby-forum.com/u/benjohnson)\
**Post date:** [August 13, 2008, 7:18pm UTC](https://www.ruby-forum.com/t/foreign-key-constraints-on-polymorphic-relationships/145757/2 "2008-08-13T19:18:31Z")

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Hi Ben,

> I am setting up foreign key constraints in my database and wasn’t sure  
> if it was possible to set them up on polymorphic relationships. Any help  
> is greatly appreciated. Thanks.

This isn’t possible by default. A rather complex workaround is to use  
stored procedures that fire on insert and update triggers, but I’d  
advise against it because it’s far from the Rails idiom.

–  
Roderick van Domburg

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