Polymorphism in SQL database

[cobra2008]

I find myself faced with a problem that can be summarized as follows:

I have a class "box" which can contain 0-N "Crafts", "Subject" is a common interface to several other classes, with a single point in common is that they may be in the same box. Box may contain multiple instances of the same class, only one instance of several different classes or a mix of both.

This does not pose major problems as I manage it in my program, I'm against a little taken when designing the corresponding tables: How to translate this relationship knowing that I can not create a table with FK object_1 , object_2 ... knowing that I can not know how many there will be objects in each box, create a table join box_id => object_id, as each class will have its own table (they all have separate fields).

[Lemog]

Your design object is in what language? Because my impression is that you poses problems solved by all MNOs.

[cobra2008]

It is in Ruby on Rails web framework. Do you think its the problem of Ruby on Rails design? The least worst that I have found yet is to join a table:

- Box_id, object_id, class_name, containing for example:

1, 1, "Shoes"
1, 2, "Shoes"
1, 1, "Bicycle"
...

The 1st request is beyond what is in box 1, then there would be a request by families of objects:

select * from Shoes where id = 1 or id = 2
select * from Bicycle where id = 1
...

Given that there will not be hundreds of items per box it's still viable, but I must admit that I'm moderately excited about setting up something