Generalisation in RoR

Rails
1

Hello G.s,

does anybody know wheter RoR is able to implement a generalisation of
a database? I didn’t find any solution for that on the internet.

Example

Person : Customer

or

Person : Employee

in the database such a generalisation is characterized by having the
same PK in Customer and Person or Employee and Person!

2

On 22 May 2011 09:37, Wolfgang [email protected] wrote:

or

Person : Employee

in the database such a generalisation is characterized by having the
same PK in Customer and Person or Employee and Person!

Would Single Table Inheritance (STI) do what you want?

Colin

3

STI is a good approach, but my “subtables” have additional attributes
and afaik this isn’t supportet by STI, is it?

For example:

user << Base
id
firstname
lastname
address
end

employee << user

salary
end

4

Wolfgang wrote in post #1000187:

STI is a good approach, but my “subtables” have additional attributes
and afaik this isn’t supportet by STI, is it?

For example:

user << Base
id
firstname
lastname
address
end

employee << user

salary
end

In the past I used a framework that supported other techniques besides
Single-Table Inheritance. There were actually two other options that
were called Horizontal and Vertical Inheritance. Of those options
Vertical Inheritance was the closest to what we think of as object
inheritance (as you described above), but was also the least efficient.

The issue is that both Horizontal and Vertical inheritance require
multiple queries to get to all the data you need, which causes
performance problems. Even with a framework that supported the other
techniques, using STI was strongly recommended. The performance costs of
either Horizontal or Vertical was simply too high. Inheritance doesn’t
map well to RDBMS. The cost of the null fields in a single table that
contains all attributes for the entire inheritance hierarchy is
negligible compared to the other techniques.

5

On 22 May 2011 11:35, Wolfgang [email protected] wrote:

STI is a good approach, but my “subtables” have additional attributes
and afaik this isn’t supportet by STI, is it?

Yes, you just put the whole set of all attributes in the table. It
wastes a small amount of space in the db but generally that is not an
issue.

Colin

6

Honestly, I’ve always preferred single-table inheritance. I am new to
Rails, but in Java, this is what I’ve always done and it just works
really nicely and it’s more performant than forcing multiple joins
whenever you want to query users - which is probably going to be
often.

I am finding other problems that are Rails-specific with subclasses…
like when submitting forms with simple_for, the parameters hash isn’t
the base class by default, so I am having trouble forcing it to be the
base-class… but structurally, single-table inheritance is a sound
practice. Been doing it for over a decade.

7

Thank you very much for your answers, I’ve decided to use STI