DRY naming, or polymorphic join models

Rails
1

I need to DRY up some of my tables. Here is the situation: I have a
number of objects that habtm name objects. What I need is some kind
of polymorphic join model so each object can relate to the same names
table. An example:

oranges table
orange row
orange row
…

apples table
apple row
apple row
…

names table
valencia
red delicious
gala
navel
blood orange
…

I need to break the names out because some of the oranges or apples
have different names, but the same other data. Am I stuck with a
names table and join model for each fruit, or can I do something
tricky with has_many :through and meta-data?
TIA,
–Dean

2

What about single-table inheritance (STI)? It would allow you do
something
like the following:

fruits table

  • name
  • color
  • type (Orange, Apple, etc.)

class Fruit < ActiveRecord::Base; end
class Apple < Fruit; end
class Orange < Fruit; end

More information here:

http://wiki.rubyonrails.org/rails/pages/SingleTableInheritance
http://www.martinfowler.com/eaaCatalog/singleTableInheritance.html

On 2/12/07, Dean [email protected] wrote:

…
navel

–
Michael G.

3

On Feb 12, 10:45 am, “Michael G.” [email protected] wrote:

class Orange < Fruit; end
I thought about that, but I have way too much information about my
“fruits” plus five different types of “fruit” to mash into one table.
I may have to hack together some cool join model.
–Dean

4

Don’t try to break shared columns out into their own table. It’s a
significant complication for no performance gain.

Just use Single Table Inheritance or Polymorphic Associations,
dpeending on what you’re trying to do. We can’t tell what’s
appropriate, because you only described your twisted data structure,
without telling us what you’re trying to model. :slight_smile:

Ciao,
Sheldon.

5

On Feb 13, 12:16 am, “Sheldon H.” [email protected] wrote:

P.S.: It’s probably a mistake to produce one class per type of fruit.
Chances are, you can model them all using a single Fruit class.

Encapsulate the concept that varies.

Ciao,
Sheldon.

Sorry for the obfuscation, I am just being paranoid. I am modeling
ingredients to a recipe for making beer.

There are five things that go into beer: fermentables, hops, extras,
yeast and water. Each ingredient provides different things to a
recipe. For example, the join model between recipes and fermentables
contains an amount, potential and color. Hops provide boil time,
amount, bitterness and form. Each ingredient has different
information in the join model. Furthermore, if I made a single table
out of all five ingredient types it would have between 60 and 75
columns.

I was able to build a single controller for all 5 ingredients until I
came to the hops. Some of them have different names, so that meant
using a specialized controller just for them. I would like to get all
my ingredients modeled the same way so I can avoid that.

Thanks for the help.
–Dean

6

P.S.: It’s probably a mistake to produce one class per type of fruit.
Chances are, you can model them all using a single Fruit class.

Encapsulate the concept that varies.

Ciao,
Sheldon.

7

Ah, okay. So it sounds like you’d be very well served indeed by a
polymorphic association.

8

On Feb 16, 5:36 am, “Sheldon H.” [email protected] wrote:

Ah, okay. So it sounds like you’d be very well served indeed by a
polymorphic association.

:smiley:

And I will run into the same problem when I go to implement the
Retailers model and who sells which ingredient for how much. Gah!

Could someone tell me what would be involved in creating a polymorphic
join model? I have enough knowledge of Ruby to kludge something
together by copying from the available polymorphic associations.

Is a polymorphic join model actually feasible?

Will anyone else find this useful?

Regards,
–Dean

9

On Feb 18, 7:03 pm, “Dean” [email protected] wrote:

Could someone tell me what would be involved in creating a polymorphic
join model? I have enough knowledge of Ruby to kludge something
together by copying from the available polymorphic associations.

Looks like Evan W. has already implemented this.

I will take a closer look. Thanks to Evan.

–Dean