Joining tables but not on the default ID field

Rails
1

I’ve got a working app, at its core I have a rake task that pulls in the
resort data from a CSV file (which a data provider will give me
annually). Thanks to the help here it’s all working fine. I think I’ve
made a basic error in the architecture of the app though and I’d like to
put it right at this early stage.

In short my data providers CSV file contains a serial_number field which
looks like this “574338”. You can see my existing app records it in a
serial_number field of the Resort.

I have adverts too such with HABTM on resorts ↔ adverts, as I say it’s
al working as it but I think that what I need to do here is alter the
join table so that it links adverts to resorts on serial_number and not
on the resort ID. My concern here is that I want to be using the same
key field for resorts as my data provider and that’s the serial_number.

So - how do I do it? I made several attempts, but it all gets quite
confusing, quite quickly.

I’d be very grateful for help, a lot of code with line numbers pasted
here. I’m guessing that the secret sauce is in lines, 5, 90, 196 and 197
(unsure if I have to touch the resort or advert migrations).

I’ve pastied the routes file as well for good measure.

http://pastie.org/581103

Be grateful for help here :-).

bb

2

I guess you can do it as long as you explicitly specify the foreign key
in your model.

For example, let us now try and join Category Table and Subcategory
Table using ‘serial_no’ instead of ‘id’.

class Category < ActiveRecord::Base
has_many :subcategories, :foreign_key => “serial_no”
end

class Subcategory < ActiveRecord::Base
belongs_to :category, :foreign_key => “serial_no”
end

3

So if I’ve understood you correctly,

I could just edit this

in advert.rb
has_and_belongs_to_many :resorts

in resort.rb
has_and_belongs_to_many :adverts

to include , :foreign_key => “serial_number”

Which one (or both) do I specify the foreign key on and importantly does
the join table migration work as it is?

4

On Aug 12, 12:38 pm, bingo bob [email protected]
wrote:

to include , :foreign_key => “serial_number”

Which one (or both) do I specify the foreign key on and importantly does
the join table migration work as it is?

a bit more complicated with a has_and_belongs_to_many - there’s
a :foreign_key and :association_foreign_key (one for each ‘side’ -
check the docs). not sure what you mean about the migration working.

Fred

5

Hi Fred,

I mean lines 196 / 197 in the pastie here http://pastie.org/581103 - re
the migration that sets up the join table.

Do you see what I’m trying to achieve? The serial_number field is unique
and each resort has one.

bb

6

ahhh, ok, maybe I can go about this a different way or maybe just forget
about it !
Strange, I thought this might be doable and in these circumstances the
best thing to do.

7

On Aug 12, 1:03 pm, bingo bob [email protected]
wrote:

Hi Fred,

I mean lines 196 / 197 in the pastie herehttp://pastie.org/581103- re
the migration that sets up the join table.

Do you see what I’m trying to achieve? The serial_number field is unique
and each resort has one.

I’ve realised what you’re trying to do - you want the columns in the
join tables to refer to a column other than the id column in the
parent tables. I’m not sure habtm supports that.

Fred