Has_many :through

Rails
1

Hello,
I have 4 tables Provinces, Districts, Cities and Municipalities.
A Province has many Districts. A district has many Cities, and a City
has
many Municipalities.

With this code :

class Province < ActiveRecord::Base

relationship

has_many :districts
has_many :cities, :through => :districts
end

I can do this :
@province = Province.find(:first)
@province.cities.first.name

I would like to go one step further and be able to do
@province.districts.first.name

Is it possible?
How can I do that?

Thanks for sharing your experience.
Thomas.

2

Oups!What I would like to do is :
@province.municipalities.first.name

Thanks for pointing that out, Jon.

3

Thomas B. wrote:

has_many :cities, :through => :districts
How can I do that?

Thanks for sharing your experience.
Thomas.

Unless there’s a typo in your code somewhere, I don’t think there’s any
reason that you shouldn’t be able to do that now, with what you’ve
already got.

–
http://www.5valleys.com/

4

AR doesn’t support nested has_many :through. You can try following :

class Province < ActiveRecord::Base

relationship

has_many :districts
has_many :cities, :through => :districts, :include =>
:municipalities

def municipalities
self.cities.map(&:municipalities)
end
end

Please note that this could nuke your memory if you’re dealing with
large datasets.

On 8/6/07, Thomas B. [email protected] wrote:

Hello,
has_many :cities, :through => :districts
How can I do that?
http://www.5valleys.com/

–
Cheers!

5

Although it does with the has_many_through plugin [http://
code.torchbox.com/svn/rails/plugins/nested_has_many_through/] :slight_smile:

6

Thanks for your answer!Thomas.

7

I wouldn’t really suggest using that plugin if you’re not on stable
rails release.

On 8/7/07, Aaron P. [email protected] wrote:

has_many :cities, :through => :districts, :include => :municipalities

Thomas B. wrote:

has_many :districts
Is it possible?
http://www.5valleys.com/

–
Cheers!

  • Pratikhttp://m.onkey.org

–
Cheers!