Rails associations in one table (belongs_to :region, has_many :regions)

Question

I'm trying to create simple geo-model with tree-structure with Rails4. Every region has one parent region and can have many children regions.

class Region < ActiveRecord::Base
has_many :regions, belongs_to :region, dependent: :destroy
end

Schema:

create_table "regions", force: true do |t|
  t.string   "name"
  t.string   "description"
  t.integer  "region_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

Unfortunatelly, such code is not working. What should i do?

score 1 · Answer 1 · answered Aug 22 '13 at 10:18

1

I think, you are looking for a self join relationship. Try this :

class Region < ActiveRecord::Base
  has_many :child_regions, class_name "Region", foreign_key: "parent_id" dependent:   :destroy      
  belongs_to :parent, class_name: "Region"  
end

You should have a parent_id in your schema as well. Thanks

answered Aug 22 '13 at 10:18

Rails Guy

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Thanks, but what difference between this solution and solution from @maddening? – Pavel Tkackenko Aug 22 '13 at 10:25
No difference except in this case you have `child_regions` and `parent` methods instead of `regions` and `region`. It's also a bit more complicated... – Marek Lipka Aug 22 '13 at 10:34

score 0 · Answer 2 · answered Aug 22 '13 at 10:13

0

class Region < ActiveRecord::Base
  has_many :regions, dependent: :destroy
  belongs_to :region
end

Of course you also need region_id integer column in your regions table.

answered Aug 22 '13 at 10:13

Marek Lipka

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Sorry, I forgot about my db schema (added to topic). I already have region_id – Pavel Tkackenko Aug 22 '13 at 10:16

score 0 · Accepted Answer · answered Aug 22 '13 at 10:16

I assume that Rails4 works just as Rails3 in this case:

class Region < ActiveRecord::Base
    has_many   :regions, dependent: :destroy
    belongs_to :region
end

has_many and belongs_to are class/singleton methods of Region. Aa such you cannot use one of them as a parameter to the other method.

Rails associations in one table (belongs_to :region, has_many :regions)

3 Answers3