Rails has_and_belongs_to_many with specific key

Question

I has two models

class Fellow < ApplicationRecord
  has_and_belongs_to_many :skills
end

class Skill < ApplicationRecord
  has_and_belongs_to_many :fellows
end

One fellow can have some skills, and one skill can be learned by some fellows. So I have third table

class CreateFellowsSkills < ActiveRecord::Migration[5.0]
  def change
    create_table :fellows_skills, id:false do |t|
      t.belongs_to :skill, index: true
      t.belongs_to :fellow, index: true
    end
  end
end

I want to use method: fellow.skills That invoke such SQL:

SELECT "skills".* FROM "skills" INNER JOIN "fellows_skills" ON "skills"."id" = "fellows_skills"."skill_id" WHERE "fellows_skills"."fellow_id" = $1

The problem: I want to use field skill_id in table skills instead of id, so the query should be such:

SELECT "skills".* FROM "skills" INNER JOIN "fellows_skills" ON "skills"."skill_id" = "fellows_skills"."skill_id" WHERE "fellows_skills"."fellow_id" = $1

I tried to use different options in method has_and_belongs_to_many but the query is still incorrect.

`skill_id` is this a column you have added to `skills` table ? — dp7, Sep 16 '16 at 06:51
Yes, I have primary key ID in table SKILLS, but while FELLOW.SKILLS, I need to use field SKILL_ID — user2572790, Sep 16 '16 at 06:54
You can do this by using foreign_key as `skill_id`. Check this: http://stackoverflow.com/questions/1475088/how-can-i-load-habtm-with-foreign-key-relationships-in-my-fixtures — Gokul, Sep 16 '16 at 06:54

score 1 · Accepted Answer · answered Sep 16 '16 at 06:55

http://cobwwweb.com/why-i-dont-use-has-and-belongs-to-many-in-rails

Instead of habtm, use

class Fellow < ApplicationRecord
  has_many :fellows_skills
  has_many :skills, through :fellows_skills
end

class Skill < ApplicationRecord
  has_many :fellows_skills
  has_many :fellows, through: :fellows_skills
end

class FellowsSkill < ApplicationRecord
  belongs_to :fellow
  belongs_to :skill
end

Furthermore I would suggest naming the third model FellowSkill (dropping the plural on fellow).

score 0 · Answer 2 · answered Sep 19 '16 at 03:33

0

Finally I correct my db scheme and call primary key ID, so I don't need apply any changes now.

answered Sep 19 '16 at 03:33

user2572790

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Rails has_and_belongs_to_many with specific key

2 Answers2