has_many关联的唯一性

Question

class User < ApplicationRecord
  has_and_belongs_to_many :profiles

  def add_profile(profile)
    self.profiles << profile unless self.profiles.include?(profile)
  end
end

class Profile < ApplicationRecord
  has_and_belongs_to_many :users
  validates_uniqueness_of :linkedin_id, allow_nil: true
end

For some reason on production I get

ActiveRecord::RecordInvalid: Validation failed: Linkedin has already been taken

on

self.profiles << profile unless self.profiles.include?(profile) line.

And after this I have duplicates in User.profiles records.

What is the problem?

Answer 1

Using has_and_belongs_to_many is probably not the best option here.

If you have the quite common scenario where a user may attach several "profiles" or external OAuth credentials to their account you want a one to many relationship.

This example uses a generic uid column instead of linkedin_id so that you can use the exact same logic for Facebook, Twitter or any other sort of account.

class User < ActiveRecord::Base
  has_many :profiles
end


class Profile < ActiveRecord::Base
  belongs_to :user
end

This guarantees that a profile can only belong to a single user. You may want to add some additional uniqueness constraints.

class AddUserProviderIndexToProfiles < ActiveRecord::Migration
  def change
    add_index(:profiles, [:user_id, :provider], unique: true)
    add_index(:profiles, [:uid, :provider], unique: true)
  end
end

This enforces on the database level that a user can only have one profile with a given provider and that there may only be one profile with for a given :provider, :uid combination. Adding indexes in the database safeguards against race conditions and improves performance.

You will also want a application level validation to avoid the application crashing due to database driver errors!

class Profile < ActiveRecord::Base
  belongs_to :user
  validates_uniqueness_of :uid, scope: :provider
  validates_uniqueness_of :user_id, scope: :provider
end