#Rails migration / Remove unique index / Mysql2::Error: Cannot drop index 'index_xxx_on_yyy_id': needed in a foreign key constraint

I dont know its best way or wrong way
but it seems to work

model Annotation = DB table schema info

Wanna delete UNIQUE index

# == Schema Information
#
# Table name: books
# user_id                          :bigint           not null
#
# Indexes
#
- # index_books_on_user_id (user_id)
+ # index_books_on_user_id (user_id) UNIQUE
#
#
# Foreign Keys
#  fk_rails_...  (user_id => sims.id)
#

Model

class Book < ApplicationRecord
  belongs_to :user
end

Fail Migration

class RemoveUniqueIndexUserIdFromBoook < ActiveRecord::Migration[5.2]
  def change
    # Mysql2::Error: Cannot drop index 'index_books_on_user_id': needed in a foreign key constraint
    remove_index :books, :user_id
  end
end

Succeed Migration

class RemoveUniqueIndexUserIdFromBoook < ActiveRecord::Migration[5.2]
  def change
    # Anti migration error
    # Mysql2::Error: Cannot drop index 'index_books_on_user_id': needed in a foreign key constraint
    remove_foreign_key :books, name: "fk_rails_80340687ab"
    remove_index :books, :user_id
    add_index :books, :user_id
    add_foreign_key :books, :users
  end
end

Original by Github issue

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