[RUBY] I was addicted to the record of the associated model

Work environment

Rails '5.2.3' Ruby '2.7.1' PostgreSQL

What I was addicted to

I tried to delete the registered item while checking the operation in the local environment while creating the review sharing application.

ActiveRecord::InvalidForeignKey in ItemsController#destroy PG::ForeignKeyViolation: ERROR: update or delete on table "reviews" violates foreign key constraint "fk_rails_5350d1b47c" on table "comments" DETAIL: Key (id)=(6) is still referenced from table "comments". : DELETE FROM "reviews" WHERE "reviews"."id" = $1

Error ,. There is no comment table called ʻon table" comments "`. I was worried, but when I first created the app, I was thinking of creating a comment function for review, but isn't it necessary to have a one-sided comment function for review? There was a past that I stopped implementing it because I thought (I forgot). However, I thought that the comments table was deleted and I was addicted to it.

Addictive background

The relationship is that an item has multiple reviews while creating a review sharing app in Rails.


has_many :category_items, dependent: :destroy
has_many :categories, through: :category_items
has_many :reviews, dependent: :destroy
has_many :favorites, dependent: :destroy
accepts_nested_attributes_for :category_items


belongs_to :user
belongs_to :item
has_many  :notifications, dependent: :destroy

Think about what caused the error

From here, it is a consideration that a beginner thought. I would appreciate it if you could point out if it is different. At the same time you try to delete the item, the review associated with the item will also be deleted. has_many: reviews, dependent:: destroy This. So this time, item is deleted → review disappears → comment table remains


has_many  :comments, dependent: :destroy

I thought that it was a phenomenon that review could not be erased because there was no description, so item could not be erased.

So how to deal with this error

First of all, it is a confirmation that the comments table really remains. Updated db / schema.rb with rails db: schema: dump. Then look at schema.rb


 create_table "comments", force: :cascade do |t|

I had comments ... Delete unnecessary tables.

comments table deletion

Create a migration file and write the following

def change
 drop_table :comments

Goodbye with rails db: migrate. Now you can delete the review for both items! !!


I wrote it for a long time with just this, but the lesson I learned in this case is that machines will not betray, and it is the first person to doubt. The assumption is not good. It's my first post, so there are a lot of things I'm not sure about, but I hope it helps someone.

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