[RUBY] How to delete data with foreign key

environment

This article uses Ruby 2.6.5 installed on macOS Catalina 10.15.6.

Premise

We have created three models and the situation is as follows.

User / User Report / Report Comment / User-report association table

The following error occurred when deleting a report with comments.

Error occurred

ActiveRecord::InvalidForeignKey in ReportsController#destroy Foreign key error スクリーンショット 2020-10-22 10.00.46.png

Think about the solution to what is the cause.

Cause

When deleting a report, it is determined that the cause is that the user in the comment table and the id value of the report are lost. (Due to foreign key constraints) I want to be able to delete comments if the user and report ids are no longer associated.

solution

dependent: :Describe destroy in User model and Report model.


 With this description, when you delete the parent model (Report), you can also delete the "child model (Comment)" associated with the parent model. "

## Verification


#### **`app/models/user.rb`**
```ruby

class User < ApplicationRecord
  has_many :reports
  has_many :comments, dependent: :destroy
end

app/models/report.rb


class Report < ApplicationRecord
  belongs_to :user
  has_many :comments, dependent: :destroy
end

Completed without incident! that's all. I hope it helps those who have similar problems or are hitting a wall!

reference

I referred to the following, so if you want to understand the contents more deeply, please take a look! https://qiita.com/Ushinji/items/650fa295a3054d2fe582 https://qiita.com/ITmanbow/items/2170ccaceafd5d401df8 https://qiita.com/Tsh-43879562/items/fbc968453a7063776637

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