[RUBY] [Rails / Uniqueness constraint] How to check model validation on the console / Uniqueness constraint for multiple columns


This validation can be achieved by using "uniqueness constraint".

This time it is a record of the operation on the console launched with rails c to see if this is implemented properly.


This code


class Permission < ApplicationRecord
  belongs_to :user
  belongs_to :task

  validates :user_id, uniqueness: { scope: :task_id }

By the way, this is a constraint on the application, and to be exact, it is necessary to set a constraint on the DB side as well (<a href-"https://railsguides.jp/active_record_validations.html#uniqueness:title"> Rails guide < From / a>). However, I do not understand it yet, so I will omit it this time.

Commands entered on the console

I wanted to check the uniqueness constraint, so I executed the code according to the following flow.

I launched the console in the terminal and checked.


$ rails c

[1] > permission = Permission.find(1)
=> #<Permission:*** id: 1, user_id: 1, task_id: 1, ***>

[2] > new.valid?
=> true

It has become true ... I thought about the cause and changed the command.

Cause and command change

[Cause] ▶ "find" is an ActiveRecord method that searches for existing records ▶ If you save this, will it look like an overwrite save?

【Change】 ▶ Directly type user_id and task_id


$ rails c

[1] > Permission.find(1)
=> #<Permission:*** id: 1, user_id: 1, task_id: 1, ***>

[2] > permission = Permission.new(user_id: 1, task_id: 1)
=> #<Permission:*** id: nil, user_id: 1, task_id: 1, ***>

[3] > permission.valid?
=> false

[4] > permission.errors.full_messages
=> "User has already been taken"

I was able to confirm that it was completely false.


I was a little addicted to it, but I managed to get over it. To really understand, you need to know what's working behind save and valid.

I still have a lot to study, but I will keep it down one by one.

Reference article

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