[Rails / ActiveRecord] About the difference between create and create!

Overview

About the ActiveRecord method create that creates a new record. I learned about the difference between create and create!, so I will explain it.

Conclusion: Whether to raise an exception

What is the difference with and without ! ? Conclusion "Whether to raise an exception".

However, it is difficult to understand the "exception". To explain the difference that actually occurs, what changes with or without ! is "Is that red screen appearing?" When processing fails.

In the case of create!

If you set create!, If you get caught in validation, an ActiveRecord :: RecordInvalid exception will occur as shown below, and the familiar screen will be displayed.

Let's follow the actual operation.

The code used this time is as follows (* The description of create action is not recommended).

① Routing

app/config/routes.rb

Rails.application.routes.draw do
  root to: 'comments#index'
  resources :comments, only: [:create]
end

1. Submit an empty value in the form of index.html.erb
2. Request comments # create

② Execute comments # create action

app/controllers/comments_controller.rb

class CommentsController < ApplicationController

  def index
    @comments = Comment.all.order("created_at DESC")
    @comment = Comment.new
  end

  def create
    #Writing this create action is deprecated.
    @comment = Comment.create!(comment_params)
    redirect_to root_path
  end

  private

  def comment_params
    params.require(:comment).permit(:text)
  end
end

1. Load the ActiveRecord method create (new + save)
2. Get parameters with comment_params (text column value is empty)
3. Validation check in the save part of create

③ Validation check with Comment model

app/models/comment.rb

class Comment < ApplicationRecord
  validates :text, presence: true
end

1. It gets stuck in the validation set in the text column
2. Exception occurs because it cannot be saved
3. That red screen is displayed

✔ GIF that follows the above flow

The error screen was displayed firmly.

Without !

Submit the form for the create action below.

app/controllers/comments_controller.rb

def create
  @comment = Comment.create(comment_params) # !Exclude
  redirect_to root_path
end

✔ Operation in this case (GIF)

The error screen does not occur due to exception handling, and you are redirected.

Summary

• ! of create! is a description that raises an exception
• In this case, an ActiveRecord :: RecordInvalid exception is generated and the error screen transitions.
• If there is no ! , the next redirect will be executed as it is without being saved.

reference

• Rails Guide | ActiveRecord Query Interface
• Github self-made code (create-app-1)