[Rails] Articles for beginners to organize and understand the flow of form_with

Introduction

At the beginning of Rails learning, I could not understand the flow of form_with, so I will summarize it. Rails 5.2.4.

Summary first

I'm sure there are people who say, "Get together quickly!", So I'll summarize the flow first.

Brief commentary

There is a User model and a Post model.

** ① Display the view page (new.html.erb) with new action ** When a request to call the new action is made, the new post page of post is displayed first. ※image

** ② Pass the @post instance created by the new action to the view **

post_controller.rb

class PostsController < ApplicationController
~~
  def new
    @post = Post.new #Generated here@post is new.html.Passed to erb
  end
~~

** ③ Enter a value in the instance property and submit **

** ④ Call the create action ** As you can see in the image above, when you click the submit button (submit form_with), form_with will call the create action.

• The form_with helper method is a convenient child that looks at the properties of the passed instance (@post in this case) and decides whether to skip to create or update.

form_with is thinking

- @post is empty → I'm making it for the first time! Then create!
- @post is not empty → I want to change it! Then update!

** ⑤ Call the post_params method **

post_controller.rb

class PostsController < ApplicationController
~~
  def create
    #The create action is called and Post.create(post_params)Is executed → post_params is called
    Post.create(post_params) 
    redirect_to root_path
  end

  private
  def post_params 
    params.require(:post).permit(:title, :content).merge(user_id: current_user.id)
  end
~~

** ⑥ Of the values received by params, specify the value received by permit (permit) **

State of the value received by params

[1] pry(#<PostsController>)> params
=> <ActionController::Parameters {"utf8"=>"✓", "authenticity_token"=>"oLGgLMTcqSPi7cbK9j1wFhH5rqiwXYO7GyRoZcZFZe6Y5VdbHrWCOyeo37kgW/bsl+eANQrz7p/lAzZMnAS8Gg==", 
"post"=>{"title"=>"What I learned today", "content"=>"form_with is a wise child!"}, 
"commit"=>"Post", "exept"=>:index, "controller"=>"posts", "action"=>"create"} permitted: false>

Since it is hard to see, the line breaks at a position that is not originally there, but usually it returns in one line.

" post "=> {" title "=>" What I learned today "," content "=>" form_with is a wise child! "}, Is the value handled by post_params.

If you do not allow the values received by permit, unintended values may be stored in the table, so it is almost mandatory to specify.

** ⑦ Create Post with the value of post_params (save to table if successful) ** Post.create will be done with the value returned by the post_params method, so It is in the same state as below.

  def create
    Post.create(title: "What I learned today", content: "form_with is a wise child!", user_id: 1) 
    redirect_to root_path
  end

After confirming this flow, if you look at the image at the beginning again, you will deepen your understanding!

in conclusion

The differences between form_tag and form_for are summarized in this article. How to write form_with / form_for / form_tag in [Rails] haml

I would appreciate it if you could point out any mistakes.