How to write Rails validation

In the output, I will post how to write validation in Rails.

Validation is the verification that the data is correct.

First in the model


class User < ApplicationRecord

  validates :nickname, presence: true

            :nickname  #Column name

                       presence: true  #Not empty

Then the controller


class UsersController < ApplicationController

  def new
    @user =

  def create
    @user =
      @user.valid?   #here! !! here! !! !!
      redirect_to root_path
      render 'new'


  def user_params

Validation is executed by the valid? method. Returns true if validation is successful.

As a flow, check with validation whether the value is entered when saving what was generated by the new action with the create action. If you use the if statement, save it as @ If empty, alert with render'new'. , ,


= f.text_field :nickname, class: "nickname"
  = @user.errors.full_messages_for(:nickname)[0]

In the view, write the nickname to save and the error message display = @ user.errors.full_messages_for (: nickname) [0] to complete.

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