Get the value of enum saved in DB by Rails with attribute_before_type_cast

Introduction

A reminder of how to get the enum value saved in the DB in Rails with attribute_before_type_cast

environment

• macOS 10.15.6
• Ruby 2.5.7
• Rails 5.2.3

Reference URL

https://api.rubyonrails.org/classes/ActiveRecord/AttributeMethods/BeforeTypeCast.html

https://railsdoc.com/page/options_for_select

https://310nae.com/rails-selectbox/

https://qiita.com/ozackiee/items/17b91e26fad58e147f2e

https://ja.stackoverflow.com/questions/72551/enum-でセレクトボックスを表示させてインデックス番号をdb-に保存したい

What is attribute_before_type_cast?

• You can get the actual value stored in the DB instead of the enum string.
• Instance method that can be used when enum is defined

About the value and actual value of the name definition of enum

Please note that when using enum, the value looks different on Rails and the value saved in DB.

Rails enum is implemented so that it can be handled transparently as a character string (or symbol) in the code notation.

As you can see by hitting SQL directly or looking at the record information saved using the DB GUI client, the number is actually saved instead of the string.

Reference URL: <https://ja.stackoverflow.com/questions/72551/enum-%e3%81%a7%e3%82%bb%e3%83%ac%e3%82%af%e3%83%88 % e3% 83% 9c% e3% 83% 83% e3% 82% af% e3% 82% b9% e3% 82% 92% e8% a1% a8% e7% a4% ba% e3% 81% 95% e3 % 81% 9b% e3% 81% a6% e3% 82% a4% e3% 83% b3% e3% 83% 87% e3% 83% 83% e3% 82% af% e3% 82% b9% e7% 95 % aa% e5% 8f% b7% e3% 82% 92db-% e3% 81% ab% e4% bf% 9d% e5% ad% 98% e3% 81% 97% e3% 81% 9f% e3% 81% 84>

The actual value defined by enum behaves as a name definition on Rails.

sample.rb

#blood type(blood_type)Enum definition

  enum blood_type: {
Type A: 0,
B type: 1,
O type: 2,
AB type: 3,
    #Name definition on Rails:Actual value stored in DB
  }

Operation check

Check the operation based on the following assumptions

• Create name column and blood_type column in Person model
• Define blood_type with enum in Person model

schema.rb

#Name column in Parson model, blood_Create type column
  create_table "persons", force: :cascade do |t|
    t.string "name"
    t.integer "blood_type"
  end

parson.rb

#blood on model_define type with enum
class Person < ApplicationRecord

  enum blood_type: {
Type A: 0,
B type: 1,
O type: 2,
AB type: 3,
  }
end

attribute_before_type_cast method

Check the operation of attribite_before_type_cast using rails console

$ rails console
> person = Person.create(name: "Alice", blood_type: 0) #Create person object,DB save
:name => "Alice"
:blood_type => "Type A"
> person.blood_type #Get the value on rails
"Type A"
> person.blood_type #Get the class of values ​​on rails
String < Object
> person.blood_type_before_type_cast #Get the value of DB
0
> person.blood_type_before_type_cast #Get the class of DB values
Integer < Numeric

attributes, attributes_before_type_cast method

• attributes: Instance method that can get attribute name => value for instance

• attributes_before_type_cast: Before version of attributes. Instance method that can get the actual value on the DB in the form of attribute name => value

Use rails console to see the difference in behavior between attributes and attributes_before_type_cast

$ rails console
> person = Person.create(name: "Alice", blood_type: 0) #Create person object,DB save
:name => "Alice"
:blood_type => "Type A"
> person.attributes #Show name definitions on rails
"name" => "Alice"
"blood_type" => "Type A"
> person.attributes_type_before_type_cast #Display the actual value of DB
"name" => "Alice"
"blood_type" => 0

Example of use

In my case I used it to generate a new post form from the value defined in the enum

#HTML you want to output
<select>
  <option value="1">type1</option>
  <option value="2">type2</option>
  <option value="3">type3</option>
</select>

person.rb

# blood_define type with enum
class Person < ApplicationRecord

  enum blood_type: {
Type A: 0,
B type: 1,
O type: 2,
AB type: 3,
  }
end

persons_controller.rb

#Create person object
def new
  @person = Person.new
end

I am using the value obtained by attirbute_before_type_cast to set the default value (selected: value)

Ruby:new.html.erb

#Form generation from enum value
<%= form_with model: @person local: true do |f| %>
  <%= f.select :blood_type, options_for_select(Person.blood_types, @person.expense_before_type_cast), {}  %>
  <%= f.submit %>
<% end %>

#Each value at the time of form generation
<%= form_with model: @Model name do|f| %>
  <%= f.select :Column name, options_for_select(Model name.Column name複数形, @Model name.Column name_before_type_cast), {}  %>
  <%= f.submit %>
<% end %>

** There is a caveat in the empty brackets ({}) in the select tag **

Be sure to set the empty parentheses {}, in the option part even if you do not set the normal option. Without this empty brace, the HTML options would be ignored, so setting id/class doesn't work! It will be that.

Reference URL: https://310nae.com/rails-selectbox/

# options_for_select syntax
options_for_select(Array or hash of elements,Default value, {option}, {htmloption})

• Option example
• include_blank: true (empty the first line)
• selected: default_value
• HTML option example
• id: id_name (give id)
• class: class_name (grant class)

Summary

• Use attribute_before_type_cast or attributes_before_type_cast to get the actual value saved in the DB when using enum
• The acquisition method is different between the enum name definition value and the actual value.

I've never used enums and I was really into it when creating a portfolio, so it was a good study! If you make a mistake, please comment!