[RUBY] An active hash that can be treated as data even if it is not in the database


A function that allows you to select a prefecture from the pull-down menu, which is often seen in questionnaires. , You can have the function to post using the form_with method. However, it is easier to use the prefecture if it is managed numerically on the table. In order to be able to manage with numerical values, it is necessary to prepare the prefecture name and the number associated with it in advance. ActiveHash is a convenient function in such cases.

What is Active Hash?

Gem that allows you to handle data without saving it in the database by entering data that basically does not change in the model. Mainly used when you want to display as a pull-down menu in the view.

The official documentation is here

Flow of preparation

  1. Description of Gem
  2. Install Gem
  3. Generate a model

1. Description of Gem

OK on the bottom line of the file


gem 'active_hash'

2. Install Gem

% bundle install

3. Generate a model

%rails g model model name--skip-migration

The model name should be such that the pull-down menus are grouped together. ex) Baseball, soccer, tennis ... When creating a pull-down like, the model name will be sport.

By adding the --skip-migration option, the migration file will not be generated. ActiveHash does not store in the database, so it does not require a migration file.

Hereinafter, the sports pull-down menu will be described as an example.

Flow from description to display

  1. Define and inherit the class
  2. Describe the items in the pull-down menu
  3. Describe the association
  4. Describe validation
  5. Display pull-down menu

4. Define and inherit the class

Change the model created in "3. Model generation" to the following description.


class Sport < ActiveHash::Base
  self.data = []

ActiveRecord methods can be used by inheriting ActiveHash :: Base.

5. Describe the items in the pull-down menu

The contents of the pull-down are hashed into the array.


class Sport < ActiveHash::Base
  self.data = [
    { id: 1, name: '---' },
    { id: 2, name: 'Baseball' },
    { id: 3, name: 'Soccer' },
    { id: 4, name: 'Tennis' }

6. Describe the association

Below is an explanation of the premise that there is already a table to store another post.


class Post < ApplicationRecord
  extend ActiveHash::Associations::ActiveRecordExtensions
    belongs_to_active_hash :sport

ʻExtend ActiveHash :: Associations :: ActiveRecordExtensions allows you to use the belongs_to_active_hash method`.

There is no need to describe the association in the sport model.

* Note that the description is different from the normal association </ font>

7. Describe validation


class Post < ApplicationRecord
  extend ActiveHash::Associations::ActiveRecordExtensions
    belongs_to_active_hash :sport

  validates :sport_id, presence: true #Unable to save empty post

  validates :sport_id, numericality: { other_than: 1 } 
                        #The pull-down selection is "--Cannot be saved when

8. Display pull-down menu

collection_select method

collection_select(Column name to be saved,Array of objects,Items stored in columns,Column name displayed in the options,option,html option)
collection_select(:sport_id, Sport.all, :id, :name, {}, {class:"sport-select"})

Column name to be saved: In which column of the table to save. Array of objects: If you want to display all the hashes of the array, you can use .all. Items saved in column: I want to save the part of ʻapp / models / sport.rb that was set to ʻid: in the column. Column name displayed in the options: Display the part of ʻapp / models / sport.rbthat was set asname:` in the pull-down menu. Optional: as needed html options: class name, etc.


Anyway, the collection_select method has too many arguments, which can be confusing ...

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