Validate and save json data into database using dry-rb gems and without using active record.

create_individual_details.rb

class CreateIndividualDetails < ActiveRecord::Migration[6.0]
  def change
    create_table :individual_details do |t|
      t.string :detail_type
      t.json :individual_data
      t.integer :user_id

      t.timestamps
    end
    add_index :individual_details, :user_id, unique: true
  end
end

form.html.erb

<%= form_tag('/post_url', method: 'post', id: 'details_form') do %>
  <% if @form_tag.errors.present? %>
    <div id="errors" class="panel panel-danger">
      <div class="panel-body">
        <ul>
          <% @form_obj.errors.each do |key, msg| %>
            <% msg.each do |m| %>
              <li><%= key.to_s.humanize %> - <%= m %></li>
            <% end %>
          <% end %>
        </ul>
      </div>
     </div>  
  <% end %>

  <div>
    <%= label_tag "individual[full_name]", "First Name" %>
    <%= text_field_tag "individual[full_name]", @form_obj.full_name %>
  </div>
  <div>
    <%= label_tag "individual[email]", 'Email' %>
    <%= text_field_tag "individual[email]", @form_obj.email %>
  </div>
  <div>
    <%= label_tag "individual[postal_code]", 'Zip Code' %>
    <%= text_field_tag "individual[postal_code]", @form_obj.postal_code %>
  </div>
  <div>
    <%= label_tag "individual[date_of_birth]", 'Date of Birth' %>
    <%= date_field_tag "individual[date_of_birth]", @form_obj.date_of_birth %>
  </div>

  <%= submit_tag 'Submit Details', class: 'btn btn-primary' %>
<% end %>

Gemfile

source 'https://rubygems.org'
ruby '2.6.5'

gem 'dry-initializer'
gem 'dry-struct'
gem 'dry-types'
gem 'dry-validation'

individual_controller.rb

class IndividualController < ApplicationController
  def new
    @form_obj = IndividualForm.new
  end
  
  def create
    @form_obj = IndividualForm.new(
      onboarding_params.to_h.deep_symbolize_keys
    )
    if @form_obj.save(current_user.id)
      redirect_to root_path, alert: 'Onboarding data has been successfully saved.'
    else
      render :new
    end
  end
end

individual_form.rb

module Payments
  class IndividualForm < Dry::Struct
    attr_accessor :record, :errors
  
    attribute :full_name, Types::String.optional.default(nil)
    attribute :email, Types::String.optional.default(nil)
    attribute :postal_code, Types::String.optional.default(nil)
    attribute :date_of_birth, Types::String.optional.default(nil)
    
    def save(user_id)
      attributes = to_h
      @record = Payments::IndividualValidation.new.call(attributes)
      @errors = @record.errors.to_h
      return false unless @errors.empty?
      save_response(@record.to_h, user_id)
    end

    private

    def save_response(obj, user_id)
      record = IndividualDetail.new
      record.user_id = user_id
      record.individual_data = obj
      record.save!
    end
  end
end

individual_validation.rb

module Payments
  class IndividualValidation < Dry::Validation::Contract
    MINIMUM_AGE = 18
    DIGITS_LENGTH = 6
    required(:full_name).filled(:string)
    required(:email).filled(:string)
    required(:postal_code).filled(:integer)
    required(:date_of_birth).filled(:date)
    
    rule(:postal_code) do
      key.failure(I18n.t('individual.postal_code.length')) if key? && value.digits.count < DIGITS_LENGTH
    end

    rule(:date_of_birth) do
      if (value < Date.today) && ((Date.today - value).to_i / 365) <= MINIMUM_AGE
        key.failure(I18n.t('individual.date_of_birth.minor'))
      end
    end
  end
end

this is a good use of struct and validation 👍

The only I would suggest here is to separate data (Payments::IndividualForm) and runtime logic (its #save etc methods). How a bit of data is saved or validated isn't really a responsibility of that data, and it makes reusing that logic harder, while also coupling data structure and operations.

For example, here I would leave Payments::IndividualForm is just a data struct with no methods attached to it, and extract validation and saving into their own command-like classes - this will make them reusable with other data structures that you might have in the future.

This can also be paired nicely with using rom-rb instead of ActiveRecord, if you want to go all-in on new concepts :)