StoreModel gem allows you to wrap JSON-backed DB columns with ActiveModel-like classes.

• 💪 Powered with Attributes API. You can use a number of familiar types or write your own
• 🔧 Works like ActiveModel. Validations, enums and nested attributes work very similar to APIs provided by Rails
• 1️⃣ Follows single responsibility principle. Keep the logic around the data stored in a JSON column separated from the model
• 👷‍♂️ Born in production.

class Configuration
  include StoreModel::Model

  attribute :model, :string
  enum :status, %i[active archived], default: :active

  validates :model, :status, presence: true
end

class Product < ApplicationRecord
  attribute :configuration, Configuration.to_type
end

Imagine that you have a model Product with a jsonb column called configuration. This is how you likely gonna work with this column:

product = Product.find(params[:id])
if product.configuration["model"] == "spaceship"
  product.configuration["color"] = "red"
end
product.save

This approach works fine when you don't have a lot of keys with logic around them and just read the data. However, when you start working with that data more intensively–you may find the code a bit verbose and error-prone.

For instance, try to find a way to validate :model value to be required. Despite of the fact, that you'll have to write this validation by hand, it violates the single-responsibility principle: why parent model (Product) should know about the logic related to a child (Configuration)?

📖 Read more about the motivation in the Wrapping JSON-based ActiveRecord attributes with classes post

Start with creating a class for representing the hash as an object:

class Configuration
  include StoreModel::Model

  attribute :model, :string
  attribute :color, :string
end

Attributes should be defined using Rails Attributes API. There is a number of types available out of the box, and you can always extend the type system.

Register the field in the ActiveRecord model class:

class Product < ApplicationRecord
  attribute :configuration, Configuration.to_type
end

When you're done, the initial snippet could be rewritten in the following way:

product = Product.find(params[:id])
if product.configuration.model == "spaceship"
  product.configuration.color = "red"
end
product.save

Usage note: Rails and assigning Arrays/Hashes to records

• Assigned attributes must be a String, Hash, Array of Hashes, or StoreModel. For example, if the attributes are coming from a controller, be sure to convert any ActionController::Parameters as needed.
• Any changes made to a StoreModel instance requires the attribute be flagged as dirty, either by reassignment (self.my_stored_models = my_stored_models.map(&:as_json)) or by will_change! (self.my_stored_models_will_change!)
• Mixing StoreModel::NestedAttributes into your model will allow you to use accepts_nested_attributes_for in the same way as ActiveRecord.

class Supplier < ActiveRecord::Base
  include StoreModel::NestedAttributes

  has_many :bicycles, dependent: :destroy

  attribute :products, Product.to_array_type

  accepts_nested_attributes_for :bicycles, :products, allow_destroy: true
end

This will allow the form builders to work their magic:

<%= form_with model: @supplier do |form| %>
  <%= form.fields_for :products do |product_fields| %>
    <%= product_fields.text_field :name %>
  <% end %>
<% end %>

Resulting in:

<input type="text" name="supplier[products_attributes][0][name]" id="supplier_products_attributes_0_name">

In the controller:

def create
  @supplier = Supplier.new(supplier_params)
  @supplier.save
end

private

def supplier_params
  params.require(:supplier).permit(products_attributes: [:name])
end

1. Installation
2. StoreModel::Model API:

• Validations
• Enums
• Nested models
• Unknown attributes

3. Array of stored models
4. One of
5. Alternatives
6. Defining custom types
7. Disabling Parent Tracking

Initially sponsored by Evil Martians.

The gem is available as open source under the terms of the MIT License.