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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

Sponsored by Evil Martians

Why should I wrap my JSON columns?

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 single-repsponsibility 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

Getting started

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 re-assigned; Rails doesn't track mutations of objects. For example: self.my_stored_models = my_stored_models.map(&:as_json)

Documentation

  1. Installation
  2. StoreModel::Model API:
  1. Array of stored models
  2. One of
  3. Alternatives
  4. Defining custom types

License

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