JSON Typed Attributes

This skill helps you work with JSON-backed attributes in Rails models using the StoreJsonAttributes concern. It provides type casting, validation support, and seamless form integration.

When to Use

• You need flexible data storage without creating separate database columns
• You want to store structured data (like configuration, metadata, or dynamic fields) in a JSON column
• You need proper type casting for JSON attributes (numbers, dates, booleans, arrays)
• You want to validate JSON-backed attributes like regular ActiveRecord attributes
• You need JSON attributes to work seamlessly with Rails forms

Setup

1. Ensure JSON Column Exists

Your model must have a JSON column to store the attributes. Common names are data, metadata, or settings:

# In migration
add_column :table_name, :data, :jsonb, default: {}

2. Include the Concern

class YourModel < ApplicationRecord
  include StoreJsonAttributes
end

3. Define Typed Attributes

Use store_typed_attributes to define attributes with automatic type casting:

store_typed_attributes [:attribute_name], type: :type_name, field: :json_column_name

Supported Types

String

store_typed_attributes %i[timeline status], type: :string, field: :data

• Casts values to strings
• Returns nil for blank values
• Example usage:

  record.timeline = "30 Days"
  record.timeline # => "30 Days"

Integer

store_typed_attributes %i[age count quantity], type: :integer, field: :data

• Casts values to integers
• Automatically strips commas and spaces from input ("1,000" → 1000)
• Returns nil for invalid values
• Example usage:

  record.quantity = "1,500"
  record.quantity # => 1500

Decimal

store_typed_attributes %i[price revenue percentage], type: :decimal, field: :data

• Casts values to BigDecimal
• Automatically strips commas and spaces from input
• Preserves precision
• Example usage:

  record.price = "1,234.56"
  record.price # => BigDecimal("1234.56")

Boolean

store_typed_attributes %i[active enabled verified], type: :boolean, field: :data

• Creates predicate methods (ending in ?)
• Casts truthy/falsy values correctly
• Example usage:

  record.active = "1"
  record.active? # => true
  
  record.active = "0"
  record.active? # => false

Date

store_typed_attributes %i[started_at completed_at], type: :date, field: :data

• Casts strings to Date objects
• Handles various date formats
• Example usage:

  record.started_at = "2026-02-04"
  record.started_at # => Date object
  record.started_at.strftime("%B %d, %Y") # => "February 04, 2026"

Array

store_typed_attributes %i[categories tags], type: :array, field: :data

• Always returns an array (empty array if nil)
• Automatically removes blank values with compact_blank
• Example usage:

  record.categories = ["Revenue Generation", "Operations Management"]
  record.categories # => ["Revenue Generation", "Operations Management"]
  
  record.categories = ["", "Valid", nil, "Another"]
  record.categories # => ["Valid", "Another"]

Text

store_typed_attributes %i[notes description], type: :text, field: :data

• Similar to string but intended for longer content
• Creates predicate method (ending in ?)
• Example usage:

  record.notes = "Long text content..."
  record.notes? # => true (if present)

Complete Example

# frozen_string_literal: true

class CBPComponents::KeyQuestion < CoreBusinessPresentationComponent
  CATEGORIES = [
    'Revenue Generation',
    'Operations Management',
    'Organizational Development',
    'Financial Management',
    'Ministry',
    'Personal Issue',
  ].freeze

  TIMELINES = ['30 Days', '90 Days', '180 Days', '1 Year', 'More than 1 Year'].freeze

  # Define JSON-backed typed attributes
  store_typed_attributes %i[timeline], type: :string, field: :data
  store_typed_attributes %i[categories], type: :array, field: :data

  # Add validations like any other attribute
  validates :timeline, inclusion: { in: TIMELINES, allow_blank: true }
  validates :categories, inclusion: { in: CATEGORIES }, allow_blank: true

  # Use in strong parameters
  private

  def base_params
    super.concat([:timeline, :summary, categories: []])
  end
end

Working with Forms

JSON-backed attributes work seamlessly with Rails form helpers:

Simple Fields

= form.text_field :timeline
= form.number_field :quantity
= form.check_box :active

Array Fields (Checkboxes)

- CATEGORIES.each do |category|
  = form.check_box :categories,
    { multiple: true, checked: form.object.categories.include?(category) },
    category,
    nil
  = category

Select Fields

= form.select :timeline,
  options_for_select(TIMELINES, form.object.timeline),
  { include_blank: "Select timeline" }

Adding Validations

Validate JSON-backed attributes like regular attributes:

# Presence
validates :timeline, presence: true

# Inclusion
validates :timeline, inclusion: { in: TIMELINES }

# Length
validates :categories, length: { minimum: 1, message: "must select at least one" }

# Custom validation
validate :categories_must_be_valid

private

def categories_must_be_valid
  invalid_categories = categories - CATEGORIES
  if invalid_categories.any?
    errors.add(:categories, "contains invalid categories: #{invalid_categories.join(', ')}")
  end
end

# Numericality
validates :quantity, numericality: { greater_than: 0, allow_nil: true }

# Format
validates :status, format: { with: /\A[A-Z][a-z]+\z/, allow_blank: true }

Strong Parameters

Always include JSON-backed attributes in your strong parameters:

# For simple types (string, integer, decimal, boolean, date)
params.require(:model).permit(:timeline, :quantity, :active, :started_at)

# For arrays, use array syntax
params.require(:model).permit(:timeline, categories: [])

Multiple JSON Fields

You can use different JSON fields for different concerns:

class Product < ApplicationRecord
  # Pricing data
  store_typed_attributes %i[base_price discount_percentage], type: :decimal, field: :pricing_data

  # Inventory data
  store_typed_attributes %i[quantity threshold], type: :integer, field: :inventory_data

  # Feature flags
  store_typed_attributes %i[featured new_arrival on_sale], type: :boolean, field: :flags
end

Common Patterns

Constants for Validation

Define constants for valid values:

STATUSES = %w[pending approved rejected].freeze
PRIORITIES = %w[low medium high urgent].freeze

store_typed_attributes %i[status], type: :string, field: :data
store_typed_attributes %i[priority], type: :string, field: :data

validates :status, inclusion: { in: STATUSES, allow_blank: true }
validates :priority, inclusion: { in: PRIORITIES, allow_blank: true }

Default Values

Set defaults in initializer or after_initialize:

after_initialize :set_defaults, if: :new_record?

private

def set_defaults
  self.categories ||= []
  self.timeline ||= '90 Days'
  self.active = true if active.nil?
end

Scopes and Queries

Query JSON attributes using PostgreSQL JSON operators:

# Find records with specific value
scope :with_timeline, ->(timeline) {
  where("data->>'timeline' = ?", timeline)
}

# Find records where array contains value
scope :with_category, ->(category) {
  where("data->'categories' ? :category", category: category)
}

# Find records with any of multiple values
scope :with_any_category, ->(categories) {
  where("data->'categories' ?| array[:categories]", categories: categories)
}

Best Practices

1. Always specify the field name - Makes it clear where data is stored

   store_typed_attributes %i[timeline], type: :string, field: :data

2. Use arrays for multi-select data - Automatically handles blank values

   store_typed_attributes %i[categories], type: :array, field: :data

3. Define constants for valid values - Makes validations and forms easier

   TIMELINES = ['30 Days', '90 Days', '180 Days'].freeze
   validates :timeline, inclusion: { in: TIMELINES, allow_blank: true }

4. Add validations - JSON attributes should be validated like any other attribute

   validates :quantity, numericality: { greater_than: 0, allow_nil: true }

5. Use appropriate types - Choose the type that matches your data

   • Use :decimal for money/percentages (not :integer)
   • Use :array for multi-select (automatically removes blanks)
   • Use :boolean for flags (creates predicate methods)

6. Include in strong parameters - Don't forget array syntax for array types

   params.require(:model).permit(:timeline, categories: [])

7. Consider indexing - For frequently queried JSON attributes, add GIN indexes

   add_index :table_name, :data, using: :gin

Troubleshooting

Attribute not persisting

• Ensure the JSON column exists in the database
• Check that the field name matches: field: :data
• Verify strong parameters include the attribute

Type casting not working

• Verify the type is spelled correctly: :integer, :decimal, :string, etc.
• For arrays, ensure you're setting an array value
• For booleans, use the predicate method: record.active?

Form not displaying correct values

• For arrays, check that you're using multiple: true and checking inclusion
• For selects, use options_for_select with the current value
• Ensure the getter method returns the expected type

Validation failing

• Check that the attribute is included in strong parameters
• Verify constants match the expected values exactly
• For arrays, remember blank values are automatically removed