Add Convert JSON Field To Hash With Indifferent Access as a Rails TIL

rails/convert-json-field-to-hash-with-indifferent-access.md

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+# Convert JSON Field To Hash With Indifferent Access
+
+Let's say we have an `Event` model whose backing table includes a `JSONB` (or
+`JSON`) field called `details`.
+
+When we access `details` in a Rails context, digging into that nested data we
+have to use string keys throughout. However, we may have existing related code
+that is dealing with this shape of data using symbol keys. This might put us in
+a position where we have to rework a bunch of existing code or do defensive
+coding like `details[:user] || details["user"]`.
+
+To avoid that, we can instead have the `Event` model override `details`
+converting that underlying data to `HashWithIndifferentAccess` before returning
+it.
+
+```ruby
+class Event < ApplicationRecord
+  def details
+    data = super
+    return data if data.nil?
+    
+    case data
+    when Array
+      data.map { |item| item.is_a?(Hash) ? item.with_indifferent_access : item }
+    when Hash
+      data.with_indifferent_access
+    else
+      data
+    end
+  end
+end
+```
+
+With this in place, anywhere in the codebase where we access `details` on an
+instance of `Event` we will be able to use string or symbol keys
+interchangeably.