Ruby version: 2.6.3 / Rails version: 6.0.3

A model UserAttribute (hb_project/app/models/user_attribute.rb) allows to store custom attributes for a User. The types Boolean and String are supported through the property field_type.
A model User (hb_project/app/models/user.rb) represents the users, with a role property to defined whether they are a basic user or an admin.
A model UserAttributeValue (hb_project/app/models/user_attribute_value.rb) has been created to act as a join model between User and UserAttribute. A many-to-many relation links them all together. This is the place where the specific values of the custom attributes will be stored for the users.

The same logic applies for Event, EventAttribute and EventAttributeValue. I could have used only one class for EventAttribute and UserAttribute but since both could evolve differently I prefered to keep the two features separated.

As requested by the exercise, the following criterias must be supported:

• Admin manages the global User custom attributes
  Done through hb_project/test/models/user_attribute_test.rb
• Admin manages a specific Event’s custom attributes
  Done through hb_project/test/models/event_attribute_test.rb
• Admin makes a custom attribute optional/required on the User profile
  Done through hb_project/test/models/user_attribute_test.rb
• Admin makes a custom attribute optional/required on the User signup form
  Done through hb_project/test/models/user_attribute_test.rb
• Admin makes a custom attribute optional/required on a specific Event Registration form
  Done through hb_project/test/models/event_attribute_test.rb
• User fills in a custom attribute on his profile
  Done through hb_project/test/models/user_test.rb
• User fills in a custom attribute on the signup form
  Done through hb_project/test/models/user_test.rb
• User fills in a custom attribute on an Event Registration form
  Done through hb_project/test/models/event_test.rb
• User reads his custom attributes on his profile
  Done through hb_project/test/models/user_test.rb
• Admin reads an Event registration’s custom attributes
  Done through hb_project/test/models/event_test.rb

All those tests can be launched in a Docker container with docker/run rails test -v. The command docker/setup is also available for a first setup.
The default test framework provided by Rails 6 was used.

For the moment, everything highly relies on models. On a second step it could be good to abstract some logic into service classes.