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copied!<p>I wouldn't suggest a has_one relationship in this case. A User could <code>belongs_to :eye_color</code>, so you can map eyecolors across your users. An EyeColor <code>has_many :users</code>, so that you can do <code>@eye_color.users</code> and get all users with a specific EyeColor. Otherwise you will have to create an EyeColor for every user (or at least the ones with eyes).</p> <p>The reason I'd suggest this over your PersonProperty solution is because it's easier to maintain and because of the performance gain of delegating these kinds of relations to your database.</p> <p><strong>UPDATE:</strong> If dynamic attributes are what you want, I'd suggest to setup your models like this:</p> <pre><code>class Person < ActiveRecord::Base has_many :person_attributes attr_accessible :gender accepts_nested_attributes_for :person_attributes end class PersonAttribute < ActiveRecord::Base belongs_to :person_attribute_type belongs_to :person_attribute_value belongs_to :person attr_accessible :person_id, :person_attribute_value_id end class PersonAttributeValue < ActiveRecord::Base has_many :person_attributes belongs_to :person_attribute_type attr_accessible :value, :person_attribute_type_id end class PersonAttributeType < ActiveRecord::Base has_many :person_attribute_values attr_accessible :name, :type end </code></pre> <p>This way you can do the following:</p> <pre><code>@person_attribute_type = PersonAttributeType.create(:name => 'Eye color', :type => 'string') ['green', 'blue', 'brown'].each do |color| @person_attribute_type.person_attribute.values.build(:value => color) end @person_attribute_type.save @person = Person.new @person_attribute = @person.person_attributes.build @person_attribute.person_attribute_value = @person_attribute_type.person_attribute_values.find(:value => 'green') </code></pre> <p>Of course, you probably won't fill your database through the command line. You will probably be very curious as to how this would work in a form:</p> <pre><code>class PersonController # ... def new @person = Person.new PersonAttributeType.all.each do |type| @person.person_attributes.build(:person_attribute_type = type) end end def create @person = Person.new(params[:person]) if @person.save # ... else # ... end end def edit @person = Person.find(params[:id]) PersonAttributeType.where('id NOT IN (?)', @person.person_attributes.map(&:person_attribute_type_id)).each do |type| @person.person_attributes.build(:person_attribute_type = type) end end # ... </code></pre> <p><em>Now the form, based on Formtastic:</em></p> <pre><code>semantic_form_for @person do |f| f.input :gender, :as => :select, :collection => ['Male', 'Female'] f.semantic_fields_for :person_attributes do |paf| f.input :person_attribute_value, :as => :select, :collection => paf.object.person_attribute_type.person_attributes_values, :label => paf.object.person_attribute_type.name end f.buttons end </code></pre> <p>Mind that this all is untested, so just try to understand what I'm trying to do here.</p> <p><em>BTW, I now realize that the class name Person</em><strong>Attribute</strong> <em>is probably a bit unlucky, because you will have to <code>accepts_nested_attributes_for :person_attributes</code> which would mean you would have to <code>attr_accessible :person_attributes_attributes</code>, but you get my drift I hope.</em></p>

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