Nested forms for children and relationships

nested.rb

# Models

class Child
  has_many :relationships
end

class RelationType
  has_many :relationships
end

class User
  has_many :relationships
end

class Relationship
  belongs_to :relation_type
  belongs_to :user
  belongs_to :child

  accepts_nested_attributes_for :relationships
end


# Controller

class RelationshipsController
  def new
    @relationship = current_user.relationships.new
  end

  def create
    @relationship = current_user.relationships.new(params[:relationship])

    @relationship.save
  end
end

view.html.erb

<!-- New child -->
<%= form_for @relationship do |f| %>
  <%= f.input :relation_type %> # defaults to a select
  <%= f.simple_fields_for :child do |cf| %>
    <%= cf.input :name %>
    <%=  etc %>
  <% end %>
<% end %>

<!-- Child already exists -->
<%= form_for @relationship do |f| %>
  <%= f.input :relation_type %> # defaults to a select
  <%= f.input :child %>
<% end %>