datamapper prob1

gistfile1.txt

class Feed
  include DataMapper::Resource

  property :id,    Serial
  property :title, String, :key => true
  property :url,   Text

  has n, :feed_posts
  has n, :posts, :through => feed_posts
  
end

class FeedPost
  include DataMapper::Resource
  
  property  :id,    Serial
  property  :feed_title, String,  :key=>true, :required => true
  property  :post_title, String,  :key=>true, :required => true
  
  belongs_to  :feed
  belongs_to  :post
end

class Post
  include DataMapper::Resource

  property  :id,          Serial
  property  :title,       String, :key=> true
  property  :url,         Text
  property  :timestamp,   DateTime
  property  :content_raw, Text

  has 1, :feed_post
  has 1, :feed, :through => feed_post
end

Produces 'Cannot find the child_model FeedPost for Feed in feed_posts (NameError)'
Why ?