gistfile1.rb

require 'rubygems'
require 'dm-core'
gem 'dm-core', '0.10.2'

class Post
  include DataMapper::Resource
   # !> method redefined; discarding old one?
  property :id, Serial
  property :title, String
  
  has n, :comments, :repository => :comments
end

class Comment
  include DataMapper::Resource

  def self.default_repository_name() :comments; end    
 # !> method redefined; discarding old first
  property :id, Serial
  property :body, Text
  
  belongs_to :post, :repository => :default
end

DataMapper::Logger.new($stdout)

DataMapper.setup(:default, 'sqlite3::memory:')
DataMapper.setup(:comments, :adapter => :in_memory)

# This creates a comments table in the sqlite3 db
DataMapper.repository(:default).auto_migrate!
DataMapper.repository(:comments).auto_migrate!

 # !> instance variable @field_types not initialized
post = Post.create(:title => 'Hai')
post.comments.create(:body => 'Hi')

# This should execute 1 query on each adapter
Post.first('comments.body' => 'Hi') # => nil

# >>  ~ (0.000042) SELECT sqlite_version(*)
# >>  ~ (0.000055) DROP TABLE IF EXISTS "posts"
# >>  ~ (0.000015) DROP TABLE IF EXISTS "comments"
# >>  ~ (0.000010) PRAGMA table_info("posts")
# >>  ~ (0.000270) CREATE TABLE "posts" ("id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, "title" VARCHAR(50))
# >>  ~ (0.000007) PRAGMA table_info("comments")
# >>  ~ (0.000101) CREATE TABLE "comments" ("id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, "body" TEXT, "post_id" INTEGER NOT NULL)
# >>  ~ (0.000090) CREATE INDEX "index_comments_post" ON "comments" ("post_id")
# >>  ~ (0.000040) INSERT INTO "posts" ("title") VALUES ('Hai')
# >>  ~ (0.000076) SELECT "posts"."id", "posts"."title" FROM "posts" INNER JOIN "comments" ON "posts"."id" = "comments"."post_id" WHERE "comments"."body" = 'Hi' GROUP BY "posts"."id", "posts"."title" ORDER BY "posts"."id" LIMIT 1