Finds in Rails 3 and ActiveRelation - ruby-on-rails

Question

I'm trying to understand the new arel engine in Rails 3 and I've got a question.
I've got two models, User and Task
class User < ActiveRecord::Base
has_many :tasks
end
class Task < ActiveRecord::Base
belongs_to :user
end
here is my routes to imply the relation:
resources :users do
resources :tasks
end
and here is my Tasks controller:
class TasksController < ApplicationController
before_filter :load_user
def new
#task = #user.tasks.new
end
private
def load_user
#user = User.where(:id => params[:user_id])
end
end
Problem is, I get the following error when I try to invoke the new action:
NoMethodError: undefined method `tasks' for #<ActiveRecord::Relation:0x3dc2488>
I am sure my problem is with the new arel engine, does anybody understand what I'm doing wrong?
Sorry guys, here is my schema.db file:
ActiveRecord::Schema.define(:version => 20100525021007) do
create_table "tasks", :force => true do |t|
t.string "name"
t.integer "estimated_time"
t.datetime "created_at"
t.datetime "updated_at"
t.integer "user_id"
end
create_table "users", :force => true do |t|
t.string "email", :default => "", :null => false
t.string "encrypted_password", :limit => 128, :default => "", :null => false
t.string "password_salt", :default => "", :null => false
t.string "reset_password_token"
t.string "remember_token"
t.datetime "remember_created_at"
t.integer "sign_in_count", :default => 0
t.datetime "current_sign_in_at"
t.datetime "last_sign_in_at"
t.string "current_sign_in_ip"
t.string "last_sign_in_ip"
t.datetime "created_at"
t.datetime "updated_at"
t.string "username"
end
add_index "users", ["email"], :name => "index_users_on_email", :unique => true
add_index "users", ["reset_password_token"], :name => "index_users_on_reset_password_token", :unique => true
add_index "users", ["username"], :name => "index_users_on_username", :unique => true
end

Answer 1

I believe you want:
def load_user
#user = User.where(:id => params[:user_id]).first
end
Until you ask for a record it will stay a relation.
But find(params[:user_id]) will still work and return the record.

Answer 2

Does it work if you change your load_user method as shown below?
def load_user
#user = User.find(params[:user_id])
end
Also, I think you might need to change your new action to:
def new
#task = #user.tasks.build
end

Answer 3

Don't confuse the Arel gem's interface with the new ActiveRecord query interface. The syntax described here will not work: http://github.com/brynary/arel
ActiveRecord uses Arel under the hood but creates its own Arel-like API. Here's a brief look at the new ActiveRecord query interface: http://m.onkey.org/2010/1/22/active-record-query-interface

Answer 4

It's actually pretty simple. Here is one method...
def new
#task = #user.tasks.new
end
private
def load_user
# you must call a non-deferred operator to actually return
# the tuple that is connected to your tasks
#user = User.where(:id => params[:user_id]).first
end
Be sure to take a look at the seven part learning series I am doing on Active Relation. The first episode will help you understand what your error was more clearly. http://Innovative-Studios.com/#pilot
find() IS NOT deprecated in some instances as stated before. I would limit the use of find() for atomic values (where you are searching for a specific item/index) Anything that could possibly be collection based I would stick to the Where (restriction) clause wrapper in ActiveRecord for Arel.