Rails AssociationTypeMismatch error I can't figure out

I'm pretty new to rails (and ruby) and I've run into what seems to be a simple problem but I've been unable to figure out what I'm doing wrong. In the code samples below I've setup Project, Attribute and User models and their associations. Additionally I've included the migration code in case my problem is there.

Seems simple enough, but when I do the following in the rails console:

proj = Project.create(:name => 'first project', :link => 'http://www.me.com', :ownerid => 1, :desc => 'First project description', :active => true)

I get this error:

ActiveRecord::AssociationTypeMismatch: Attribute(#2162685940) expected, got Array(#2151973780)

So what is it that I'm doing wrong? I get that rails is thinking it should be getting an Attribute but is instead getting an Array, but I don't understand why. I can successfully create an Attribute or a User, and when I remove the 'has_many :attributes' from the Project model I can successfully create a Project.

class Project < ActiveRecord::Base
  has_many :users
  has_many :attributes
end

class Attribute < ActiveRecord::Base
  belongs_to :project
end

class User < ActiveRecord::Base
  has_and_belongs_to_many :project开发者_开发百科
end

class CreateProjects < ActiveRecord::Migration
  def self.up
    create_table :projects do |t|
      t.string  :name
      t.string  :link
      t.integer :owner  #user_id#
      t.text    :desc
      t.boolean :active
      t.timestamps
    end
  end

  def self.down
    drop_table :projects
  end
end

class CreateAttributes < ActiveRecord::Migration
  def self.up
    create_table :attributes do |t|
      t.string  :name
      t.integer :project_id
      t.timestamps
    end
  end

  def self.down
    drop_table :attributes
  end
end

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string  :email
      t.string  :password
      t.boolean :active
      t.boolean :admin
      t.string  :location
      t.string  :phone
      t.timestamps
    end
  end

  def self.down
    drop_table :users
  end
end

Attribute is reserved word, so you should rename your model. Actually what is reserved is attributes= method. So when you are creating association has_many :attributes you are rewriting standart method

Here is API: attributes= and attributes