(Object doesn't support #inspect)

问题:

I have a simple case, involving two model classes:

class Game < ActiveRecord::Base
  has_many :snapshots

  def initialize(params={})
   # ...
  end
end

class Snapshot < ActiveRecord::Base
  belongs_to :game

  def initialize(params={})
  # ...
  end
end

with these migrations:

class CreateGames < ActiveRecord::Migration
  def change
    create_table :games do |t|
      t.string :name
      t.string :difficulty
      t.string :status

      t.timestamps
    end
  end
end

class CreateSnapshots < ActiveRecord::Migration
  def change
    create_table :snapshots do |t|
      t.integer :game_id
      t.integer :branch_mark
      t.string  :previous_state
      t.integer :new_row
      t.integer :new_column
      t.integer :new_value

      t.timestamps
    end
  end
end

If I attempt to create a Snapshot instance in rails console, using

Snapshot.new

I get

(Object doesn't support #inspect)

Now for the good part. If I comment out the initialize method in snapshot.rb, then Snapshot.new works. Why is this happening?
BTW I am using Rails 3.1, and Ruby 1.9.2

回答1:

This is happening because you override the initialize method of your base class (ActiveRecord::Base). Instance variables defined in your base class will not get initialized and #inspect will fail.

To fix this problem you need to call super in your sub class:

class Game < ActiveRecord::Base
  has_many :snapshots

  def initialize(params={})
   super(params)
   # ...
  end
end

回答2:

I had this symptom when I had a serialize in a model like this;

serialize :column1, :column2

Needs to be like;

serialize :column1
serialize :column2

回答3:

I'm not sure exactly why, but I got this error when I accidentally misspelled 'belongs_to' as 'belong_to' in the associated class definition.