Why Active Record storing integer value in the format of BigDecimal notation?

I am a newbie. observe following screen shots, I have a model Books with following columns.

class CreateBooks < ActiveRecord::Migration
  def change
   create_table :books do |t|
     t.string :title
     t.text :author
     t.integer :price
     t.integer :book_id
    end
 end
end

Later i add a coulumn to existing table like following

class AddBookIdToBooks < ActiveRecord::Migration
  def change
    add_column :books, :book_id, :integer
  end
end

i add a record into table Book using form helpers. but it is storing book_id value in the format of BigDecimal notation insted of integer. why it is storing like that?? Thanks in Advance.

observe following screen shot here

2.2.2 :023 > Book.all
Book Load (0.4ms)  SELECT "books".* FROM "books"
=> #<ActiveRecord::Relation [#<Book id: 7, title: "Wings Of Fire",   author: "kalam's", price: 120, created_at: "2015-12-09 09:57:10", updated_at: "2015-12-09 09:57:10", book_id: #<BigDecimal:4f39ea0,'0.1001E4',9(27)>>]>