product_id is different blob

```
[4] pry(#<ProductHistoriesController>)> params.require(:product_history)
=> {"date"=>"2014-01-10", "price"=>"1", "count"=>"1"}
[5] pry(#<ProductHistoriesController>)> params.require(:product_history).merge('product_id' => params[:product_id])
=> {"date"=>"2014-01-10", "price"=>"1", "count"=>"1", "product_id"=>"1"}
```