Newbie - Rails View Calculation - onchange?

Question

Hi all,

I am quite new to Ruby on Rails and what to make sure I set of on the right foot. I want to do some simple "Live Calculations" and am not sure of the best method. If we use the cookbook example.

Each Recipe has many ingredients. Each ingredient has a description, qty, cost and a total.

What I want to do is the following; 1) ingredient.total = ingredient.qty x ingredient.cost 2) recipe.grand_total = ingredients.sum(total)

Each time the user changes the values in ingredient.qty or ingredient.cost I want to update the totals.

What i don't know is how or where to do this :(

Any help would be great :)

Thanks in Advance, Neil

Answer 1

I think you would need to do this using javascript by using either onChange or perhaps observe_field on the two fields mentioned above.

When one of them is updated then the javascript will call your bit of code that will carry out the calculation.

Answer 2

Have been messing around and so far have come up with this explanation pulled together from various places so thought I would share.

<tr class="recipe_item">
  <td><%= f.text_field :ingredient %></td>
  <td><%= f.text_field :quantity, :class => "quantity", :onblur => "this.up('.recipe_item').down('.total').value = (parseInt(this.value) * parseInt(this.up('.recipe_item').down('.cost').value)) ;" %></td>
  <td><%= f.text_field :cost, :class => "cost", :onblur => "this.up('.recipe_item').down('.total').value =  parseInt(this.up('.recipe_item').down('.quantity').value) * (parseInt(this.value)) ;" %></td>
  <td><%= f.text_field :total, :class => "total", :readonly => true %></td>
</tr>

Not sure how efficient this is but it seems to work for the first step at least. Next thing is to find a way to summ all the recipe items to a grand total. Anyone got any comments or ideas? Thanks Neil