在Rails中将总和添加到表中的正确方法是什么？

Question

I'm displaying a list of items which have a price attribute in an HTML table.

What is the right way of getting the total price add the end of the table (and where should the calculation happen)?

I can think of 3 obvious ways, but I don't know which one is the most "orthodoxic"

1- in the controller

@items = Item.all
@item_total = @items.sum(:price)

and I simply display @item_total in my last line

2- in the view, on the last line

<%= @items.sum(:price) %>

But I'm not sure that it's OK to do this in a view (it works, but is it OK?)

3- in the view, add this on the last line

<%= @items.inject(0){|s, e| s + e.price} %>

But this doesn't feel right to add this kind of logic in the view.

So which one of these is the right one? Or is there another way I'm missing?

Answer 1

You should use first option, as view should contain least code. Hence use your code in controller only.

Answer 2

@items = Item.all
# this is Array#sum, calculation is done in Ruby. usually slow
@items.sum(:price) 

whereas

# this is Relation#sum -> does a calculation at DB. usually faster
Item.scoped.sum(:price) # OR Item.sum(:price)

Answer 3

It is always desirable to reduce the number of queries that are required to fetch the data from the DB.... You have two options to fetch your data...

@items = Item.all @item_total = @items.sum(:price)

This would not run as there should be &:price instead of :price...more over if this style of code is now being discouraged due to the non support for the ARel...

Therefore, according to me the code that you should use

@items = Item.scoped @item_total = @items.pluck(:price).sum(:price)

The benefit is that the @item is an ARel object and can be used in the further calculations...

Answer 4

try this way

# In your controller write
@item_total = Item.sum(:price)

and @item_total use in your view file

Update

If you use this like index action then you can do this way

@items = Item.all
@item_total = @items.sum(:price)

but if you want to only item_total then don't pass two queries for sum you can do like

@item_total = Item.sum(:price)

Answer 5

您可以尝试以下代码：

Sum Dolars: <%= @customer_reports.sum(&:mount) %>