Elixir/Phoenix query incl quantity - psql

Question

I have following tables in my db:
schema "foods" do
field :name, :string
has_many :order_items, MyApp.OrderItem
end
schema "order_items" do
field :quantity, :integer, default: 1
field :price, :integer
belongs_to :food, MyApp.Food
Order items keeps the food_id, as well as quantity. Now I'm trying to create a query that will show how much each food item has been ordered. This is what i have so far:
fooditems = Repo.all(from p in OrderItem, join: f in Food, on: p.food_id == f.id,
group_by: f.name, select: {f.name, count(p.id)}, order_by: count(p.id))
Basically, I have two questions: 1) How can I make quantity field(from order item table) be also included in the query count? For example, if in order item the quantity is 2, the count() will only count is as only 1, so how can I make the count() to count not only by id, but also include the quantity(from order item table, quantity field)?
Additionally, I'm not sure how to call the query from the html. I've tried
<%= for item <- #fooditems do %>
<tr>
<td><%= item.name %></td>
</tr>
<% end %>
But it returns argument error, so I believe, I'm just calling it the wrong way with item.name. Generally, I want to have a table that will list food names, and the respective quantity (from order_item table, incl quantity field).
Thanks

Answer 1

As you're doing a group_by on the Food's name, I'm guessing you want the sum of quantity. Here's how I would do it:
Repo.all(from p in OrderItem,
join: f in Food,
on: p.food_id == f.id,
group_by: f.name,
select: %{name: f.name, count: count(p.id), quantity: sum(p.quantity)},
order_by: count(p.id))
This generates the following query:
SELECT f1."name", count (o0."id"), sum (o0."quantity") FROM "order_items" AS o0 INNER JOIN "foods" AS f1 ON o0."food_id" = f1."id" GROUP BY f1."name" ORDER BY count (o0."id")
For the second part, Repo.all returns a list of whatever you have in the select part of your query, which in your case was a tuple, and not a map, but you tried to access it like a Map.
For your original query, this will work:
<%= for {food_name, count} <- #fooditems do %>
For the query I wrote above, which returns a Map, you can access the fields easily:
<%= for item <- #fooditems do %>
<tr>
<td><%= item.name %></td>
<td><%= item.count %></td>
<td><%= item.quantity %></td>
</tr>
<% end %>