Postgres hstore query returning multiple values in Rails

Question

I am working with Ruby on Rails with these gems:

gem "pg",                           "~> 0.15.1"
gem "postgres_ext",                 "~> 0.3.0"
gem "activerecord-postgres-hstore", "~> 0.7.6" 

An Active Record solution would be preferable, but a strictly sql answer would work.

I have a carts table with items hstore column. An example entry in this column is:

{"1614"=>{:quantity=>"100"}, "1938"=>{:quantity=>"50"}, "1614"=>{:quantity=>"50"}, "1983"=>{:quantity=>"100"}, "1322"=>{:quantity=>"10"}, "1691"=>{:quantity=>"25"}, "1734"=>{:quantity=>"20"}}

You will notice that there is one duplicate id (1614) in the hash, but its quantity is different.

I want to write a query that will return a table with the item id counts and the total quantity. It should look like this:

 item_id | count | total 
---------+-------+------
   1614  |   2   |  150
   1938  |   1   |  50
   1983  |   1   |  50
   1322  |   1   |  100

Here is the query that I am working with:

SELECT  
skeys(carts.items) as item_ids,
COUNT(*) AS count,
svals(carts.items) as items
FROM carts
GROUP BY
skeys(carts.items),
svals(carts.items)

It returns:

 item_id | count | total 
---------+-------+------
   1614  |   2   |  {:quantity=>"150"}
   1938  |   1   |  {:quantity=>"50"}
   1983  |   1   |  {:quantity=>"50"}
   1322  |   1   |  {:quantity=>"100"}