mongodb get count of orders in each zip code - ruby-on-rails

Question

Hi we are using rails with mongo and we have a collection called orders which contain a specific zip code for each customer. We want to retrieve a count of how many orders belong to each zip code and what time frame they appear in most.
The docs can have basic information such as :
{"zip" : 60010,
"order_time" : <whatever the time for the order is>
}
Right now i have an aggregation using ruby:
coll_orders.aggregate([{"$group" => {"_id" => "$zip", "numOrders" => {"$sum" => 1}}}, {"$sort" => {"numOrders" => 1}}])
and it results with:
{"_id" : 60010,
"numOrders" : 55
}
My question is how do i add functionality in the aggregation so that i can get additional fields where it shows a breakdown of when the orders usually happen? Essentially a result document like :
{"_id" : 60010,
"numOrders" : 55,
"morning" : 25,
"afternoon" : 10,
"evening" : 20
}
edit: spelling/missed quotes

Answer 1

The best way to approach this would be calculate and store the minutes separately using a $project phase and use that to group by. I have provided a sample query below that'll run in the shell for just calculating the orders placed in the morning. You can extend this for the results you are expecting.
db.foo.aggregate( [
{ $project: {
zip: 1,
order_time: 1,
minutes: { $add: [
{ $multiply: [ { $hour: '$order_time' }, 60 ] },
{ $minute: '$order_time' }
] }
} },
{ $group: {
_id:"$zip",
numOrders:{$sum:1}
morning:{$sum:{$cond:[{$lt:["$minutes",12*60]}, 1, 0]}}}}
] );

Answer 2

You can use the following mongoid queries to fetch the data you need:
Count in each zip code:
Order.where(:zip => zip).count
And for count in a given time slot (you will need to create separate queries for each time slot - morning, afternoon, etc.):
Order.where(:zip => zip, :order_time => {'$gt' => start_time, '$lt' => end_time}).count
You can either keep inserting each unique zipcode in a separate collection to get a list of all zip codes, or if you don't run this task often (and your collection is small), you can get a list of all the unique zip codes in your collection using:
zips = Order.all.map{|o| o.zip}.compact.uniq
and iterate over this array and do the above queries.