CalculateAll

Provides the #calculate_all method for your Active Record models, scopes and relations. It's a small addition to Active Record's #count, #maximum, #minimum, #average and #sum. It allows you to fetch all of the above, as well as other aggregate function results, in a single request, with support for grouping.

Currently tested with Postgres, MySQL and sqlite3, ruby >= 2.3, rails >= 4, groupdate >= 4.

Usage

stats = Order.group(:department_id).group(:payment_method).calculate_all(
  :count,
  :count_distinct_user_id,
  :price_max,
  :price_min,
  :price_avg,
  price_median: 'percentile_cont(0.5) within group (order by price desc)'
)
#
#   (2.2ms)  SELECT department_id, payment_method, percentile_cont(0.5) within group (order by price desc),
#      COUNT(*), COUNT(DISTINCT user_id), MAX(price), MIN(price), AVG(price) FROM "orders" GROUP BY "department_id", "payment_method"
#
# => {
#   [1, "cash"] => {
#     count: 10,
#     count_distinct_user_id: 5,
#     price_max: 500,
#     price_min: 100,
#     price_avg: 0.3e3,
#     price_median: 0.4e3
#   },
#   [1, "card"] => {
#     ...
#   }
# }

(median example works in Postgres only, but check out very cool https://github.com/ankane/active_median)

Rationale

Active Record makes it really easy to use most common database aggregate functions like COUNT(), MAX(), MIN(), AVG(), SUM(). But there's a whole world of other powerful functions in Postgres, which I can’t recommend enough, especially if you’re working with statistics or business intelligence. MySQL has some useful ones as well.

Also, in many cases, you’ll need multiple metrics at once. Typically, the database performs a full scan of the table for each metric. However, it can calculate all of them in a single scan and a single request.

#calculate_all to the rescue!

Arguments

#calculate_all accepts a list of expression aliases and/or expression mappings. It can be a single string of SQL,

  Model.calculate_all('SUM(price) / COUNT(DISTINCT user_id)')

a hash of expressions with arbitrary symbol keys

  Model.calculate_all(total: 'COUNT(*)', average_spendings: 'SUM(price) / COUNT(DISTINCT user_id)')

and/or a list of one or more symbols without expressions, in which case #calculate_all tries to guess what you wanted from it.

  Model.calculate_all(:count, :average_price, :sum_price)

It's not so smart right now, but here's a cheatsheet:

symbol	would fetch
:count	COUNT(*)
:count_column1, :column1_count	COUNT(column1) (doesn't count NULL's in that column)
:count_distinct_column1, :column1_distinct_count	COUNT(DISTINCT column1)
:max_column1, :column1_max, :maximum_column1, :column1_maximum	MAX(column1)
:min_column1, :column1_min, :minimum_column1, :column1_minimum	MIN(column1)
:avg_column1, :column1_avg, :average_column1, :column1_average	AVG(column1)
:sum_column1, :column1_sum	SUM(column1)

Please don't put values from unverified sources (like HTML form or javascript call) into expression list, it could result in malicious SQL injection.

Result

#calculate_all tries to mimic magic of Active Record's #group, #count and #pluck so result type depends on arguments and on groupings.

If you have no group() on underlying scope, #calculate_all will return just one result.

# Same as Order.distinct.count(:user_id), so probably a useless example.
# But you can use any expression with aggregate functions there.
Order.calculate_all('COUNT(DISTINCT user_id)')
# => 50

If you have a single group(), it will return a hash of results with simple keys.

# Again, Order.group(:department_id).distinct.count(:user_id) would do the same.
Order.group(:department_id).calculate_all(:count_distinct_user_id)
# => {
#   1 => 20,
#   2 => 10,
#   ...
# }

If you have two or more groupings, each result will have an array as a key.

Order.group(:department_id).group(:department_method).calculate_all(:count_distinct_user_id)
# => {
#   [1, "cash"] => 5,
#   [1, "card"] => 15,
#   [2, "cash"] => 1,
#   ...
# }

If you provide only one argument to #calculate_all, its calculated value will be returned as-is. Otherwise, the results will be returned as hash(es) with symbol keys.

so, Order.calculate_all(:count) will return just a single integer, but

Order.group(:department_id).group(:payment_method).calculate_all(:min_price, expr1: 'count(distinct user_id)')
# => {
#   [1, 'cash'] => {min_price: 100, expr1: 5},
#   [1, 'card'] => {min_price: 150, expr2: 15},
#   ...
# }

You can pass a block to calculate_all. Rows will be passed to it, and returned value will be used instead of the row in the result hash (or returned as-is if there's no grouping).

Order.group(:country_id).calculate_all(:count, :avg_price) { |count:, avg_price:|
  "#{count} orders, #{avg_price.to_i} dollars average"
}
# => {
#   1 => "5 orders, 120 dollars average",
#   2 => "10 orders, 200 dollars average"
# }

Order.group(:country_id).calculate_all(:avg_price) { |avg_price| avg_price.to_i }
# => {
#   1 => 120,
#   2 => 200
# }

Order.calculate_all(:count, :max_price, &OpenStruct.method(:new))
# => #<OpenStruct max_price=500, count=15>

groupdate compatibility

calculate-all should work with groupdate too:

Order.group_by_year(:created_at, last: 5).calculate_all(:price_min, :price_max)
# => {
#   Sun, 01 Jan 2012 => {},
#   Tue, 01 Jan 2013 => {},
#   Wed, 01 Jan 2014 => {},
#   Thu, 01 Jan 2015 => {},
#   Fri, 01 Jan 2016 => {:price_min=>100, :price_max=>500}
# }

It works even with groupdate < 4, though you'd have to explicitly provide default_value: {} for blank periods.

Installation

Add this line to your application's Gemfile:

gem 'calculate-all'

And then execute:

$ bundle

Or install it yourself as:

$ gem install calculate-all

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. Run BUNDLE_GEMFILE=gemfiles/activerecord60.gemfile bundle then BUNDLE_GEMFILE=gemfiles/activerecord60.gemfile rake to test agains specific active record version.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/codesnik/calculate-all.

License

The gem is available as open source under the terms of the MIT License.