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This coding exercise comes from Upcase, the online learning platform we run. It's part of the Advanced ActiveRecord Querying course and is just one small sample of all the great material available on Upcase, so be sure to visit and check out the rest.

In this exercise, you'll learn how to use aggregate functions to run calculations like finding the maximum value in a data set.

To start, you'll want to clone and run the setup script for the repo

git clone [email protected]:thoughtbot-upcase-exercises/aggregations.git
cd aggregations
bin/setup

After cloning and running bin/setup:

• Review db/schema.rb to get a sense of the database schema you'll be querying.
• Take a look at the classes in app/models to get familiar with the models and associations you'll be working with.
• Edit spec/models/person_spec.rb and remove the pending line from the first spec.
• Edit app/models/person.rb and implement maximum_salary_by_location to get the spec passing.
• Edit spec/models/person_spec.rb and remove the other pending line.
• Edit app/models/person.rb again and implement managers_by_salary_difference to make the spec pass.

You can run rake to re-run the tests at any time.

Once all the tests are passing (and there are no pending specs), you're all set!

Watch the trail video on using custom joins and check out the documentation for the Calculations module.

Check out the featured solution branch to see the approach we recommend for this exercise.

If you find yourself stuck, be sure to check out the associated Upcase Forum discussion for this exercise to see what other folks have said.

When you've finished the exercise, head on back to the Advanced ActiveRecord Querying course to find the next exercise, or explore any of the other great content on Upcase.

aggregations is Copyright © 2015-2018 thoughtbot, inc. It is free software, and may be redistributed under the terms specified in the LICENSE file.

This exercise is maintained and funded by thoughtbot, inc.

The names and logos for Upcase and thoughtbot are registered trademarks of thoughtbot, inc.