eugenevlasov / ctes_in_my_pg

ActiveRecord support for CTEs, cuz the postgres_ext gem doesn't support Rails 5 yet

CtesInMyPg

postgres_ext, a great gem, does not support Rails 5 yet.

Since I only ever use CTEs from that gem, I thought I'd rip out the code for that and put it in a separate gem to get CTEs working with Rails & ActiveRecord 5.

All credit goes to Dan McClain and the postgres_ext contributors ... I just stole the code ... though I did remove alias_method_chain!

It works with Rails 5 & 5.1 for sure. If you want guaranteed CTE support below that, use the postgres_ext gem.

Rails 5.2 support is on the rails-5-2-0 branch. ActiveRecord::Relation#build_arel's arity changed in Rails 5.2.0, breaking this gem.

If you're using Rails 5.2, please install via:

gem 'ctes_in_my_pg', github: 'kmurph73/ctes_in_my_pg', branch: 'rails-5-2-0'

Common Table Expressions (CTEs)

ctes_in_my_pg adds CTE expression support to ActiveRecord via:

• Relation#with

with

We can add CTEs to queries by chaining #with off a relation. Relation#with accepts a hash, and will convert Relations to the proper SQL in the CTE.

Let's expand a #with call to its resulting SQL code:

Score.with(my_games: Game.where(id: 1)).joins('JOIN my_games ON scores.game_id = my_games.id')

The following will be generated when that relation is evaluated:

WITH my_games AS (
SELECT games.*
FROM games
WHERE games.id = 1
)
SELECT *
FROM scores
JOIN my_games
ON scores.games_id = my_games.id

You can also do a recursive with:

Graph.with.recursive(search_graph:
  "  SELECT g.id, g.link, g.data, 1 AS depth
     FROM graph g
   UNION ALL
     SELECT g.id, g.link, g.data, sg.depth + 1
     FROM graph g, search_graph sg
     WHERE g.id = sg.link").from(:search_graph)

• Model.from_cte

no Model.from_cte

no support for postgre_ext's from_cte because I couldn't get it working and I don't really see the point of it anyway

PRs for from_cte support are of course welcome however

Installation

Add this line to your application's Gemfile:

gem 'ctes_in_my_pg', github: 'kmurph73/ctes_in_my_pg'

For Rails 5.2+:

gem 'ctes_in_my_pg', github: 'kmurph73/ctes_in_my_pg', branch: 'rails-5-2-0'

And then execute:

$ bundle

Or install it yourself as:

$ gem install ctes_in_my_pg

Development

After checking out the repo, run bin/setup to install dependencies.

To run the tests, create a PG db then put DATABASE_URL="postgres://[YOUR_USERNAME]:@localhost/somedb" in .env. Then run bundle exec rake db:migrate.

Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

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/kmurph73/ctes_in_my_pg.

License

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