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# ActiveRecord::Setops

Union, Intersect, and Difference set operations for ActiveRecord (also, SQL's UnionAll).
Has only been tested with Rails 5.

# Synopsis

```ruby
class Student < ActiveRecord::Base; end
class Employee < ActiveRecord::Base; end

(Student.select(:name, :birth_date) | Employee.select(:name, :birth_date)).where("name like John%")
```

# Why?

Joins can be difficult to reason about in Arel (and SQL for that matter). Many joins can be replaced
with set operations which are much simpler beasts, may offer performance gains, and have consistent
mathematical properties. But these operations while present in Arel are missing in ActiveRecord. This
module attempts to correct this lack.

# Installation

Add this line to your application's Gemfile:

```ruby
gem 'activerecord-setops'
```

And then execute:

    $ bundle

Or install it yourself as:

    $ gem install activerecord-setops

# See Also

- [Sequel](http://sequel.jeremyevans.net)
- [SQL Set Operations](https://en.wikipedia.org/wiki/Set_operations_(SQL))
- [active_record_union](https://github.com/brianhempel/active_record_union)