Union, Intersect, and Difference set operations for ActiveRecord (also, SQL's UnionAll). Has only been tested with Rails 5.
class Student < ActiveRecord::Base; end
class Employee < ActiveRecord::Base; end
(Student.select(:name, :birth_date) | Employee.select(:name, :birth_date)).where("name like John%")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.
Add this line to your application's Gemfile:
gem 'activerecord-setops'And then execute:
$ bundle
Or install it yourself as:
$ gem install activerecord-setops
If you'd like the functionality, but would prefer to avoid yet another dependency, please fill free to paste the following code into your nearest lib directory, I'm certain it's not perfect but it has been tested with Rails 5, and is being used in production.
module ActiveRecord
class Relation
def union(other)
binary_operation(Arel::Nodes::Union, other)
end
alias | union
def union_all(other)
binary_operation(Arel::Nodes::UnionAll, other)
end
alias + union_all
def intersect(other)
binary_operation(Arel::Nodes::Intersect, other)
end
alias & intersect
def difference(other)
binary_operation(Arel::Nodes::Except, other)
end
alias - difference
private
def binary_operation(op_class, other)
@klass.unscoped.from(Arel::Nodes::TableAlias.new(op_class.new(self.arel.ast, other.arel.ast), @klass.arel_table.name))
end
end
end