Would it be useful to include set operations in ActiveRecord core?

Hello all,

When dealing with legacy schemas or data models where the Active Record pattern is a bit of a stretch complex joins are often necessary. Many joins can be eliminated by using set operations on multiple queries.

Arel already supports set operations, and the Set module from the standard library already provide useful semantics.

Would this be something that could be of general use?

I’ve created a gem that patches these operations into ActiveRecord::Relation (https://github.com/delonnewman/activerecord-setops), and tested it with Rails 5. It’s very little code:

module ActiveRecord
class Relation
# Performs a set theoretic union works like Array#+ but puts the load on the database
# and allows you to chain more relation operations.
def union(other)
binary_operation(Arel::Nodes::Union, other)
end
alias | union
alias + union

def union_all(other)
  binary_operation(Arel::Nodes::UnionAll, other)
end

def intersect(other)
  binary_operation(Arel::Nodes::Intersect, other)
end
alias & intersect

def except(other)
  binary_operation(Arel::Nodes::Except, other)
end
alias difference except
alias - except

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

``

Thanks,

Delon Newman