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

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Delon Newman

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Feb 3, 2020, 10:39:47 PM2/3/20
to Ruby on Rails: 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
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