Rails - Sep 2013 - Idea to manipulate the ActiveRecord Relation

Hi, 
in my project I needed to manage a set of query that fondamentally was a 
great sql union.
I had a cycle that was running a query, and the resultant recordset was 
added to a variable with the += method. After some attempts I setted this 
var as Array because
I found that the sum of ActiveRecord::Relation gave me an Array of objects! 

But this was only half the job: I needed to work on that Array with 
aggregation function as sum and found nothing to help me than write my own 
code.

So the idea!

The sum of ActiveRecord::Relation objects returns a special Union object?
This object act as a memory table and expose methods like select, ,find, 
group, sum, average and all the other valid for AR::Model object, 
the difference is that the fields of this "table" will be created at 
runtime, based on the first AR::Relation object passed to 
and all the other AR::Relation added need to have the same structure.

In this manner i wiil be easy to do
 
   @recs = Union.new
   Model1.each do |m1|
       @recs += Model2.select...where....(:att1=>m1.attr)  #what will be 
necessary
   end

   @recs.select(''f1 as myfield, sum(f2) as total, average(f3) as 
avv'').group(:id_field)    


I propose this class because I am not able to achieve.

Thanks for read
Giorgio

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