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