Getting common ancestors / merging ancestors

[mbajur]

Hello!

I have a case in which i have multiple sets of self_and_ancestors results. The amount of these sets depends on the variable which makes it unpredictable and N+1 prone therefore i was looking for some ways of simplifying that with one query. Let's say my code looks as follows:

taxons = []

product.taxons.each do |taxon|
  taxon.self_and_ancestors.each { |t| taxons << t }
end

Which obviously produces new query for each self_and_ancestors call. So if there are 100 product.taxons, 100 queries will be produced.

I was experimenting with doing that with merge:

collection = Spree::Taxon.all
product.taxons.each do |taxon|
  collection.merge!(taxon.self_and_ancestors)
end

which indeed produced one single query but it operates on lft and rgt columns and i have no idea if that's proper way of handling that and/or this produced sql query is valid. In fact, it merged where statements for all of the self_and_ancestors calls.

For your convenience, i prepared an example for you. Let's say product.taxons returns two taxons. Here are the sql queries produced for each one of them:

product.taxons.first.self_and_ancestors.to_sql
# => SELECT "spree_taxons".* FROM "spree_taxons" WHERE "spree_taxons"."lft" <= 1 AND "spree_taxons"."rgt" >= 232 ORDER BY lft

product.taxons.last.self_and_ancestors.to_sql
# => SELECT "spree_taxons".* FROM "spree_taxons" WHERE "spree_taxons"."lft" <= 201 AND "spree_taxons"."rgt" >= 202 ORDER BY lft                                                                                     

And here is the result of merging them:

collection = Spree::Taxon.all
product.taxons.each do |taxon|
  collection.merge!(taxon.self_and_ancestors)
end
collection.to_sql
# => SELECT "spree_taxons".* FROM "spree_taxons" WHERE "spree_taxons"."lft" <= 201 AND "spree_taxons"."rgt" >= 202 ORDER BY lft

Does that look valid to you? Is that how i should approach that?

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