Optimize Tree.hash_tree

[rewritten]

Right now it just executes the :hash_tree method for each root. So it's potentially a O(N) query. It can be done in one swipe, preloading by generation including the roots:

scope = Category.select("categories.*, category_hierarchies.*").
     joins("left join category_hierarchies on ancestor_id = categories.id").
     order("parent_id IS NOT NULL, generations ASC, name")

[mceachen]

You're correct, the class #hash_tree method does do 1 select for every root, but your scope won't work, as it hides the root nodes, nor does it respect the :limit_depth option.

I'll see what I can do.

[mceachen]

v3.6.3 uses 1 query now.

[rewritten]

You are right it does not take into account the :limit_depth option, but the roots are loaded first because of the left join and the parent_id is not null first order key (so roots are listed first). In any case it was just a hint, I didn't mean to provide a comlpete solution... Thanks for citing me in the changelog.