Migrating from other plugins with a column named differently than 'parent_id'

That's the case with me, and I had to write a migration file to rename my column to <code>parent_id</code>. Since some gems offer an option to specify the name of a parent column, it's not always named as such. I think it's helpful if <code>build_ancestry_from_parent_ids!</code> can take options to handle cases like that.