Converts from using a foreign relationship table to using a materialized path in the same table (using ancestry)

code.txt

relationships = Relationship.where(relationship: 'genealogy', resource_type: 'VmOrTemplate').select(:id, :resource_id, :ancestry).to_a
rel_by_rel_id = relationships.index_by(:id) # relationship => resource_id
rel_by_vm_id = relationships.index_by(:resource_id) # resource_id => ancestry

Vm.where(:id => Relationship.select(:resource_id)).each_in_batches do |vm|
  ancestry = rel_by_vm_id[vm.id].ancestry.split("/").map { |rel_id| rel_by_rel_id[rel_id].resource_id.to_s }.join("/")
  vm.update_attribute(:ancestry => ancestry)
end

--- step 1 ancestry for the relationships (split apart)

def ancestry_resource_ids(relationship, model_class_name, id_range)
  Relationship.where(
    :relationship => relationship,
    :resource_type => model_class_name,
    :resource_id => id_range
    ).each_with_object([]) do |a_rels, ret|

    a_rels.ancestry.split('/').map(&:to_i)
          .each_with_index do |rel_id|
      ret << [a_rels.resource_id, rel_id]
    end
  end
end

def ancestry_resource_ids(relationship, model_class_name, id_range)
  %q{
SELECT a_rels.resource_id AS src_id, relationships.id AS rel_id
FROM   relationships a_rels
LEFT JOIN LATERAL UNNEST(STRING_TO_ARRAY(a_rels.ancestry, '/')::BIGINT[])
WITH ORDINALITY AS relationships(id, indx) ON TRUE
WHERE  a_rels.relationship = '#{relationship}'
AND    a_rels.resource_type = '#{model_class_name}'
AND    a_rels.resource_id BETWEEN #{id_range.first} AND #{id_range.last}
ORDER BY a_rels.resource_id, relationships.indx
  }
end

---- step 2 new ancestry with src_id from ancestry with rel_id
def ancestry_of_src_ids_for_src(ancestry_resources, relationship)
  ancestry_resources.group_by {|src_id, rel_id| src_id }
                    .map do |src_id, recs|
      {
        src_id: src_id,
        new_ancestry: recs.map {|rec| Model.find(id: rec.rel_id).resource_id }
                          .map(&:to_s).join('/')
      }
    }
end

SELECT ancestry_resources.src_id AS src_id,
ARRAY_TO_STRING(ARRAY_AGG(res_rels.resource_id)::VARCHAR[], '/') AS new_ancestry
FROM ( #{ancestry_resources}
) AS ancestry_resources
JOIN relationships res_rels
  ON res_rels.id = ancestry_resources.rel_id
GROUP BY ancestry_resources.src_id


def update_src(model, new_ancestors)
  UPDATE vms
  SET ancestry = new_ancestry
  FROM ( #{new_ancestors}
  ) AS new_ancestors
  WHERE new_ancestors.src_id = vms.id
  SQL
end


ancestry_resources = ancestry_resource_ids()
new_ancestors = ancestry_of_src_ids_for_src(ancestry_resources, )
update_src(VmOrTemplate, new_ancestors)
----    

      UPDATE vms
      SET ancestry = new_ancestry
      FROM (
        -- join to resources to convert rel.id to vm.id (it is in resource_id column)
        -- ARRAY_AGG takes multiple rows and converts to an array
        SELECT ancestor_resources_for_vms.vm_id AS vm_id,
        ARRAY_TO_STRING(ARRAY_AGG(res_rels.resource_id)::VARCHAR[], '/') AS new_ancestry
        FROM (
          -- get vm and associated ancestor rel_id
          -- unnest converts an array to multiple rows, 1 ancestor per row
          -- with ordinality, and order by relationships.indx make sure ancestors stay in the same order
          SELECT vms.id AS vm_id, relationships.id AS rel_id
          FROM vms
          JOIN relationships a_rels ON a_rels.resource_id = vms.id
          AND a_rels.relationship = 'genealogy'
          AND a_rels.resource_type = 'VmOrTemplate'
          LEFT JOIN LATERAL UNNEST(STRING_TO_ARRAY(a_rels.ancestry, '/')::BIGINT[])
          WITH ORDINALITY AS relationships(id, indx) ON TRUE
          WHERE vms.id BETWEEN #{id_range.first} AND #{id_range.last}
          ORDER BY vms.id, relationships.indx
        ) AS ancestor_resources_for_vms
        JOIN relationships res_rels ON res_rels.id = ancestor_resources_for_vms.rel_id AND res_rels.relationship = 'genealogy'
        GROUP BY ancestor_resources_for_vms.vm_id
      ) AS new_ancestors_for_vms
      WHERE new_ancestors_for_vms.vm_id = vms.id

assumption of my concern is that all the vms in the genealogy chain are local and not hidden by the server.
I think they can be archived and the oids for archived vms still come back.

(and this would be pruned out by joining to vms) - but then our data would be different from the source (e.g. vmware) and we don't want that either.)

If I knew what to do I would be fixing the code and not writing a comment