arel-fun.rb

#!/usr/bin/env ruby

identifying_attrs = {
  updateable_type: 'Contact',
  updateable_id: 123,
  external_source_id: 123,
  attribute_name: 'title'
}

non_identifying_attrs = {
  attribute_value: 'Grand PooBah'
}

def to_bind_params(attrs, table)
  attrs.to_a.map do |pair|
    [table[pair.first], pair.last]
  end
end

entity_changes = Arel::Table.new(:entity_changes, ActiveRecord::Base)

insert_manager = Arel::InsertManager.new(ActiveRecord::Base)
insert_manager.insert(to_bind_params(identifying_attrs.merge(non_identifying_attrs), entity_changes))

update_manager = Arel::UpdateManager.new(ActiveRecord::Base)

where_clause = identifying_attrs.to_a.map do |pair|
  entity_changes[pair.first.to_s].eq(pair.last)
end
update_manager.table(entity_changes).where(entity_changes.create_and(where_clause))

update_manager.set(to_bind_params(non_identifying_attrs, entity_changes))

sql = insert_manager.to_sql
conflict_keys = identifying_attrs.keys.map { |k| k.to_s }.join(', ')
sql << "\nON CONFLICT (#{conflict_keys}) DO\n"
sql << update_manager.to_sql.sub(/^UPDATE "#{entity_changes.name}"/, "UPDATE")

puts sql