bulk update of records in rails with UPDATE SET FROM (VALUES ...) AS WHERE

rails_bulk_update.rb

    # NOTE assumes the relation is very very simple
    def bulk_update(relation, values, where_columns, set_columns)
      return if values.empty?

      connection = relation.connection
      base_class = relation.base_class

      if relation.arel.where_sql.present?
        relation_ids = relation.ids
      end

      quote_column_name_fn = connection.method(:quote_column_name)
      quote_column_value_fn = ->(value, col_name) { base_class.quote_value(value, base_class.column_for_attribute(col_name)) }

      destination_table_name_quoted = relation.quoted_table_name
      temporary_table_name_quoted = quote_column_name_fn.('tmp_data')

      temporary_table_columns = [*where_columns, *set_columns]
      temporary_table_def = "#{temporary_table_name_quoted}(#{temporary_table_columns.map(&quote_column_name_fn).join(', ')})"
      temporary_table_values_list = values.map do |record|
        record.to_h.values_at(*temporary_table_columns).map.with_index do |val, i|
          # cast is to make sure temporary table is correctly typed (e.g. timestamp without explicit type coercion is text)
          "CAST(#{quote_column_value_fn.(val, temporary_table_columns[i])} AS #{base_class.column_for_attribute(temporary_table_columns[i]).sql_type})"
        end
      end

      set_column_names_quoted = set_columns.map(&quote_column_name_fn)
      set_fields = set_column_names_quoted.map { |col| "#{col} = #{temporary_table_name_quoted}.#{col}" }.join(', ')

      where_column_names_quoted = where_columns.map(&quote_column_name_fn)
      where_cond = where_column_names_quoted.map { |col| "#{destination_table_name_quoted}.#{col} = #{temporary_table_name_quoted}.#{col}" }.join(' AND ')

      if relation_ids
        relation_cond = "#{destination_table_name_quoted}.#{quote_column_name_fn.(relation.primary_key)} IN (#{relation_ids.map {|val| quote_column_value_fn.(val, relation.primary_key) }.join(', ')})"
      end

      connection.update(<<-SQL)
        UPDATE #{destination_table_name_quoted}
         SET #{set_fields}
         FROM
          (VALUES
            #{temporary_table_values_list.map { |vals| "(#{vals.join(', ')})" }.join(', ')}
          ) AS #{temporary_table_def}
         WHERE
          #{[where_cond, relation_cond].compact.join(' AND ')}
      SQL
    end

maybe this http://stackoverflow.com/a/19033152/4212945