bulk_insert.rb

# Takes a table name, and an array of hashes where keys are column names and values are values.
# Expects hashes to all contain the same keys.
def bulk_insert(table, rows)
  columns = rows.first.keys

  to_insert = rows.map do |d|
    vals = columns.map {|k| d[k] }
    ActiveRecord::Base.send(:replace_bind_variables, "(#{vals.length.times.collect {'?'}.join(',')})", vals)
  end

  ActiveRecord::Base.connection.execute(<<-SQL)
    INSERT INTO
      #{table}
    (#{columns.join(',')})
    VALUES #{to_insert.join(",")}
  SQL
end

bulk_update.rb

SQL = <<-SQL 
    update test as t set
    column_a = c.column_a,
    column_c = c.column_c
    from (values
           ('123', 1, '---'),
           ('345', 2, '+++')  
         ) as c(column_b, column_a, column_c) 
    where c.column_b = t.column_b;
    SQL

Book.connection.execute(SQL)