how to add set of values depending on particular order nember

Hi Expers,

I have a requirement,

for particular order no,,,there will be multiple line numbers, for each line item there will be cost. My requirement is I need to add all the line item values for each order no.

Example

Order1

line item 1 cost: 10

line item 2 cost: 20

Order2

line item 1 cost: 30

line item 2 cost: 40

I will be inserting the records to database depending on no. or order items, in this case two rows will be inserted for first order 30 to cost field, and second order 70 to cost field.

how to achieve this with message mapping? Quick response is appreciate.

Thanks,

Chandar