Row base looping to merge table base on variable keys (Nested loop)

Hi,

I have a script in pyhton that does the job but I was ask to re-write the code in M.

The problem is the folowing.

I have 1 table with transactional record (Transaction_table)

Second table containing rules that need to be validated in order (rule_table)

So if the transaction key match the mapping rule a row one insert the mapping results for row one, else move to the second rule until you find a match is no match found, well no match is the value to insert in the transaction.

Note: that the match need to be done row by row since it's priority based

the only thing is that the key for the merge is variable base on the rule (mapping table)

 In python it's 2 loop imbeded once you find the result you break the loop and return the results but in M i am not sure if this is possible or I am not really sure how to implement the solution.

thks for your help