Inserting new record in XDataWebDataset when entity has foreign key.

I have two tables A ( master) and B ( detail) linked by foreign key. B.ID -> A.ID ( column name is the same in both tables)
and I have two XDataWebDataset in my project . One for entity A and one for entity B.
I am using Aurelius.
can you tell me please when I add a new record to dataset B how am i supposed to set the ID field? In B dataset the ID field type is TXDataWedDataset ( table A). I was thinking aurelius will take care of the foreign key fields.

Thank you.

I think i found a solution but would like to get a confirmation that i am doing it right please.
This is an example when the foreign key contains 2 columns: C1 and C2. C1 is string. C2 is integer.
Lets say in the master record C1 = 'ABC' and C2 = 123
Is this correct to assign the data in the ONNEWRECORD event like this:

TJSObject(DETAIL_DATASET.CurrentData)['C1@xdata.ref'] := 'MASTER_TABLE(' + '''' + 'ABC' + '''' + ',123)';

( I understand that i can use some formatting functions here.)

Yes, that's correct. That's how you use composite keys with XData, values separated by comma.

Thank you.