How to map lookup main table field in another main table using MDM 7.1?

Question

We created a new SAP MDM 7.1 repository with multiple main tables.  The first main table is called ProductMaster table which contains Products information.  The ProductCode is the primary key and the only display field for the table during data loading process. The second main table is ProductByRegion table which has a main table lookup field ProductCode and a RegionId field.  These two fields (ProductCode and RegionId) combine as the PK for this main table.  Both main tables have key mapping enabled. 
I was able to load ProductMaster table using Import Manager.  But Iu2019m having trouble to load data into ProductByRegion table using MDM Import Manager.  Although I have met all the 5 requirements below (excerpted from MDM Import Manager Reference Guide P.222), the ProductCode wonu2019t show up on the destination value pane.  If I mapped all productCode to NULL field, ProductCode wonu2019t load.  If I u2018Addu2019 all ProductCode to Destination Value pane, the Import Manager added duplicated rows to Product Master table while only loading 1 record to ProductByRegion table.  I canu2019t get ProductCode show up in Matching Destination Field list.  When I checked ProductMaster records in MDM Data Manager, I right-clicked on one of records, chose Edit Key Mappings, it didnu2019t show anything.  However, if I right-clicked on one of those duplicated rows, Edit Key Mapping shows remote system and key correctly.
Where did I do wrong?  How can I fix the problem?
Thank you for help in advance.
From: SAP MDM Import Manager Reference Guide:
Mapping to Main Table Lookup Destination Fields
Import Manager handles main table lookup fields (Lookup [Main])
differently than other MDM lookup fields. Specifically, Import Manager
does not display the complete set of display field values of the records
of the underlying lookup table. Instead, the values it displays for a main
table lookup field are limited by both the key mappings for the lookup
table and the values in the source file.
Also, Import Manager does not automatically display the values of a
Lookup [Main] destination field in the Destination Values grid when you
select the field in the Destination Fields grid. Instead, for a main table
lookup field value to appear in the Destination Values grid, all of the
following conditions must be met:
u2022 The lookup table must have key mapping enabled
u2022 The lookup field must be mapped to a source field
u2022 The source field must contain key values for the lookup table
u2022 The destination value must have a key on the current remote system
u2022 The destination valueu2019s key must match a source field value
NOTE ►► The current remote system is the remote system that was
selected in Import Manageru2019s Connect to Source dialog (see
u201CConnecting to a Remote Systemu201D on page 416 for more information).
Vicky

Answer 1

Hi Michael,
Thank you very much for your response.  I'm new to SAP MDM, I need some clarification and help regarding your solution. 
I did use two maps to load ProductMaster and ProductByRegion separately.  Here were my steps:
1. create main table ProductMaster with key mapping enabled at the table level and set ProductCode as unique and writable once (primary key).
2. create a map to load ProductMaster record from a staging table located an oracle database.  But Key mapping didn't show anything when I looked at them using Data Manager.
3. create main table ProductByRegion with a lookup field looking at ProductMaster table.  This field and RegionId combines as a unique field for ProductByRegion table. 
4. create a map to load ProductByRegion table.  But ProductCode records only shows on the source pane not destination pane and can't be mapped properly.
My questions:
1. How can I "Ensure that you add key mapping info for all ProductMaster records" besides enabling Key Mapping on the table level?
2. How can I define a concatenation of ProductCode and RegionId as a REMOTE KEY"?
Thanks a lot for your help!
Vicky