The information I've read about the "map" construct is that the key value used in the map is taken from a field in the target entity. I have a situation where I need to define a map where the key value is a column in a join table, not the target table.
Here's an example of the structure I have: Table FOO: ---------- VARCHAR FOO_ID INT TYPE Table FOO_BILLING_INFO: ------------------ VARCHAR FOO_ID VARCHAR BILLING_SYSTEM VARCHAR BILLING_INFO_ID Table BILLING_INFO: ------------------- VARCHAR BILLING_INFO_ID VARCHAR BILL_CODE VARCHAR SYSTEM_NAME There is a "OneToMany" relationship from FOO to BILLING_INFO. The "key value" for the map is intended to be the "BILLING_SYSTEM" value in the join table. Also note that the values of "BILLING_SYSTEM" are not the same as or related to the values for "SYSTEM_NAME" in BILLING_INFO (that was my first guess). For each unique value of "FOO_ID" in "FOO", there will be two "FOO_BILLING_INFO" rows with different "BILLING_SYSTEM" values, and each of those two rows will point to a "BILLING_INFO" row, sometimes the same one for both "FOO_BILLING_INFO" rows, but sometimes not.
