For JPA 2.0 (OpenJPA trunk), the map key does not need to be a field in the
target entity. For example, please see the test case in
org.apache.openjpa.persistence.jdbc.maps.*.
----- Original Message ----
From: "KARR, DAVID (ATTCINW)" <dk0...@att.com>
To: users@openjpa.apache.org
Sent: Tue, December 29, 2009 9:36:53 AM
Subject: How to implement a map where the key is in the join table, not in the
target table?
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.
