Enable multiple mapped variables

Context:

Configuring JPA persistence for process variables

http://mswiderski.blogspot.com/2014/02/jbpm-6-store-your-process-variables.html

https://karinavarela.me/2018/12/22/persisting-custom-process-variables-in-different-db-on-jbpm/

Implementation example:

https://github.com/jbossdemocentral/rhpam7-order-management-demo-repo

Issue:

If you try to bind more than one process variable to a process or if you deploy two projects requiring a JPA persistence you get at runtime a foreign constraint violation error. E.g.

Caused by: org.h2.jdbc.JdbcSQLException: Referential integrity constraint violation: "FK97CT3G3OQBWV7W3FQR12KHWA4: PUBLIC.MAPPEDVARIABLE FOREIGN KEY(MAP_VAR_ID) REFERENCES PUBLIC.TRAVEL(ID) (1)"; SQL statement:
update MappedVariable set MAP_VAR_ID=? where mappedVarId=? [23506-193]

Reason:

The JPA implementation of org.drools.persistence.jpa.marshaller.VariableEntity create a foreign constraints on the table MAPPEDVARIABLE due the one to many relationship 
mappedVariables.
Solution:

Add an annotation to avoid the foreign key constraint:

@JoinColumn(name = "MAP_VAR_ID", nullable = true, foreignKey = @ForeignKey(value = ConstraintMode.NO_CONSTRAINT))