Posts Tagged ‘Public Cloud’

Managing Multiple Parent Persistence Problem in App Engine

August 7, 2010 3 comments

We are in process of porting an entire application on google app engine. This application has persistence using JPA and as usual contains mapping between entities using annotations. The mapping like @OnetoMany and @ManytoOne in Jpa may throw lot of errors in google app engine and therefore is neither straightforward nor trivial. In this blog we will see where our mapping may fail, with specific problem related to multiple parent key provider fields. Google app engine may throw this error in our application, we will see how can we manage it with unowned relationships in our application.

We have three entities User, Project and ProjectAssignment. ProjectAssignment entity has @ManyToOne mapping with an User and a Project. In these relationships we also have a bidirectional mapping using @OneToMany relationship from User and Project for ProjectAssignment.
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