Can't get ManyToMany to work, receive internal NPE

[Tuxgamer 32]

Hi Rob,

I got two entity classes, users and tenants. There are three database tables (two with the same name), plus users_tenants, which has user_id and tenant_id. Both columns are foreign keys to the respective tables primary keys.

From how I understood, in both entities, I will need to add a List to the other one, along with @ManyToMany annotations. One side also requires @JoinTable.

However, I am receiving a NullPointerException deep from within io.ebeaninternal. Please find the example repository here:

https://github.com/TuxGamer/ebean-example.

Important bits:

Error message: https://github.com/TuxGamer/ebean-example/blob/main/error-mesage.txt
Entity A: https://github.com/TuxGamer/ebean-example/blob/main/src/main/java/org/example/ebean/entities/UserEntity.java

Entity B: https://github.com/TuxGamer/ebean-example/blob/main/src/main/java/org/example/ebean/entities/TenantEntity.java

I am running on Java temurin-21.0.2 with a PostgreSQL database and HikariCP connection pool. All other relationships in this project work perfectly fine (OneToMany, ManyToOne).

What am I doing wrong? The documentation page for ManyToMany unfortunately shows up empty for me, so I've been operating off of random internet posts.

Thank you very much in advance,

Georg / Tux

[Rob Bygrave]

The problem here is that the UserEntity does not have a @Id property. If we add a @Id to https://github.com/TuxGamer/ebean-example/blob/main/src/main/java/org/example/ebean/entities/UserEntity.java#L15 it will work.

Ebean technically allows us to model entities without an @Id property, but in this case it is not detecting that this isn't valid for this case with the ManyToMany and is giving us an unhelpful error.

Cheers, Rob.  

[Tuxgamer 32]

Thank you so much - not sure how I missed this. It works perfectly now :D