Hello Marius K, the error you’re seeing is triggered by a new check we introduced. The mappedBy member of @OneToMany annotation is used to define bi-directional associations between 2 entity types, with the entity which defines it being the non-owning (or inverse) side of the association. You’re using it incorrectly, it doesn’t make sense to indicate a mappedBy pointing to Integer property. Please refer to the User Guide for more information.

I think what you’re trying to do might indicating that the id.contractId property of Entity Contractposition should be used as a join column, which case you should use some like @JoinColumn(name="VERTRAG_ID").