javax.persistence.PersistenceException: org.hibernate.type.SerializationException: could not deserialize

The problem was that a referenced entity had another reference to an entity and the relationship was NOT annotated by any of the @OneToMany-like annotations.

This exception may occur when hibernate obtains data of unexpected type from database query result. For example hibernate expects number but gets string instead.

In such case look for StreamCorruptedException: "invalid stream header": 74657374 exception in stacktrace. The number is hint for you, but you may want to convert it to text with ascii table. 74657374 gives test as string. Which was value of similarly named table column, but with completely different type. So hibernate was querying wrong column which happened to exist just by chance, so the first exception raised was not column does not exist but could not deserialize instead. Hibernate was expecting long but got String instead.

I got in this mess because correct @Column(name="id_user") was ignored and hibernate infered wrong column name user from field name which wasn't idUser but just user with getUser() getter. The annotation was ignored because it was specified on property getter instead of the field, which was expected by hibernate because the entity superclass annotated ID field with @Id, instead of the ID getter, which is what I groundlessly expected.

In my case it was a problem with java.time.LocalDate from Java 8, and I forgot to assign a converter to that specific attribute.

It seems that the newer Versions (5.2.1Final) has a built in converter, so that can help if your are not bound to a specific version.

But checking the Annotations is definitely the way to go, but I would check them all.