Large Objects may not be used in auto-commit mode

If you can, create a intermediate Entity between MyClass and file property for instance. Something like:

@Entity
@Table(name="myobjects")
public class MyClass {
    @OneToOne(cascade = ALL, fetch = LAZY)
    private File file;
}

@Entity
@Table(name="file")
public class File {
     @Lob
     byte[] file;
}

You can't use @Lob and fetch type Lazy. It doesnt work. You must have a a intermediate class.

Instead of using @Transactional, all I did for this issue was to update this column in PostgreSQL DB from oid type to bytea type and added @Type for the @Lob field.

i.e.

ALTER TABLE person DROP COLUMN image;
ALTER TABLE person ADD COLUMN image bytea;

And changed

@Lob
private byte[] image;

To

@Lob
@Type(type = "org.hibernate.type.ImageType")
private byte[] image;

A large object can be stored in several records, that's why you have to use a transaction. All records are correct or nothing at all.

https://www.postgresql.org/docs/current/static/largeobjects.html