休眠：org.hibernate.PropertyAccessException：IllegalArgumentException

Question

I have a parent table (MHS_USER) and associated child table (GROUP) mapped with ManyToMany relation as follows (the relevant code below)

@Entity
@Table(name = "mhs_user")
public class MHSUser extends implements Comparable<User> {
        @ManyToMany(fetch = FetchType.EAGER, cascade = { CascadeType.ALL })
        @JoinTable(name = "user_group_rel", joinColumns = @JoinColumn(name = "mhs_user_id"), inverseJoinColumns = @JoinColumn(name = "group_id"))
        public List<Group> getGroups() {
                return groups;
        }
        public void setGroups(List<Group> groups) {
                this.groups = groups;
        }

}

In the above, mhs_user_id is the identity column in the MHS_USER table and grp_id is the identity key in the GROUP table. USER_GROUP_REL table is the join table that holds the relation between the two. When I persist a new User instance, it works as expected (by inserting a record into the parent table as well as the child table). However, when I try updating any values to the User instance, PropertyAccessException is thrown. Below is the selective stack trace

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[1/14/11 13:59:10:154 CST] 0000004b SystemErr     R Caused by: org.hibernate.PropertyAccessException: IllegalArgumentException occurred calling getter of edu.mayo.hcdm.mhsr.businessobject.Group.id
        at org.hibernate.property.BasicPropertyAccessor$BasicGetter.get(BasicPropertyAccessor.java:171)
        at org.hibernate.tuple.entity.AbstractEntityTuplizer.getIdentifier(AbstractEntityTuplizer.java:183)
………………………………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………………………………..
……………………………………………………………………………………………………………………………………………….. [1/14/11 13:59:10:154 CST] 0000004b SystemErr     R    ... 90 more
[1/14/11 13:59:10:154 CST] 0000004b SystemErr     R Caused by: java.lang.IllegalArgumentException: object is not an instance of declaring class
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79)
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It get's confusing as Hibernate throws an error that the "object is not an instance of declaring class" when searching for the group_id from the GROUP table only on updates. I found a lot of threads online about it being a hibernate bug (am using Hibernate 3.3.1). Has anyone encountered the same problem and if so, how did you end up solving it? Any input is highly appreciated.

Answer 1

确保groups列表中不包含Group以外的对象-这似乎是最明显的原因。