While coding in JPA with hibernate underneath I got an exception org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags. I was using “LIST” for the association and fetching eagerly

	@ManyToMany(cascade={CascadeType.MERGE,CascadeType.REFRESH},fetch = FetchType.EAGER)
	@JoinTable(name="class_subject", 
	joinColumns={@JoinColumn(name="classid")}, inverseJoinColumns=@JoinColumn(name="subjectid"))
	private List<SubjectDetails> subjects;

The problem seems to be two fold:

1. JPA allows only two level of nesting for collection, Parententity->Childentity is fine but it does not allow Parententity->childentity->SubChildEntity
2. Using List for collection instead of SET -remember a SET guarantees unique elements while list does not

What could be solution:

1. Use SET instead of List and thats what I have done for the moment

	private SET<SubjectDetails> subjects;