Mysql 如何在JPA（不是JPQL）中选择实体的一部分？

我正在使用JPA2.0、Hibernate4.1.0.Final和MySQL5.5。我有两个班，小组和小组成员。GroupMember类链接到Group类，如下所示

public class GroupMember
{

    @Id
    @NotNull
    @GeneratedValue(generator = "uuid-strategy")
    @Column(name = "ID")
    private String id;

    @ManyToOne
    @JoinColumn(name = "USER_ID", nullable = false, updatable = true)
    private User user;

    @ManyToOne
    @JoinColumn(name = "GROUP_ID", nullable = false, updatable = true)
    private Group group;

如何编写JPA查询，以便获得用户所在的所有组？我很难只选择“组”，因为criteria子句是围绕GroupMember对象构建的

    final CriteriaBuilder builder = m_entityManager.getCriteriaBuilder();
    CriteriaQuery<GroupMember> criteria = builder.createQuery(GroupMember.class);
    final Root<GroupMember> groupMemberRoot = criteria.from(GroupMember.class);
    criteria.multiselect(groupMemberRoot.get(GroupMember_.group)).where(builder.equal(groupMemberRoot.get(GroupMember_.user), user));
    TypedQuery<Group> results = m_entityManager.createQuery(criteria);  // doesn’t compile

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最后一行没有编译，希望有人知道正确的语法是什么。

您的代码没有编译，因为您必须创建一个CriteriaQuery。试试这个：

final CriteriaBuilder builder = m_entityManager.getCriteriaBuilder();
CriteriaQuery<Group> criteria = builder.createQuery(Group.class);
final Root<GroupMember> groupMemberRoot = criteria.from(GroupMember.class);
criteria.select(groupMemberRoot.get(GroupMember_.group));
criteria.where(builder.equal(groupMemberRoot.get(GroupMember_.user), user));
TypedQuery<Group> results = m_entityManager.createQuery(criteria);

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未编译，可能有编译器错误消息。。。