java - Hibernate 查询集合中的 ID 返回太多结果

Question

我有一个名为 Group 的实体类，它具有层次结构并使用 ID 引用来指示父级。我的 CriteriaQuery 返回太多结果(几乎所有组)，而且我无法弄清楚我错过了什么。

getChildrenNames()方法通常会触发log.warn()警告。

每个组可以有 1 个或多个由 Group.parentID 定义的父组。实际上，通常有 0 或 1 个 parent 。

public List<String> getChildrenNames(Group group) {
    CriteriaBuilder builder = getEntityManager().getCriteriaBuilder();
    CriteriaQuery<String> criteriaQuery = builder.createQuery(String.class);
    Root<Group> root = criteriaQuery.from(Group.class);

    criteriaQuery.where( createParentPredicate(group, criteriaQuery) );
    /*
     * Return only the group names not the entire Group entity 
     */
    criteriaQuery.select(root.get(GroupModelAttributes.COL_NAME));

    List<String> results = getEntityManager().createQuery(criteriaQuery).getResultList();

    if (results != null && results.size() > 100)
        log.warn("Detected unusually large number of children names for group \"%s\" COUNT: %d", 
                group.getName(), results.size());

    return results != null && results.size() > 0 ? results : null;
}

private Predicate createParentPredicate(Group group, CriteriaQuery<?> criteriaQuery) {
    String groupID = group.getID();
    Validate.notNull(groupID, "Group has no ID: " + group);
    String column = GroupModelAttributes.COL_PARENTIDS;
    CriteriaBuilder builder = getEntityManager().getCriteriaBuilder();
    Root<Group> root = criteriaQuery.from(Group.class);
    Expression<Collection<String>> colLoc = root.get(column);
    return builder.isMember(groupID, colLoc);
}

@Entity()
@Table(uniqueConstraints = { @UniqueConstraint(columnNames = { "name" }),
        @UniqueConstraint(columnNames = { "iD" }) }, name = "T_Group")
public class Group {
    @Basic()
    @Column(name = "ID")
    private String iD = null;

    @Basic()
    @Column(name = "Name")
    private String name = null;

    @ElementCollection(fetch = FetchType.EAGER)
    @Column(name = "T_element")
    @CollectionTable(joinColumns = { @JoinColumn(name = "Group_id") }, name = "Group_ParentIDs")
    private Set<String> parentIDs = new HashSet<String>();
}

Answer 1

我终于发现问题出在createParentPredicate()中，我创建了一个新的Root实例。这是有效的 createParentPredicate():

private Predicate createParentPredicate(Group group, Root<?> root) {
        String groupID = group.getID();
        Validate.notNull(groupID, "Group has no ID: " + group);
        String column = GroupModelAttributes.COL_PARENTIDS;

        return root.join(column).in(groupID);
}