如何在Hibernate中的同一張表上做子查詢？

Question

我有一個名爲item_association的Oracle表和一個附帶的Hibernate實體。下面是該錶行的例子：

id group_id item_id type value 
==================================== 
1 1   1234  'lang' 'en' 
2 1   2345  'lang' 'fr' 

我想查詢該表檢索共享與特定ITEM_ID一個GROUP_ID所有ItemAssociations，並排除ITEM_ID本身。該SQL將是：

select group_id, item_id, type, value 
from ITEM_ASSOCIATION 
where group_id in (select group_id from ITEM_ASSOCIATION where item_id = :itemId) 
and item_id <> :itemId 

我嘗試使用下面的Hibernate的標準來實現這一點，但我得到：org.hibernate.MappingException: Unknown entity: null

DetachedCriteria subquery = DetachedCriteria.forClass(ItemAssociation.class) 
        .add(Restrictions.eq("itemId", itemId)) 
        .setProjection(Projections.property("groupId")); 

Criteria query = session.createCriteria(ItemAssociation.class) 
        .add(Property.forName("itemId").in(subquery)) 
        .add(Restrictions.not(Restrictions.eq("itemId", itemId))); 

ItemAssociation.java：

@Entity 
@Table(name = "ITEM_ASSOCIATION") 
public class ItemAssociation { 
    @Id 
    @GeneratedValue 
    private Long id; 

    @Column(name = "group_id") 
    private Long groupId; 

    @OneToOne 
    @JoinColumn(name = "item_id", insertable = false, updatable = false) 
    private Item item; 

    @Column 
    private String type; 

    @Column 
    private String value; 

    public Long getGroupId() { 
     return groupId; 
    } 

    public void setGroupId(Long groupId) { 
     this.groupId = groupId; 
    } 

    public Item getItem() { 
     return item; 
    } 

    public void setItemId(Item item) { 
     this.item = item; 
    } 

    public String getType() { 
     return type; 
    } 

    public void setType(String type) { 
     this.type = type; 
    } 

    public String getValue() { 
     return value; 
    } 

    public void setValue(String value) { 
     this.value = value; 
    } 

    public Long getId() { 
     return id; 
    } 

    public void setId(Long id) { 
     this.id = id; 
    } 
} 

Answer 1

這一個只是我的一個疏忽。由於ItemAssociation實體包含Item引用而不是itemId字段，因此我需要在我的查詢中將itemId更改爲item.id。此外，在query第一itemId應該是groupId：

DetachedCriteria subquery = DetachedCriteria.forClass(ItemAssociation.class) 
        .add(Restrictions.eq("item.id", itemId)) 
        .setProjection(Projections.property("groupId")); 

Criteria query = session.createCriteria(ItemAssociation.class) 
        .add(Property.forName("groupId").in(subquery)) 
        .add(Restrictions.not(Restrictions.eq("item.id", itemId))); 

Answer 2

使用有機.hibernate.criterion.Subqueries＃propertyIn（String propertyName，DetachedCriteria dc）

(...) 
Criteria query = session.createCriteria(ItemAssociation.class) 
       .add(Subqueries.propertyIn("itemId",subquery)) 
       .add(Restrictions.not(Restrictions.eq("itemId", itemId))); 
(...)