计算实体子项的CriteriaQuery会产生格式错误的数字常量：。错误

Question

我在数据库中有以下表格。所有都用我的Java代码中的Hibernate注释表示。

|LibraryItem Table             |
|LibraryItemId|LibraryItemTitle|

|ItemListing Table                              |
|ListingId|ChildLibrayItemId|ParentLibraryItemId|

所以基本上有库项目。并且每个库项目可以是另一个库项目的子项或父项，并且该关系存储在项目列表表中。

我试图使用CriteriaBuilder方法获取特定库项目的所有子项的计数。这是我的代码：

public int getNumChildren(LibraryItem libItem) {
        CriteriaBuilder builder = sessionFactory.getCriteriaBuilder();
        CriteriaQuery<Long> query = builder.createQuery(Long.class);
        Root<LibraryItem> root = query.from(LibraryItem.class);
        query.select(builder.count(root.get("itemChildren")));
        query.where(builder.equal(root.get("libraryItemId"), libItem.getLibraryItemId()));
        return Math.toIntExact(sessionFactory.getCurrentSession().createQuery(query).uniqueResult());
    }

这会产生以下错误：

java.sql.SQLSyntaxErrorException: malformed numeric constant: . in statement [select count(.) as col_0_0_ from library_item libraryite0_, ITEM_LISTING itemchildr1_, library_item libraryite2_ where libraryite0_.LIBRARY_ITEM_ID=itemchildr1_.PARENT_LIB_ITEM_ID and itemchildr1_.CHILD_LIB_ITEM_ID=libraryite2_.LIBRARY_ITEM_ID and libraryite0_.LIBRARY_ITEM_ID=4601]

有人可以向我解释我在这里做错了吗？

编辑：

这是实体类。我省略了一些我认为无关的代码：

@Entity
@Table(name = "library_item", uniqueConstraints = {
        @UniqueConstraint(columnNames={"LIBRARY_ITEM_TITLE", "LIBRARY_ID"})

})
public class LibraryItem extends DatabaseObject {

    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "hilo_sequence_generator")
    @GenericGenerator(
            name = "hilo_sequence_generator",
            strategy = "org.hibernate.id.enhanced.SequenceStyleGenerator",
            parameters = {
                    @org.hibernate.annotations.Parameter(name = "sequence_name", value = "hilo_seqeunce"),
                    @org.hibernate.annotations.Parameter(name = "initial_value", value = "1"),
                    @org.hibernate.annotations.Parameter(name = "increment_size", value = "100"),
                    @org.hibernate.annotations.Parameter(name = "optimizer", value = "hilo")
            })
    @Id
    @Column(name = "LIBRARY_ITEM_ID", unique = true, nullable = false)
    private Long libraryItemId;

    @Column(name = "LIBRARY_ITEM_TITLE", nullable = false)
    private String libraryItemTitle;

    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "ITEM_LISTING",
            joinColumns = {@JoinColumn(name = "PARENT_LIB_ITEM_ID", nullable=false)},
            inverseJoinColumns = {@JoinColumn(name="CHILD_LIB_ITEM_ID", nullable = false)})
    private Set<LibraryItem> itemChildren = new HashSet<>();

    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "itemChildren")
    private Set<LibraryItem> itemParents = new HashSet<>();
}

Answer 1

您在多值字段上使用count。这在JPQL中是无效的，因此在Criteria中也是如此。

这样做的方法是使用size函数（CriteriaBuilder.size），它明确用于集合字段。