使用Criteria API在Hibernate中選擇沒有父項的記錄

Question

如何使用Criteria API選擇沒有父項的記錄與Hibernate？

這裏是選擇我的Java代碼與父母

getSessionFactory().getCurrentSession().createCriteria(Category.class).add(
Restrictions.eq("parent", new Category(parentId))).list(); 

類別Java代碼

@Entity 
@Table(name = "CATEGORY") 
public class Category implements NamedModel{ 
    @Id 
    @Column(name = "CATEGORY_ID") 
    @GeneratedValue(strategy = GenerationType.AUTO) 
    private long id; 
    @OneToOne(cascade = CascadeType.REMOVE, fetch = FetchType.LAZY) 
    @JoinTable(name = "CATEGORY_RELATIONS", 
     joinColumns = { 
       @JoinColumn(name = "CATEGORY_RELATIONS_CATEGORY_ID", referencedColumnName = "CATEGORY_ID")}, 
     inverseJoinColumns = { 
       @JoinColumn(name = "CATEGORY_RELATIONS_PARENT_ID", referencedColumnName = "CATEGORY_ID")}) 
    private Category parent; 
    @OneToMany(cascade = CascadeType.REMOVE, fetch = FetchType.EAGER, mappedBy = "parent") 
    private List<Category> children;//... 
} 

CategoryRelations Java代碼

@Entity 
@Table(name = "CATEGORY_RELATIONS") 
@IdClass(CategoryRelations.CategoryRelationsPrimaryKey.class) 
public class CategoryRelations implements Serializable { 
    @Id 
    @Column(name = "CATEGORY_RELATIONS_CATEGORY_ID") 
    private long categoryId; 
    @Id 
    @Column(name = "CATEGORY_RELATIONS_PARENT_ID") 
    private long parentId; 

    @Entity 
    @IdClass(CategoryRelationsPrimaryKey.class) 
    public static class CategoryRelationsPrimaryKey implements Serializable { 
     private long categoryId; 
     private long parentId; 
    } 
} 

Answer 1

可以使用Restriction#isNull(propertyName)功能您的要求。

Restrictions.isNull("parent")