java - 将一对多文件传递给 NEW-Statement 构造函数

Question

我有以下类(class)

@NamedQueries({
        @NamedQuery(name = "User.FindByFilter", query = "SELECT NEW myPkg.SimpleUser(u.name , u.email, u.roles) FROM User u WHERE UPPER(u.name) LIKE :filter AND  ORDER BY u.name")
 })
@Entity
@Table(name = "Users")
public class User implements Serializable, UserDetails {
    @Id
    private String email;
    @Basic
    private String name;
    @OneToMany(cascade = { CascadeType.REFRESH, CascadeType.PERSIST }, fetch = FetchType.EAGER)
    private Set<Authority> roles;
...
}

和

@Entity
public class Authority implements GrantedAuthority {
//just @Id and @Basic here no specific mapping back to user
...
}

我当然知道这个查询

@NamedQuery(name = "User.FindByFilter", query = "SELECT NEW myPkg.SimpleUser(u.name , u.email, u.roles) FROM User u WHERE UPPER(u.name) LIKE :filter AND  ORDER BY u.name")

是错误的，因为u.roles是@OneToMany。
所以我的问题是将 Roles 字段传递给 const 的正确方法是什么？

Answer 1

来自JPA 2.0 specification ，它使用 single_valued_object_field 和 collection_valued_field 分别表示单个实体字段和集合实体字段:

A single_valued_object_field is designated by the name of an association field in a one-to-one or many-to-one relationship or a field of embeddable class type. The type of a single_valued_object_field is the abstract schema type of the related entity or embeddable class.

A collection_valued_field is designated by the name of an association field in a one-to-many or a many-to-many relationship or by the name of an element collection field. The type of a collection_valued_field is a collection of values of the abstract schema type of the related entity or element type.

然后它定义了具有以下语法的 SELECT 子句:

• constructor_expression ::= NEW constructor_name ( constructor_item {, constructor_item}* )

• constructor_item ::= single_valued_path_expression | scalar_expression | aggregate_expression | identification_variable

由于 constructor_item 可以接受 single_valued_pa​​th_expression 但不能接受 collection_valued_field ，我认为 new() 不能接受集合字段参数。

您必须使用 fetch 连接来检索 User 实例及其 Authority 集合，然后手动将其转换为 myPkg.SimpleUser