Question

我正在尝试在Spring Boot中使用QueryDSL，它工作得很好，直到我碰到一个我找不到答案的问题。假设我有以下结构：

+-------+          +----------+          +-------+
| foo   |          | foo_bar  |          | bar   |
+-------+          +----------+          +-------+
| id    | -------->| foo_id   |       +- | id    |
| name  |          | bar_id   |<------|  | name  |
+-------+          | position |          +-------+
                   +----------+

我正在尝试使用QueryDSL中的Projections来管理我的服务响应，因此我将类定义为：

让Foo.class

@Entity
@Table(name = "foo")
public class Foo{

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, length = 100)
    private String name;

    // Relations

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "foo")
    private List<FooBar> fooBars;

    // Getters and Setters
}

FooBar.class

@Entity
@Table(name = "foo_bar")
public class AlbumView{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private int position;

    @ManyToOne(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
    @JoinColumn(name = "foo_id")
    private Foo foo;

    @ManyToOne(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
    @JoinColumn(name = "bar_id")
    private Bar bar;

    // Getters and Setters
}

Bar.class

@Entity
@Table(name = "bar")
public class Bar{

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, length = 100)
    private String name;

    // Relations

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "bar")
    private List<FooBar> fooBars;

    // Getters and Setters
}

现在在我的控制器中，我正在尝试执行以下代码，以Foo返回FooBars，其中Bar id为1.查询类型有效，因为它仅返回Foo id等于1的Bar，但我不知道如何获取关系表中的position属性。

JPQLQuery query = new JPAQuery(entityManager);
QFoo foo = QFoo.foo;
QFooBar fooBar = QFooBar.fooBar;

return query.from(foo)
        .join(foo.fooBars, fooBar).on(fooBar.bar.id.eq((long)1))
        .list(Projections.bean(Foo.class,
                foo.id,
                foo.name,
                Projections.bean(FooBar.class,
                        ???
                        // foo.fooBars.position can't be used because fooBars is an array
                        // foo.fooBars.get(0).position can't be used because i throws NullPointerException
                ).as("fooBars")
            )
        );

提前致谢。

使用QueryDSL with Spring

0 个答案: