java - Spring Roo 生成大量查询

Question

我正在尝试学习 Spring Roo，并且正在做我的小应用程序。 我有产品类别:

@RooJavaBean
@RooToString
@RooEntity(table = "TOWARY")
public class Product {
    @Id
    @GeneratedValue
    @Column(name = "ID")
    private int id;

    @Column(name = "NAZWA")
    private String name;

    @Version
    @Column(name = "VERSION")
    private int version;
}

还有一个事实类:

@RooJavaBean
@RooToString
@RooEntity(table = "FACTS")
public class Fact {
    @Id
    @GeneratedValue
    @Column(name = "ID")
    private int id;

    @Column(name = "KWOTA")
    private float kwota;

    @Column(name = "NCZAS")
    private int nczas;

    @Version
    @Column(name = "VERSION")
    private int version;

    @NotNull
    @ManyToOne(fetch=FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name="ID_TOWAR")
    private Product product;
}

在 Spring Roo 施展魔法后，我开始应用程序并看到网页。干得好，代码很少，而且几乎可以工作。
在进行产品预览时，它工作正常:

Hibernate: select product0_.ID as ID0_, product0_.NAZWA as NAZWA0_, product0_.VERSION as VERSION0_ from TOWARY product0_
Hibernate: select product0_.ID as ID0_, product0_.NAZWA as NAZWA0_, product0_.VERSION as VERSION0_ from TOWARY product0_ limit ?
Hibernate: select count(product0_.ID) as col_0_0_ from TOWARY product0_ limit ?

但是当我查看事实时，我有很多查询(基本上每个事实表行一个查询):

Hibernate: select fact0_.ID as ID1_, fact0_.KWOTA as KWOTA1_, fact0_.NCZAS as NCZAS1_, fact0_.ID_TOWAR as ID5_1_, fact0_.VERSION as VERSION1_ from FACTS fact0_
Hibernate: select product0_.ID as ID0_0_, product0_.NAZWA as NAZWA0_0_, product0_.VERSION as VERSION0_0_ from TOWARY product0_ where product0_.ID=?
Hibernate: select product0_.ID as ID0_0_, product0_.NAZWA as NAZWA0_0_, product0_.VERSION as VERSION0_0_ from TOWARY product0_ where product0_.ID=?
Hibernate: select product0_.ID as ID0_0_, product0_.NAZWA as NAZWA0_0_, product0_.VERSION as VERSION0_0_ from TOWARY product0_ where product0_.ID=?
...

经过搜索，我发现了“N+1选择问题”的帖子。我说得对吗——这也是我的问题吗？
我认为 @Fetch(FetchMode.JOIN) 强制 hibernate 使用 join 而不是子选择。

在方面文件中，我发现生成的查询负责获取我的数据:

public static List<Fact> Fact.findAllFacts() {
    return entityManager().createQuery("SELECT o FROM Fact o", Fact.class).getResultList();
}

如何强制 Spring Roo 使用 join？我做错了什么？

Answer 1

将 FetchType.EAGER 从 ManyToOne 更改为 FetchType.LAZY。预加载正在获取整个对象图。我非常确定您可以摆脱 @Fetch(FetchMode.JOIN) 注释。