@OneToMany Spring Boot 2.1.5.RELEASE 中的 Spring Data JPA 没有获取所有数据答案

【问题标题】：@OneToMany Spring Data JPA in SpringBoot 2.1.5.RELEASE Does not get all data@OneToMany Spring Boot 2.1.5.RELEASE 中的 Spring Data JPA 没有获取所有数据
【发布时间】：2019-10-03 09:07:53
【问题描述】：

我有一个基本的 SpringBoot 2.1.5.RELEASE 应用程序。使用 Spring Initializer、JPA、嵌入式 Tomcat、Thymeleaf 模板引擎，并打包为可执行 JAR 文件。

我有这个域类：

@Entity
@Table(name="t_purchase")
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Purchase implements Serializable {

    public Purchase() {
    }

    public Purchase(Shop shop) {
        super();
        this.shop = shop;
    }

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

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = “shop_id")
    @JsonIgnore
    Shop shop;
…
}

还有

@Entity
@Table(name = “t_shop")
public class Shop implements Serializable {


    public Shop(String name) {
        this.name = name;
    }

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

    @JsonProperty("name")
    private String name;

    @OneToMany(mappedBy = “shop", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
    @JsonIgnore
    private Set<Purchase> purchases = new HashSet<Purchase>();

        …
}

以及仓库中的这个方法：

@Query("select shop from Shop shop left join shop.purchases where shop.id = ?1")
Shop shopPurchases (Long shopId);

然后我创建了这个 Junit 方法：

@Test
public void testFindByShopIdWithPurchases () {

    Shop shop = new Shop ("Shop_NAME");

    shopService.save(shop);

    Purchase purchase1 = new Purchase(shop);
    Purchase purchase2 = new Purchase(shop);

    shop.getPurchases().add(purchase1);
    shop.getPurchases().add(purchase2);

    shopService.save(shop);

    Shop shopWithPurchases = shopService.findByShopIdWithPurchases(shop.getId());

    assertEquals (2, shopWithPurchases.getPurchases().size());


}

但它失败了，因为它返回 1 个购买而不是 2 个

【问题讨论】：

标签： hibernate spring-boot jpa orm spring-data-jpa

【解决方案1】：

如果您为具有生成 id 的实体覆盖 equals，您需要处理两个 id 均为空的情况。否则 HashSet 会将新实体视为平等，并且只会存储一个。

在这种情况下你可以使用默认的equals：

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Purchase  other = (Purchase) obj;
    if(this.id == null) {
        if(other.id == null) {
            return super.equals(other);
        }
        return false;
    }
    return this.id.equals(other.id);
}

【讨论】：