如何在JAVA JPA Spring Boot中的一个SQL查询中选择多个数据

Question

我有用户实体，其中包含组列表。每个组都有两个列表：submissionDocumentType和reviewDocumentType。使用尽可能少的数据库调用获取User的GroupDetails对象列表的最有效方法是什么（请参阅下面的最终预期结果）？

user.Java

public class User {
@Id
@GeneratedValue(generator ="uuid")
@GenericGenerator(name = "uuid", strategy = "uuid2")
private String id;

@ManyToMany(mappedBy = "users")
private Set<UserGroup> userGroups;

用户组

public class UserGroup {

@Id
@GeneratedValue(generator ="uuid")
@GenericGenerator(name = "uuid", strategy = "uuid2")
private String id;

@ManyToMany(mappedBy = "submissionUserGroups")
private List <DocumentType> submissionDocumentType;


@ManyToMany(mappedBy = "reviewUserGroups")
private List <DocumentType> reviewDocumentType;

group details.Java

public class GroupDetails {

private String groupTitle;
private List<String> reviewDocTypes;
private List<String> submitDocTypes;

GET方法的预期响应

[
{
    "groupTitle": "Group one",
    "reviewDocTypes": [
        "Prasymas Eazy",
        "Prasymas Tgwz",
        "Prasymas Gien",
        "Prasymas Docs",
        "Prasymas Ecyd",
        "Prasymas Sjvz"
    ],
    "submitDocTypes": [
        "Prasymas Buor",
        "Prasymas Kzhc",
        "Prasymas Zokx",
        "Prasymas Vvtb",
        "Prasymas Docs",
        "Prasymas Lutj",
        "atostogu prasymas"
    ]
},
{
    "groupTitle": "Group two",
    "reviewDocTypes": [
        "Prasymas Tgwz",
        "Prasymas Gien",
        "Prasymas Kzhc",
        "Prasymas Kblj",
        "Prasymas Docs",
        "Prasymas Ecyd"
    ],
    "submitDocTypes": [
        "Prasymas Tgwz",
        "Prasymas Wmwx",
        "Prasymas Buor",
        "Prasymas Gien",
        "Prasymas Kzhc",
        "Prasymas Kblj",
        "Prasymas Docs",
        "Prasymas Xdau",
        "Prasymas Lutj",
        "Prasymas Ecyd",
        "atostogu prasymas"
    ]
}
]

Answer 1

我想你可以在一个查询中做到这一点。正如你在the reference documentation中看到的：

Spring Data允许建模专用返回类型，以更有选择地检索托管聚合的部分视图。将查询结果限制为仅名称属性的最简单方法是声明一个接口，该接口公开要读取的属性的访问器方法

所以我们可以使用这样的查询方法获取结果：

interface UserRepository extends Repository<User, String> {
    Collection<GroupDetails> findById(String userId);
}