如何在Spring Boot中使用Hibernate/JPA返回多级json

Question

我有一个Postgres数据库，有4个表父母，孩子，组和Group_Membership。

组可以有多个父母，父母可以有多个组。父母可以有多个孩子，但孩子只能有一个父母。

我正在使用Spring Boot和Hibernate JPA。

Parent.java

@Entity
@Table(name = "parents")
public class Parent {
    @Id
    @GeneratedValue
    @Column(name="parent_id")
    private Long parentId;
    @Column(name= "first_name")
    private String firstName;
    @Column(name= "last_name")
    private String lastName;
    @OneToMany(mappedBy="parent")
    private Set<Child> children;
    @ManyToMany(cascade = { CascadeType.ALL })
    @JoinTable(
            name= "Group_Membership",
            joinColumns = { @JoinColumn(name = "parent_id") },
            inverseJoinColumns = { @JoinColumn(name = "group_id") }
    )
    private Set<Group> groups = new HashSet<>();

    //Constructor 
    //Getters and Setters
}

Child.java

@Entity
@Table(name = "children")
public class Child {
    @Id
    @GeneratedValue
    @Column(name= "child_id")
    private Long childId;
    @Column(name= "first_name")
    private String firstName;
    @Column(name= "last_name")
    private String lastName;
    @ManyToOne
    @JoinColumn(name="parent_id", nullable=false)
    private Parent parent;

    //Constructor 
    //Getters and Setters
}

Group.java

@Entity
@Table(name = "groups")
public class Group {
    @Id
    @GeneratedValue
    @Column(name= "group_id")
    private Long groupId;
    private String name;
    @ManyToMany(mappedBy = "groups")
    private Set<Parent> parents = new HashSet<>();

    //Constructor 
    //Getters and Setters
}

我为所有这些文件建立了如下存储库：

public interface GroupRepository extends PagingAndSortingRepository<Group, Long> {
    @RestResource(rel = "name-contains", path = "containsName")
    Page<Group> findByNameContains(@Param("name") String name, Pageable page);
}

集团成员表

CREATE TABLE GROUP_MEMBERSHIP (
  PARENT_ID INT NOT NULL,
  GROUP_ID INT NOT NULL,
  PRIMARY KEY (PARENT_ID, GROUP_ID),
  CONSTRAINT GROUP_MEMBERSHIP_IBFK_1
   FOREIGN KEY (PARENT_ID) REFERENCES PARENTS (PARENT_ID),
  CONSTRAINT GROUP_MEMBERSHIP_IBFK_2
   FOREIGN KEY (GROUP_ID) REFERENCES GROUPS (GROUP_ID)
);

当我去http://localhost:8080/groups

我得到的回应是：

{
  "_embedded": {
    "groups": [
      {
        "name": "Hyde Park",
        "_links": {
          "self": {
            "href": "http://localhost:8080/groups/1"
          },
          "group": {
            "href": "http://localhost:8080/groups/1"
          },
          "parents": {
            "href": "http://localhost:8080/groups/1/parents"
          }
        }
      }
    ]
  },
  "_links": {
    "self": {
      "href": "http://localhost:8080/groups"
    },
    "profile": {
      "href": "http://localhost:8080/profile/groups"
    },
    "search": {
      "href": "http://localhost:8080/groups/search"
    }
  },
  "page": {
    "size": 20,
    "totalElements": 1,
    "totalPages": 1,
    "number": 0
  }
}

然后当我想看看我所在小组的父母时http://localhost:8080/groups/1/parents

回答

{
  "_embedded": {
    "parents": [
      {
        "firstName": "Cherice",
        "lastName": "Giannoni",
        "_links": {
          "self": {
            "href": "http://localhost:8080/parents/1"
          },
          "parent": {
            "href": "http://localhost:8080/parents/1"
          },
          "groups": {
            "href": "http://localhost:8080/parents/1/groups"
          },
          "children": {
            "href": "http://localhost:8080/parents/1/children"
          }
        }
      },
      {
        "firstName": "Aylmer",
        "lastName": "Feckey"
        "_links": {
          "self": {
            "href": "http://localhost:8080/parents/2"
          },
          "parent": {
            "href": "http://localhost:8080/parents/2"
          },
          "groups": {
            "href": "http://localhost:8080/parents/2/groups"
          },
          "children": {
            "href": "http://localhost:8080/parents/2/children"
          }
        }
      }
    ]
  },
  "_links": {
    "self": {
      "href": "http://localhost:8080/groups/1/parents"
    }
  }
}

最后，当我想看到第一个家长的孩子在我去的小组http://localhost:8080/parents/1/children

回答

{
  "_embedded": {
    "children": [
      {
        "firstName": "Richard",
        "lastName": "Giannoni"
        "_links": {
          "self": {
            "href": "http://localhost:8080/children/2"
          },
          "child": {
            "href": "http://localhost:8080/children/2"
          },
          "parent": {
            "href": "http://localhost:8080/children/2/parent"
          }
        }
      },
      {
        "firstName": "Deeanne",
        "lastName": "Giannoni"
        "_links": {
          "self": {
            "href": "http://localhost:8080/children/1"
          },
          "child": {
            "href": "http://localhost:8080/children/1"
          },
          "parent": {
            "href": "http://localhost:8080/children/1/parent"
          }
        }
      }
    ]
  },
  "_links": {
    "self": {
      "href": "http://localhost:8080/parents/1/children"
    }
  }
}

我希望能够调用一个endpoint，比如http://localhost:8080/groups/search/findAllGroupMembers?group_id=1

并让它返回组、组中的所有父级以及每个父级的所有子级的多级json。

我知道如何编写带有子查询的查询来返回这些信息，但我只是好奇是否有一种更“JPA/Hibernate”的方法来实现这一点？

谢谢！

编辑：使用Alan Hay的答案修复

集体投射。JAVA

@Projection(name = "groupFullProjection", types = {Group.class})
public interface GroupFullProjection {
    Long getGroupId();
    String getName();
    Set<ParentFullProjection> getParents();
}

rojection.java

@Projection(name = "parentFullProjection", types = {Parent.class})
public interface ParentFullProjection {
    Long getParentId();
    String getFirstName();
    String getLastName();
    Set<Child> getChildren();
}

包含所有必需信息的json响应

终点：http://localhost:8080/groups/1?projection=groupFullProjection

{
  "name": "Hyde Park",
  "groupId": 1,
  "parents": [
    {
      "children": [
        {
          "firstName": "Richard",
          "lastName": "Giannoni",
        },
        {
          "firstName": "Deeanne",
          "lastName": "Giannoni",
        }
      ],
      "parentId": 1,
      "firstName": "Cherice",
      "lastName": "Giannoni",
      "_links": {
        "self": {
          "href": "http://localhost:8080/parents/1{?projection}",
          "templated": true
        },
        "groups": {
          "href": "http://localhost:8080/parents/1/groups"
        },
        "children": {
          "href": "http://localhost:8080/parents/1/children"
        }
      }
    },
    {
      "children": [
        {
          "firstName": "Hanson",
          "lastName": "Feckey",
        }
      ],
      "parentId": 2,
      "firstName": "Aylmer",
      "lastName": "Feckey",
      "_links": {
        "self": {
          "href": "http://localhost:8080/parents/2{?projection}",
          "templated": true
        },
        "groups": {
          "href": "http://localhost:8080/parents/2/groups"
        },
        "children": {
          "href": "http://localhost:8080/parents/2/children"
        }
      }
    }
  ],
  "_links": {
    "self": {
      "href": "http://localhost:8080/groups/1"
    },
    "group": {
      "href": "http://localhost:8080/groups/1{?projection}",
      "templated": true
    },
    "parents": {
      "href": "http://localhost:8080/groups/1/parents"
    }
  }
}

Answer 1

懒惰/急切的加载与此毫无关系。应用程序中的REST服务是由Spring Data REST提供的，了解它为什么会这样以及如何更改它可能是值得学习的。

https://docs.spring.io/spring-data/rest/docs/current/reference/html/#repository-资源。基本原理

基本上，您可以获得到关联的链接，因为这些实体有自己的存储库，它们作为REST响应公开。如果子级/父级未作为REST资源公开，那么数据将被内联（因为没有其他方式访问它们）。

但是，您可以使用投影来获取数据的其他视图。这样你就可以定义一个投影，它可以嵌入Assocation。客户端可以请求数据的这种特定视图。

例如http://localhost:8080/groups/1?projection=groupFullProjection

这涉及到创建一个简单的接口，定义要在该数据视图中公开的属性。

见：https://docs.spring.io/spring-data/rest/docs/current/reference/html/#projections-节选

这可能看起来像：

@Projection(name = "parentFullProjecton", types = { Parent.class })
interface ParentFullProjection{

    // inline the child collection
    Set<Child> getChildren();

    // other fields
}

@Projection(name = "groupFullProjection", types = { Group.class })
interface GroupFullProjection{

    //inline the parents collection and use the view which inlines Children
    Set<ParentFullProjecton> getParent();

    // other fields
}