问题描述
我有两张桌子。
DATA
+------+--------+---------------------+------------+
| ID | Name | Desc | Type |
+------+--------+---------------------+------------+
| 1001 | Motor | Main motor 50 volt | Mechanical |
| 1002 | Nut | 25 mm dia | Mechanical |
| 1003 | Bolt | Hexa bolt | Mechanical |
| 1004 | Engine | 750cc liquid cooled | Mechanical |
| 1005 | Oil | 1 liter | NA |
| 1006 | Filter | Airfilter | NA |
| 1007 | AC | 1000w | Electrical |
+------+--------+---------------------+------------+
Relationship
+-----------+-----------+----------+
| Parent_id | Relation | Child_id |
+-----------+-----------+----------+
| 1001 | Accessory | 1002 |
| 1001 | Accessory | 1003 |
| 1001 | Service | 1005 |
| 1001 | Service | 1006 |
| 1004 | Accessory | 1002 |
| 1004 | Accessory | 1003 |
| 1004 | Service | 1005 |
+-----------+-----------+----------+
{
"id": "1001","name": "Motor","desc": "Main motor 50 volt","Accessory": [{
"id": "1002","name": "Nut"
},{
"id": "1003","name": "Bolt"
}
],"Service": [{
"id": "1005","name": "Oil"
},{
"id": "1006","name": "Filter"
}
]
}
这里的 Accessory 和 Service 来自 relationship 表列 relation。我对弹簧靴一无所知。在谷歌的帮助下，我完成了以下代码。这给了我一个级别的 json。但我无法找到如何创建这个嵌套的 JSON。请提供一些建议。
存储库：
@Repository
public interface MyDataRepo extends JpaRepository<Items,String> {
@Query(value="SELECT D.id,D.name,D.desc,R.relation,R.child_id as childid,DC.name as childname
FROM DATA D
JOIN RELATIONSHIP R ON D.ID=R.PARENT_ID
JOIN DATA DC ON DC.id=R.CHILD_ID
WHERE D.ID=?1",nativeQuery=true)
List<Data> findAllCategory(String id);
public static interface Data {
String getid();
String getname();
String getdesc();
String getrelation();
String getchildid();
String getchildname();
}
}
服务：
public List<Data> getMyData(String id) {
return repo.findAllCategory(id);
}
控制器：
@GetMapping("/getData/{id}")
public ResponseEntity<List<Data>> retrieveData(@PathVariable String id) {
List<Data> stud = service.getMyData(id);
return ResponseEntity.ok().body(stud);
}
解决方法
由于Relation字段是动态的，我们无法使用POJO生成相关对象，所以我选择了一个Map对象来生成最终结果。
@GetMapping("/getData/{id}")
public ResponseEntity<Map<String,Object>> retrieveData(@PathVariable("id") Long id) {
List<MyDataRepo.Data> stud = myDataRepo.findAllCategory(id);
Map<String,Object> parent = new HashMap<>();
parent.put("id",stud.get(0).getid());
parent.put("name",stud.get(0).getname());
parent.put("desc",stud.get(0).getdesc());
stud.forEach(d -> {
String r = d.getrelation();
Map<String,String> child = new HashMap<>();
child.put("id",d.getchildid());
child.put("name",d.getchildname());
if (parent.containsKey(r)) {
List<Map<String,String>> children = (List<Map<String,String>>) parent.get(r);
children.add(child);
} else {
List<Map<String,String>> children = new ArrayList<>();
children.add(child);
parent.put(r,children);
}
});
return ResponseEntity.ok().body(parent);
}
最终得到结果
{
"id": "1001","name": "Motor","desc": "Main motor 50 volt","Accessory": [
{
"id": "1002","name": "Nut"
},{
"id": "1003","name": "Bolt"
}
],"Service": [
{
"id": "1005","name": "Oil"
},{
"id": "1006","name": "Filter"
}
]
}
要构建嵌套投影，您应该在实体之间建立关系，例如：
@Entity
@Table(name = "Data")
public class Data {
@Id
private long id;
@Column(name = "name")
private String name;
@Column(name = "desc")
private String desc;
@OneToMany(mappedBy = "parentId",fetch = FetchType.LAZY,cascade = CascadeType.ALL)
private Set<Relationship> relationship;
...getters/setters...
}
@Entity
@Table(name = "Relationship")
@IdClass(RelationshipId.class)
public class Relationship {
@Id
@Column(name = "parent_id")
private long parentId;
@Id
@Column(name = "relation")
private String name;
@Id
@Column(name = "child_id")
private long childId;
@OneToOne
@JoinColumn(name = "child_id",unique = true,nullable = false,updatable = false,insertable = false)
private Data child;
...getters/setters...
}
这是复合键的 id 类：
public class RelationshipId implements Serializable {
private long parentId;
private String name;
private long childId;
// default constructor
public RelationshipId(long parentId,String name,long childId) {
this.parentId = parentId;
this.name = name;
this.childId = childId;
}
// equals() and hashCode()
}
之前，我检查了两个选项：@IdClass 和@EmbeddedId。 我认为为您使用 @IdClass 注释更合适的方法。 详细说明：https://www.baeldung.com/jpa-composite-primary-keys
以下预测：
public interface DataView {
String getId();
String getName();
String getDesc();
List<RelationshipView> getRelationship();
}
public interface RelationshipView {
String getId();
String getName();
String getChildId();
DataItemView getChild();
}
public interface DataItemView {
String getId();
String getName();
String getDesc();
}
在 repo 中，您可以通过单个查询接收所有需要的数据，并将数据重组为适当的 DTO 视图：
public interface DataRepo extends JpaRepository<Data,String> {
@Query(value = "SELECT d from Data d " +
"left join fetch d.relationship as r " +
"left join fetch r.child as c " +
"where d.id=:id")
DataView getDataViewById(long id);
}
@Service
public class DataService {
@Autowired
private DataRepo dataRepo;
public DataDto getMyData(long id) {
DataView data = dataRepo.getDataViewById(id);
DataDto dataDto = new DataDto();
dataDto.setId(data.getId());
dataDto.setName(data.getName());
dataDto.setDesc(data.getDesc());
for (RelationshipView rs : data.getRelationship()) {
DataItemView dataItemView = rs.getChild();
switch (rs.getName()) {
case "Accessory":
dataDto.getAccessory().add(new DataItemDto(dataItemView.getId(),dataItemView.getName()));
break;
case "Service":
dataDto.getService().add(new DataItemDto(dataItemView.getId(),dataItemView.getName()));
break;
}
}
return dataDto;
}
}
DTO 的课程：
public class DataDto {
String id;
String name;
String desc;
List<DataItemDto> accessory = new LinkedList<>();
List<DataItemDto> service = new LinkedList<>();
...getters/setters...
}
public class DataItemDto {
String id;
String name;
public DataItemDto(String id,String name) {
this.id = id;
this.name = name;
}
...getters/setters...
}