spring boot resource as links - spring

Question

I am new to spring boot, I have used it to implement a rest API. I have a self referencing table where each item has a parent -tree structure- . I have used ManyToOne to implement this and i get a json object which holds the parent. If i get all the items the speed is very slow since there are a huge network latency and processing because my tree can hold up to 10000 item.
How can I represent this using links, i.e the the json object contains a link to parent and array of links to children. I have read that DTO can be used to implement this but I did not find a full details.
part of my code
#Entity
#Table(name = "Item", schema = "dbo")
#Getter
#Setter
public class Item {
#Id
#GeneratedValue
#Column()
private Integer ItemID;
#Column()
private String Project;
#Column()
private String Name;
#Column()
private Integer Version;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "ParentItemID", insertable = false, updatable = false)
private Item parentItem;
My controller is strait forward
#Autowired
ItemService ItemService;
#RequestMapping ("/items")
public Iterable<Item> items(#RequestParam(value = "page", defaultValue = "0") Integer page,
#RequestParam(value = "size", defaultValue = "20") Integer size, Authentication auth) {
return ItemService.findPaginated(page, size);
}
I would be glad if i get more explanation on how to use DTOs , or another design to get links instead of full objects.

Answer 1

Easiest thing you can do is, return parent and children ids instead of Item objects.
#Entity
#Table(name = "Item", schema = "dbo")
public class Item {
.
.
private Integer ItemID;
private Integer parentItem;
.
.
Have another endpoint in your controller like /items/{itemId}
#GetMapping("/items/{itemId}")
public Item item(#PathVariable itemId, Authentication auth) {
return ItemService.findById(itemId);
Let your consumer grab the parent/children Ids and make separate REST calls
Alternatively, you can use Spring-HATEOAS
The Spring HATEOAS project is a library of APIs that we can use to
easily create REST representations that follow the principle of
HATEOAS (Hypertext as the Engine of Application State).
Generally speaking, the principle implies that the API should guide
the client through the through the application by returning relevant
information about the next potential steps, along with each response.
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