How to post and publish links using Spring HATEOAS

Question

I am trying to understand how to create and modify links in Spring HATEOAS.

For example, let's say I have two collections, one for api / users and one for api / event. I would like to associate the api / user / 56 user with the api / event / 21 event. For arguments, this is a lot to many - a user can attend many events, an event can have many users.

As I understand it, a cool way to do this is to use URIs as primary keys, so I can publish the following in api / user / 56 / events;

{ attends: "http://localhost:9090/api/event/21" } 

Then the endpoint should be able to parse this URL and retrieve the identifier (in this case 21) and the controller (EventController.class) so that I can save this.

Question 1: Is this the correct way to relate relationships in Spring Hateoas in terms of a REST API?

Question 2: How can I resolve this URL in the controller to a useful data descriptor (for example, a link to the corresponding controller / method, primary key, etc.).

Study

RestTemplate can be used to request data from the controller inside the query matching method, for example:

 RestTemplate restTemplate = new RestTemplate(); ResponseEntity<EventResource> response = restTemplate.getForEntity(attendsUrl, EventResource.class); EventResource eventResource = response.getBody(); 

However, I do not think that eventResource should return an Id field as part of the data - it does not really calm down, and this will be displayed in the API. One approach is to have the parameter "includePK = true", but again this does not seem to be correct - it just hides the problem. Moreover, the idea of ​​a server making requests to it with its own API looks cool.

Update

There is an open question here: https://github.com/spring-projects/spring-hateoas/issues/292 . Based on some comments (from the user kevinconaway ) of this problem, I made a quick util class that offers an easy solution here: SpringHateoasUtils . The solution comes down to:

 String mapping = DISCOVERER.getMapping(targetClass, targetMethod); UriTemplate template = new UriTemplate(mapping); //values is key/value map of parameters that the referenced method accepts Map<String, String> values = uriTemplate.match(uri); 

SpringHateoasUtils makes this a bit nicer, but it still seems like it should be a function. I will try to get something in the Spring code for this - when it is clear what is happening with this, I will answer this question.

Answer 1

Take a look at the answer here:

@OneToMany resource POST connection in Spring Data REST

Question 1) Yes, this is how you post links / relationships. With a URI.

Question 2) The resource URI is actually its identifier from the point of view of the client. The server internally automatically resolves this URI to an instance of the actual model using

org.springframework.data.rest.core.UriToEntityConverter.convert(...)