Using linked Resources in Custom REST Controller with Spring REST JPA

Question

I am developing a set of rest resources over a database and exposing the core CRUD functionality using Spring Data Rest to directly interact with the Repositories.

In my simplified sample I have Users:

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public long id;

    public String name;

    @OneToMany(mappedBy = "user")
    public Collection<Project> projects;
}

and users Own Projects:

@Entity
public class Project {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public long id;

    public String name;

    public String oneOfManyComplexDerivedProperties;

    @ManyToOne
    public User user;
}

Directly interacting with the repositories is fine, so for creating Users (other other simple entities), the problem comes with creating Projects. Projects have a large number of server derived fields based on the users form input, so I wrote a custom controller to generate them and persist the result. In order to persist the result, I need to associate the Project with it's owning User. I want my client to be able to use the user Link for this, just as when creating a new entity by going direct to the repository (going direct to the repository just works):

@RepositoryRestController
public class CustomProjectController {

    @Autowired
    ProjectRepo projectRepo;

    @RequestMapping(value = "/createProject", method = RequestMethod.POST)
    public HttpEntity<Project> createProject(@RequestParam User userResource,
                                         @RequestParam String formField1, // actually an uploaded file that gets processed, but i want simple for example purposes
                                         @RequestParam String formfield2)
{
    Project project = new Project();

    /*
    Actually a large amount of complex business logic to derive properties from users form fields, some of these results are binary.
     */
    String result = "result";
    project.oneOfManyComplexDerivedProperties = result;
    project.user = userResource;
    projectRepo.save(project);

    // aware that this is more complex than I've written.
    return ResponseEntity.ok(project);
}
}

When I call:
http://localhost:9999/api/createProject?userResource=http://localhost:9999/api/users/1&formField1=data1&formField2=Otherdata

I get:

{
    "timestamp": 1510588643801,
    "status": 400,
    "error": "Bad Request",
    "exception": "org.springframework.web.method.annotation.MethodArgumentTypeMismatchException",
    "message": "Failed to convert value of type 'java.lang.String' to required type 'com.badger.User'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Long] for value 'http://localhost:9999/api/users/1'; nested exception is java.lang.NumberFormatException: For input string: \"http://localhost:9999/api/users/1\"",
    "path": "/api/createProject"
}

If I change userResource to type Resource then I get a different error:
"Failed to convert value of type 'java.lang.String' to required type 'org.springframework.hateoas.Resource'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'org.springframework.hateoas.Resource': no matching editors or conversion strategy found"

I can't find any reference to using repository URI's in custom controllers in the docs, the closest I found was Resolving entity URI in custom controller (Spring HATEOAS) but the API's have changed since that was written and I have not been able to get it to work.

Answer 1

I would suggest that what you should really be doing is:

http://localhost:9999/api/users/1/projects?formField1=data1&formField2=Otherdata

By enable Spring Data's web support you can have the path variable automatically bound to the entity instance.

@RequestMapping(value = "users/{id}/projects", method = RequestMethod.POST)
        public HttpEntity<Project> createProject(
                            @PathVariable("id") User user,
                            @RequestParam String formField1,
                            @RequestParam String formfield2)
{

}

https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#core.web

Answer 2

What User userResource requires is a User object what you passed in was a String http://localhost:9999/api/users/1

So I would recommend you changing your request to a POST request and passing your User Object as the body of that request.

The body of the request will look like in JSON format:

{
    id: 1,
    name: "myName",
    projects: []
}

so you then remove userResource=http://localhost:9999/api/users/1 from your URL. Finally change @RequestParam User userResource to @RequestBody User userResource

EDIT since you have the user Id in your request you can make a call within the controller to find the user by the Id. So you can change the user object from @RequestParam User userResource to @RequestParam long userId then make a call to find the user something like findUserById(userId) inside your method

so you url will look like http://localhost:9999/api/createProject?userId=1&formField1=data1&formField2=Otherdata

Answer 3

If you want to stick with the url params you could change the @RequestParam User userResource to @RequestParam String userId

And then in your createProject code have something along the lines of

User user = userRepo.findOne(userId);
project.user = user;
....
projectRepo.save(project);

If it was me I'd define a CreateProjectRequest object which you pass in, e.g.

{
   "userId" : "1",
   "formField1" : "whatever",
   "formField2" : "whatever"
}

And change your createProject to

createProject(@RequestBody CreateProjectRequest createProjectRequest)
    ...
    project.setField1(createProjectRequest.getFormField1());
    ...

    User user = userRepo.findOne(createProjectRequest.getUserId());
    project.user = user;
    ....
    projectRepo.save(project);