Spring HATEOAS RepresentationModelAssembler toCollectionModel()

Question

I'm creating Spring Boot HATEOAS REST application. Code below shows how am I adding links, while GET request is send for specific Employee. I'm using RepresentationModelAssembler toModel function. There's also toCollectionModel function to Override, which I would like to use to convert List<Employees> to CollectionModel. -> This will be returned in /Employees/all endpoint.

And I dunno how to do that. So what I need is to pass List<Employees>, then all list elements needs to be processed by toModel functions, and then, like in toModel function I need possibility to add more links to it -> links to entire new collection (not individual items).

Looking forward for your answers!

@Component
public class EmployeeModelAssembler implements RepresentationModelAssembler<Employee, EntityModel<Employee>> {

    @Override
    public EntityModel<Employee> toModel(Employee employee) {
        EntityModel<Employee> employeeEntityModel = EntityModel.of(employee);

        Link selfLink = linkTo(methodOn(EmployeeController.class).getEmployeeById(employee.getId())).withSelfRel();
        employeeEntityModel.add(selfLink);

        return employeeEntityModel;
    }

    @Override
    public CollectionModel<EntityModel<Employee>> toCollectionModel(Iterable<? extends Employee> entities) {

        ?? ?? ??

    }
}

Harikesh Harikesh · Accepted Answer · 2020-07-25T19:49:09

You can use something like this:

@GetMapping(produces = { "application/hal+json" })
public CollectionModel<Customer> getAllCustomers() {
    List<Customer> allCustomers = customerService.allCustomers();
 
    for (Customer customer : allCustomers) {
        String customerId = customer.getCustomerId();
        Link selfLink = linkTo(CustomerController.class).slash(customerId).withSelfRel();
        customer.add(selfLink);
        if (orderService.getAllOrdersForCustomer(customerId).size() > 0) {
            Link ordersLink = linkTo(methodOn(CustomerController.class)
              .getOrdersForCustomer(customerId)).withRel("allOrders");
            customer.add(ordersLink);
        }
    }
 
    Link link = linkTo(CustomerController.class).withSelfRel();
    CollectionModel<Customer> result = CollectionModel.of(allCustomers, link);
    return result;
}

Visit https://www.baeldung.com/spring-hateoas-tutorial#springhateoasinaction for detailed explanation

Spring HATEOAS RepresentationModelAssembler toCollectionModel()

1 Answers