如何使 HATEOAS 渲染空嵌入数组

Question

通常

CollectionModel

将返回一个

_embedded

数组，但在本例中：

@GetMapping("/{id}/productMaterials")
    public ResponseEntity<?> getProductMaterials(@PathVariable Integer id) {
        Optional<Material> optionalMaterial = materialRepository.findById(id);
        if (optionalMaterial.isPresent()) {
            List<ProductMaterial> productMaterials = optionalMaterial.get().getProductMaterials();
            CollectionModel<ProductMaterialModel> productMaterialModels =
                    new ProductMaterialModelAssembler(ProductMaterialController.class, ProductMaterialModel.class).
                            toCollectionModel(productMaterials);
            return ResponseEntity.ok().body(productMaterialModels);
        }
        return ResponseEntity.badRequest().body("no such material");
    }

如果

productMaterials

为空，

CollectionModel

将不会渲染

_embedded

数组，这会破坏客户端。有什么办法可以解决这个问题吗？

Answer 1

if (optionalMaterial.isPresent()) {
        List<ProductMaterial> productMaterials = optionalMaterial.get().getProductMaterials();
        CollectionModel<ProductMaterialModel> productMaterialModels =
                new ProductMaterialModelAssembler(ProductMaterialController.class, ProductMaterialModel.class).
                        toCollectionModel(productMaterials);
        if(productMaterialModels.isEmpty()) {
            EmbeddedWrappers wrappers = new EmbeddedWrappers(false);
            EmbeddedWrapper wrapper = wrappers.emptyCollectionOf(ProductMaterialModel.class);
            Resources<Object> resources = new Resources<>(Arrays.asList(wrapper));
            return ResponseEntity.ok(new Resources<>(resources));
        } else {
            return ResponseEntity.ok().body(productMaterialModels);
        }
    }    

Answer 2

现在使用此代码可以轻松完成：

    List<ProductMaterial> productMaterials = optionalMaterial.get().getProductMaterials();
    return HalModelBuilder.emptyHalModel()
            .embed(productMaterials, ProductMaterial.class)
            .build();