Spring MVC Error: Failed to convert property value

Question

I can't let this exception go:

Failed to convert property value of type java.lang.String to required type com.company.springdemo.entity.Product for property productId; nested exception is java.lang.IllegalStateException: Cannot convert value of type java.lang.String to required type com.company.springdemo.entity.Product for property productId: no matching editors or conversion strategy found 

Order Model

@Entity
@Table(name = "orders") // naming the table only order, will throw exception
public class Order {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "order_id")
private Integer orderId;


@OneToOne(cascade = {CascadeType.DETACH,CascadeType.MERGE,CascadeType.PERSIST,CascadeType.REFRESH})
@JoinColumn(name = "product_id")
private Product productId;

@ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.DETACH,CascadeType.MERGE,CascadeType.PERSIST,CascadeType.REFRESH})
@JoinColumn(name = "client_id")
private Client client;

....

Product Model

@Entity
@Table(name = "product")
public class Product {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "product_id")
private Integer id;

@Column(name = "product_name")
private String productName;

@Column(name = "product_serial")
private String productSerial;

...

Client Model

@Entity
@Table(name = "clients")
public class Client {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;

@NotEmpty
@Column(name = "first_name")
private String firstName;

@NotEmpty
@Column(name = "last_name")
private String lastName;

@NotEmpty
@Email
@Column(name = "email")
private String email;

@NotEmpty
@Column(name = "location")
private String location;

@OneToMany(mappedBy = "client",cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<Order> orders;

Controller, where I save the order with related client and product

@PostMapping("add")
public ModelAndView addOrder( @Validated @ModelAttribute("ords") Order order, BindingResult bindingResult ){

    if (bindingResult.hasErrors()) {
        System.out.println("Having errors: " + bindingResult.getAllErrors());

        Iterable<Product> products = productService.listProducts();
        Iterable<Client> clients = clientService.listClients();


        System.out.println("Error "+ bindingResult.getAllErrors());

        ModelAndView mv = new ModelAndView("orders/add-order");

        mv.addObject("products",products);
        mv.addObject("clients",clients);

        return mv;
    }

    try {
        orderService.saveOrder(order);
    } catch (Exception e) {
        e.printStackTrace();
    }

    ModelAndView mv = new ModelAndView("redirect:list");

    return mv;
}

Finally, my JSP form View page

<form:form action="add" method="post" modelAttribute="ords">

    <label for="productId" >Product Id</label>
    <form:select path="productId" >
        <c:forEach var="product" items="${products}">
            <form:option value="${product.id}">${product.productName}</form:option>
        </c:forEach>
    </form:select>

    <form:errors path="productId"/>

    <br>

    <label for="client" >Client Id</label>
    <form:select path="client" >
        <c:forEach var="client" items="${clients}">
            <form:option value="${client.id}">${client.id} - ${client.lastName}</form:option>
        </c:forEach>
    </form:select>

    <form:errors path="client"/>

    <br>

    <input type="submit" value="Place Order">

</form:form>

What am I doing wrong?

Answer 1

The productId field is actually a Product object, not an ID (String/int). You need your JSP to use path="productId.id" rather than path="productId".

(Although I'd also suggest you also rename the field product rather than productId.)

<form:select path="product.id">

I think you'll hit the same issue on your <form:select path="client"> too.

Answer 2

You most likely need to build a converter class such as this one :

@Component("facilityConverter")
public class FacilityConverter implements Converter<String, Facility>
{
    @Autowired
    FacilityService facilityService;

    @Override
    public Facility convert(String id) 
    {
        return facilityService.findById(Integer.parseInt(id));
    }
}

Then, you need to register it by implementing the addFormatters method inside of a configuration class implementing WebMvcConfigurer like so :

@Override
public void addFormatters (FormatterRegistry registry)
{
    registry.addConverter((FacilityConverter)ctx.getBean("facilityConverter"));
}

Your entities will then correctly be mapped from a dropdown selection. Also, this might not be part of your issue but you can just build your dropdowns like this :

<form:select name="linkedInterface" path="linkedInterface" id="linkedInterface">
                        <form:options items="${interfaces}" itemLabel="name" itemValue="id"/>
                    </form:select>