我对嵌套类的thymeleaf表单有问题。我正在做卡路里计数器的应用程序，当我试图添加一个新的食品产品到现有的一餐我得到一个例外。foodproduct是一个类，它处理所有foodproduct的模板，例如apple、chicken breast等。
食品类：

@Entity
@Table(name = "food_products")
public class FoodProduct {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

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

    @Column(name = "proteins")
    private Double proteins;

    @Column(name = "fats")
    private Double fats;

    @Column(name = "carbohydrates")
    private Double carbohydrates;

    @Column(name = "calories")
    private Double calories;

  // ...
}

mealfoodproduct类别：

@Entity
@Table(name = "meals_food_products")
@IdClass(MealFoodProductPK.class)
public class MealFoodProduct {

    @Id
    @ManyToOne
    @JoinColumn(name = "meal_id")
    private Meal meal;

    @Id
    @ManyToOne
    @JoinColumn(name = "food_product_id")
    private FoodProduct foodProduct;

    @Column(name = "food_product_weight")
    private double weight;

  //...
}

html表单：

<form action="#" th:action="@{/saveMealFoodProduct}" th:object="${mealFoodProduct}" method="post">

    <div>
        <label>Product name</label>
        <div>
            <select th:field="*{foodProduct}">
                <option th:each="foodProduct : ${foodProducts}" th:text="${foodProduct}" th:value="${foodProduct.id}"></option>
            </select>
        </div>

    </div>
    <div>
        <label>Weight</label>
        <div>
            <input type="number" th:field="*{weight}" placeholder="Enter weight">
        </div>
    </div>
    <br>
    <div>
        <div>
            <button type="submit">Save</button>
        </div>
    </div>
</form>

当我确认一张表格时，我有一个例外，我不知道怎么了：

Failed to convert property value of type 'java.lang.Integer' to required type 'pl.sosinski.nutritioncounter.model.FoodProduct' for property 'foodProduct';
 nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.Integer' to required type 'pl.sosinski.nutritioncounter.model.FoodProduct' for property 'foodProduct': no matching editors or conversion strategy found
org.springframework.beans.ConversionNotSupportedException: Failed to convert property value of type 'java.lang.Integer' to required type 'pl.sosinski.nutritioncounter.model.FoodProduct' for property 'foodProduct'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.Integer' to required type 'pl.sosinski.nutritioncounter.model.FoodProduct' for property 'foodProduct': no matching editors or conversion strategy found