Question

我在努力从充满对象的数组列表中获取属性。我想找到属于某个餐点的所有菜肴，并按盘类型进行筛选，并在视图的表格中显示它们。

所以我已经编写了getDishNameByType方法，但是它将返回null。任何帮助将不胜感激！

Meal.Java

public class Meal {

    @Id
    @GeneratedValue
    private Long id;

    @ManyToMany
    private Set<Dish> dishesList = new HashSet<>();


    public String getDishNameByType(String dishType) {  
        for (Dish dish : dishesList) {
            if (dishType == dish.getDishType()) {
                return dish.getDishName();
            }
        }
        return null;    
    }
}

Dish.Java

public class Dish {

    @Id
    @GeneratedValue
    private Long id;   

    private String dishName;

    private String dishType;

    @ManyToMany(mappedBy = "dishesList")
    private Set<Meal> mealsList = new HashSet<>();

View.html

<tr th:if="${mealPage.empty}">
    <td colspan="7" th:text="#{meals.list.table.empty}">No meals found</td>
</tr>
<tr th:each="meal : ${mealPage}">
    <td th:text="${meal.id}">1</td>
    <td th:each="dish : ${meal.dishesList}"
    th:text="${meal.getDishNameByType("Maincourse")}"></td>

</tr>

Answer 1

如果您有两个对象obj1和obj2，则当且仅当两个对象相同时，obj1 == obj2才是true。

String foo = "abc";
String bar = "abc";

boolean same = (foo == bar); //false
boolean similar = (foo.equals(bar)); //true

因此，您需要致电equals：

public String getDishNameByType(String dishType) {  
    for (Dish dish : dishesList) {
        if ((dishType.equals(dish.getDishType()))) {
            return dish.getDishName();
        }
    }
    return null;    
}

JPA如何从ManyToMany关系中的对象的数组列表中获取属性

1 个答案: