重置子p:selectOneMenus在ap:dataTable中为空,当选择其父列表中的标签项时

Question

在MySQL数据库中有三个表category,sub_category和brand(制造商)其中category是其余的父,即sub_category和brand.我希望,菜单之间的关系可以根据表关系更清晰.

所有三个<p:selectOneMenu>都被放置<p:dataTable>在三个相应的列中,如下所示<p:column>.我忽略<p:column>,<p:cellEditor>,<f:facet name="output">,<f:facet name="input">,<p:rowEditor>和所有这些滋扰赘述.

_{row对应于这是一个JPA管理实体product在这种情况下,通过指定var="row"在<p:dataTable>关联的.}

这是实际的问号:当一个项目(第一个)null的值categoryList被选择(母公司),其子清单subCategoryList和brandList应该休息了个空.

分类清单:

<p:selectOneMenu id="categoryList"
                 value="#{row.category}"
                 required="#{param['javax.faces.source'] ne component.clientId}">

    <f:selectItem itemLabel="Select"
                  itemValue="#{null}"/>
    <!-- When this item is selected, its children below should be reset to empty. -->

    <f:selectItems var="category"
                   value="#{productManagedBean.categories}"
                   itemLabel="Select"
                   itemValue="#{category}"/>

    <p:ajax update="subCategoryList brandList"/>
    <!-- The listener functionality is left incomplete here. -->
</p:selectOneMenu>

子类别列表:

<p:selectOneMenu id="subCategoryList"
                 value="#{row.subCategory}">

    <f:selectItem itemLabel="Select"
                  itemValue="#{null}"/>

    <f:selectItems var="subCategory"
                   value="#{productManagedBean.getSubCategories(row.category)}"
                   itemLabel="#{subCategory.subCatName}"
                   itemValue="#{subCategory}"
                   rendered="true"/>
</p:selectOneMenu>

品牌(制造商)清单:

<p:selectOneMenu id="brandList"
                 value="#{row.brand}">

    <f:selectItem itemLabel="Select"
                  itemValue="#{null}"/>

    <f:selectItems var="brand"
                   value="#{productManagedBean.getBrands(row.category)}"
                   itemLabel="#{brand.brandName}"
                   itemValue="#{brand}"
                   rendered="true"/>
</p:selectOneMenu>

托管bean(在此问题的上下文中可以忽略惰性数据模型):

@Named
@ViewScoped
public class ProductManagedBean extends LazyDataModel<Product> implements Serializable {

    @Inject
    private Service service;

    // Associated with <p:selectOneMenu id="categoryList">.
    private List<Category> categories; // Getter & setter.

    // These are merely helper maps to reduce possible database calls.
    private Map<Category, List<SubCategory>> subCategoriesByCategory;
    private Map<Category, List<Brand>> brandByCategory;

    public ProductManagedBean() {}

    @PostConstruct
    private void init() {
         // This can be application scoped somewhere else as per business requirement.
        categories = service.getCatgeoryList();

        subCategoriesByCategory = new HashMap<Category, List<SubCategory>>();
        brandByCategory = new HashMap<Category, List<Brand>>();
    }

    // This method populates <f:selectItems> associated with <p:selectOneMenu id="brandList">.

    public List<SubCategory> getSubCategories(Category category) {
        // category is never null here unless something is broken deliberately.

        if (category == null) {
            return null;
        }

        List<SubCategory> subCategories = subCategoriesByCategory.get(category);

        if (subCategories == null) {
            subCategories = service.findSubCategoriesByCategoryId(category.getCatId());
            subCategoriesByCategory.put(category, subCategories);
        }

        return subCategories;
    }

    // This method populates <f:selectItems> associated with <p:selectOneMenu id="brandList">.
    public List<Brand> getBrands(Category category) {
        // category is never null here unless something is broken deliberately.

        if (category == null) {
            return null;
        }

        List<Brand> brands = brandByCategory.get(category);

        if (brands == null) {
            brands = service.findBrandsByCategoryId(category.getCatId());
            brandByCategory.put(category, brands);
        }

        return brands;
    }
}

在任何情况下,任何这些菜单中的选定值都不会提供给相应的辅助bean.它仅适用于由JPA(支持的模型value="#{row.category}",value="#{row.subCategory}"并value="#{row.brand}"分别).

►如何选择辅助bean,null选择父菜单中带有值(标记为"选择")的第一个项目,以便将其子列表重置为空？如果不可行,这应该以任何可行的方式发生.

我正在使用PrimeFaces 5.2 final(社区发布)和Mojarra 2.2.12.

---

_{除非在底层数据库表中存在空外键,否则不需要这样做,具体使用供应商特定ON DELETE SET NULL选项,允许每个(或某些)相应子行中包含可选父项.}

Answer 1

就这一点而言，您需要确保使用参数<f:selectItem>调用 getter null。换句话说，#{row.category}必须是null。鉴于您要#{row.category}使用此答案中所示的模型，请根据 ap:dataTable 的每一行中的另一个 p:selectOneMenu 填充 p:selectOneMenu，最有可能如下所示，

@Transient
private Category category;

public Category getCategory() {
    return (category == null && subCategory != null) ? subCategory.getCategory() : category;
}

那么当存在 时，#{row.category}实际上永远不会存在。当现有数据条目呈现在视图中时就会出现这种情况。nullsubCategory

当瞬态属性显式设置为 null时，您基本上需要显式将subCategory( 和) 清空。与此同时，这一疏忽已在上述答案中得到修复。您的新方法应如下所示：brandcategorysetCategory()

public void setCategory(Category category) {
    this.category = category;

    if (category == null) {
        subCategory = null;
        brand = null;
    }
}

这样，意志getCategory()就会正确返回null，因此传入的#{row.category}也会正确返回。