如何从 JSP 页面保存 JPA 实体模型属性的特定属性

Question

我们在 jsp 页面上使用 JPA 实体 bean 作为 Spring MVC 控制器的模型。我们的 jsp 页面之一是该实体的部分视图，它不显示所有属性。每当我们尝试使用来自控制器的服务层来更新我们的实体时，只有在 jsp 表单上使用的属性会被持久化，而所有其他属性都会被清空。处理这种情况的正确方法是什么？我们不想在表单上指定隐藏字段。

所以在这种情况下，当控制器调用 service.update(client) 方法时，name 字段将为 null，因为它在 form.jsp 中不存在。

form.jsp

<form:form modelAttribute="client" method="get" action="${action}">
<table width="100%">
    <tr>
        <td>
            <table>
                <tr>
                    <td valign="top"><spring:message code="label.tradeOrderManagementSystem"/>:</td>
                    <td>
                        <form:select path="tradeOrderManagementSystems" >
                            <form:options items="${tradeOrderManagementSystemList}" itemValue="id" itemLabel="name" />
                        </form:select>
                        <a href="<spring:url value="/tradeOrderManagementSystem/add"/>" class="addAndReturn"><span><spring:message code="add"/></span></a>
                    </td>
                    <td>
                        <form:errors path="tradeOrderManagementSystems" cssClass="errors" />
                    </td>
                </tr>
                <tr><td></td><td>&nbsp;</td></tr>
            </table>
        </td>
    </tr>
</table>
<input type="hidden" name="submitted" value="true">

控制器

@RequestMapping("/{id}/edit")
public ModelAndView edit(HttpServletRequest request,
        HttpServletResponse response,
        @ModelAttribute("client") Client client,
        BindingResult result,
        @PathVariable("id") int id,
        Model model) {
    ControllerContext ctx = new ControllerContext(request, response);
    init(ctx);

    setAdvancedSearchAvailable(ctx, true);
    buildShowAndEditVerticalMenu(ctx, id, false);

    if (id == 0) {
        result.addError(new ObjectError("client", getMessage("error.idNeeded")));
        return getModelAndView(ctx, "itEfficiencies/form");
    } else {
        if (!isSubmission(ctx)) {
            client = clientService.find(id);
            model.addAttribute("client", client);
            fillClientForm(model);
            return getModelAndView(ctx, "itEfficiencies/form");
        } else {
            //clientValidator.validate(client, result);
            if (result.hasErrors()) {
                fillClientForm(model);
                return getModelAndView(ctx, "itEfficiencies/form");
            } else {
                try {
                    //checkClientProperties(client);
                    client.setId(id);
                    client = clientService.update(client);  //method updates only form fields and nulls out all others
                } catch (Exception e) {
                    e.printStackTrace();
                    result.addError(new ObjectError("client", getMessage("error.save")));
                    fillClientForm(model);
                    return getModelAndView(ctx, "itEfficiencies/form");
                }
                return getModelAndView(ctx, "/staffingByClient/" + client.getId() + "/show", true);
            }
        }
    }
}    

Client.java

@Entity
public class Client extends AbstractEntity<Integer> {

private static final long serialVersionUID = 1L;

public static final String FIND_BY_NAME = "Client.FIND_BY_NAME";

public static final String COUNT_BY_NAME = "Client.COUNT_BY_NAME";

@Basic(optional = false)
@Column(nullable = false, length = 125)
private String name;

@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(inverseJoinColumns = {
    @JoinColumn(name = "trade_order_management_system_id")}, uniqueConstraints =
@UniqueConstraint(name = "UK_client_trade_order_mgmt_client_id_trade_order_mgmt_id",
columnNames = {"client_id", "trade_order_management_system_id"}))
@ForeignKey(name = "FK_client_trade_order_management_systems_client_id",
inverseName = "FK_client_trade_order_mgmt_sys_trade_order_management_system_id")
private List<TradeOrderManagementSystem> tradeOrderManagementSystems;

public Client() {
}

public Client(Integer id) {
    this.id = id;
}

public Client(Integer id, String name) {
    this.id = id;
    this.name = name;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}   

public List<TradeOrderManagementSystem> getTradeOrderManagementSystems() {
    return tradeOrderManagementSystems;
}

public void setTradeOrderManagementSystems(List<TradeOrderManagementSystem> tradeOrderManagementSystems) {
    this.tradeOrderManagementSystems = tradeOrderManagementSystems;
}

@Override
public boolean equals(Object object) {
    // TODO: Warning - this method won't work in the case the id fields are not set
    if (!(object instanceof Client)) {
        return false;
    }
    Client other = (Client) object;
    if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
        return false;
    }
    return true;
}

}

服务方法

public abstract class CrudService<T, ID extends Serializable> extends DAOImpl<T, ID> {

/**
 * Updates an entity from an existing entity.
 *
 * @since 0.0.1
 * 
 * @param entity
 * @return the managed instance of the updated entity
 */
@Override
@Transactional(rollbackFor = Exception.class, isolation = Isolation.READ_COMMITTED)
public T update(T entity, ID id) {
    return super.update(assignDefaultValues(entity), id);
}

}

public abstract class DAOImpl<T, ID extends Serializable> implements DAO<T, ID> {

private Class<T> persistentClass;

@PersistenceContext(unitName = "krfsPersistenceUnit")
protected EntityManager entityManager;

/**
 * Instantiates an instance of this class and sets the <code>persistentClass</code>
 * based on the identifier type
 *
 * @since 0.0.1
 */
public DAOImpl() {
    this.persistentClass = (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0];
}

/**
 * @since 0.0.1
 * 
 * @return the type to be persisted
 */
@Override
public Class<T> getPersistentClass() {
    return persistentClass;
}

/**
 * Updates an entity from an existing entity.
 *
 * @since 0.0.1
 * 
 * @param entity
 * @param id the identifier of the entity
 * 
 * @return the managed instance of the updated entity
 */
@Override
public T update(T entity, ID id) {
    //Find a managed instance of the entity first and copy the properties
    //to the passed in entity before merging.  This ensures that entityManager
    //will not create a new entity with merge.
    Object ref = this.entityManager.getReference(persistentClass, id);
    if (ref != null) {
        BeanUtils.copyProperties(entity, ref);
    }
    return (T) this.entityManager.merge(ref);
}

}

Answer 1

您并没有真正提供足够的详细信息（具体来说，显示您如何从表单中保存值的代码会有所帮助）但我怀疑您正在合并一个具有null 属性的分离实体。由于merge 的工作方式（它将分离实体的状态复制到具有相同数据库标识符的实体上，并加载到持久性上下文中），您会得到 NULL。

您需要：

• 以某种方式保留分离的实体，将表单中的值复制到其中，然后merge它〜或〜
• 实现“手动合并”，即使用实体 id 加载要更新的实体，从模型中复制新值并让 JPA 更新它。

如果我错过了重点，请提供更多详细信息以了解问题。

更新：我不明白你的代码。您正在复制属性从 ref 到 entity（来自视图的分离客户端），然后合并ref...不，我不这样做不明白。