java - 嵌套对象空字段的 Spring 表单绑定(bind)问题

Question

我在使用 spring @ModelAttribute 表单绑定(bind)时遇到了一个相当尴尬的问题。我有以下实体类，它在表单绑定(bind)中用作策略类的嵌套类。

@javax.persistence.Entity
@Table(name = "entity")
@XmlRootElement
public class Entity implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "entity_id")
    private Integer entityId;

    @Basic(optional = false)
    @NotNull
    @Column(name = "entity_type")
    private int entityType;

    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 2147483647)
    @Column(name = "entity_name")
    private String entityName;

    public Entity() {
    }

    public Entity(Integer entityId) {
        this.entityId = entityId;
    }

    public Entity(Integer entityId, int entityType, String entityName) {
        this.entityId = entityId;
        this.entityType = entityType;
        this.entityName = entityName;
    }

    public Integer getEntityId() {
        return entityId;
    }

    public void setEntityId(Integer entityId) {
        this.entityId = entityId;
    }

    public int getEntityType() {
        return entityType;
    }

    public void setEntityType(int entityType) {
        this.entityType = entityType;
    }

    public String getEntityName() {
        return entityName;
    }

    public void setEntityName(String entityName) {
        this.entityName = entityName;
    }
}

我的问题的主要兴趣是 Policy 类，它是顶级类和主要绑定(bind)，如下所示:

@Entity
@Table(name = "policy")
@XmlRootElement
public class Policy implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "policy_id")
    private Integer policyId;

    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 2147483647)
    @Column(name = "reference_number")
    private String referenceNumber;

    @JoinColumn(name = "adjuster_id", referencedColumnName = "entity_id", nullable = true)
    @ManyToOne(optional = true)
    private Entity adjusterId;

    public Policy() {
    }

    public Policy(Integer policyId) {
        this.policyId = policyId;
    }

    public Integer getPolicyId() {
        return policyId;
    }

    public void setPolicyId(Integer policyId) {
        this.policyId = policyId;
    }

    public String getReferenceNumber() {
        return referenceNumber;
    }

    public void setReferenceNumber(String referenceNumber) {
        this.referenceNumber = referenceNumber;
    }


    public Entity getAdjusterId() {
        return adjusterId;
    }

    public void setAdjusterId(Entity adjusterId) {
        this.adjusterId = adjusterId;
    }
}

这是 Controller 方法，它从 View 绑定(bind)中获取带注释的 ModelAttribute Policy 参数。

@RequestMapping(value = "/create", method = RequestMethod.POST)
    public ModelAndView create(@ModelAttribute Policy p) {
        policyService.create(p);
        return new ModelAndView("viewName");
    }

最后，这是代码的表单/ View 部分:

<form id="policyInformationForm" role="form" th:object="${policy}" th:action="@{${mode == 'CREATE'} ? '/policy/create' : '/policy/update'}" method="post">
                        <div class="box-body">
                            <div class="form-group">
                                <label for="policyId">Policy Id</label>
                                <input type="text" th:field="*{policyId}" class="form-control" id="policyId" placeholder="" readonly="readonly" />
                            </div>

                            <div class="form-group">
                                <label for="referenceNumber">Policy Number (May change while saving!!!)</label>
                                <input type="text" th:field="*{referenceNumber}" class="form-control" id="referenceNumber" placeholder="Enter Policy Number" th:readonly="${mode == 'UPDATE'}" />
                            </div>

                            <div class="form-group">
                                <label for="adjusterName">Adjuster</label>
                                <div class="input-group">
                                    <input type="hidden" th:field="*{adjusterId.entityId}" class="form-control" id="adjusterId" />
                                    <input type="text" th:field="*{adjusterId.entityName}" class="form-control" id="adjusterName" placeholder="Enter Adjuster" />
                                    <div class="input-group-btn">
                                        <button id="adjusterSearchBtn" type="button" class="btn btn-success"><span class="glyphicon glyphicon-search"></span></button>
                                        <button id="adjusterCreateBtn" type="button" class="btn btn-success"><span class="glyphicon glyphicon-plus"></span></button>
                                    </div>
                                </div>
                            </div>

                        </div>

                        <div class="box-footer">
                            <button type="submit" class="btn btn-primary">Submit</button>
                            <a th:href="@{'/policy/list'}" class="btn btn-warning">Cancel</a>
                        </div>
                    </form>

问题出在我提交表单时； spring 表单绑定(bind)将表单参数绑定(bind)到 Policy 类的各个字段，但是如果未选择调整器，即 adjusterId 值的隐藏字段为空(这对于应用程序来说非常好)然后 spring 实例化一个新的实体类，所有字段都具有空值。由于 ManyToOne 关系和 JPA 验证，这会在应用程序的 JPA 持久性部分产生问题。

有关如何克服此问题的任何指示。如果 View (表单隐藏输入字段)中的 adjusterId 为空；那么表单绑定(bind)不应实例化具有空字段值的新实体类。相反，它应该将 Policy 类的 adjusterId 属性设置为 null。

顺便说一下，我已经回答过许多类似的问题，而这些问题中的大多数都不相关。其中之一就是 same question which is unanswered

提前致谢...

Answer 1

在 Controller 中，你可以这样做:

@RequestMapping(value = "/create", method = RequestMethod.POST)
public ModelAndView create(@ModelAttribute Policy p) {
    if (p.getAdjusterId().getEntityId() == null) {
        p.setAdjusterId(null);
    }
    policyService.create(p);
    return new ModelAndView("viewName");
}