我在两个实体之间有一个简单的关联 - Category和Email（NtoM）。我正在尝试创建用于浏览和管理它们的Web界面。我有一个简单的电子邮件订阅编辑表单，其中包含表示给定电子邮件所属类别的复选框列表（我注册了Set<Category>类型的属性编辑器）。
表格显示效果很好，包括标记当前指定的类别（针对现有电子邮件）。但是没有更改保存到EmailsCategories表（NtoM映射表，使用@JoinTable定义的表 - 未添加新检查的类别，也不会删除未选中的类别。
电子邮件实体：
@Entity
@Table(name = "Emails")
public class Email
{
@Id
@GeneratedValue(generator = "system-uuid")
@GenericGenerator(name = "system-uuid", strategy = "uuid2")
@Column(length = User.UUID_LENGTH)
protected UUID id;
@NaturalId
@Column(nullable = false)
@NotEmpty
@org.hibernate.validator.constraints.Email
protected String name;
@Column(nullable = false)
@Temporal(TemporalType.TIMESTAMP)
protected Date createdAt;
@Column
protected String realName;
@Column(nullable = false)
protected boolean isActive = true;
@ManyToMany(mappedBy = "emails", fetch = FetchType.EAGER)
protected Set<Category> categories = new HashSet<Category>();
public UUID getId()
{
return this.id;
}
public Email setId(UUID value)
{
this.id = value;
return this;
}
public String getName()
{
return this.name;
}
public Email setName(String value)
{
this.name = value;
return this;
}
public Date getCreatedAt()
{
return this.createdAt;
}
public String getRealName()
{
return this.realName;
}
public Email setRealName(String value)
{
this.realName = value;
return this;
}
public boolean isActive()
{
return this.isActive;
}
public Email setActive(boolean value)
{
this.isActive = value;
return this;
}
public Set<Category> getCategories()
{
return this.categories;
}
public Email setCategories(Set<Category> value)
{
this.categories = value;
return this;
}
@PrePersist
protected void onCreate()
{
this.createdAt = new Date();
}
}
类别实体：
@Entity
@Table(name = "Categories")
public class Category
{
@Id
@GeneratedValue(generator = "system-uuid")
@GenericGenerator(name = "system-uuid", strategy = "uuid2")
@Column(length = User.UUID_LENGTH)
protected UUID id;
@NaturalId(mutable = true)
@Column(nullable = false)
@NotEmpty
protected String name;
@ManyToMany
@JoinTable(
name = "EmailsCategories",
joinColumns = {
@JoinColumn(name = "idCategory", nullable = false, updatable = false)
},
inverseJoinColumns = {
@JoinColumn(name = "idEmail", nullable = false, updatable = false)
}
)
protected Set<Email> emails = new HashSet<Email>();
public UUID getId()
{
return this.id;
}
public Category setId(UUID value)
{
this.id = value;
return this;
}
public String getName()
{
return this.name;
}
public Category setName(String value)
{
this.name = value;
return this;
}
public Set<Email> getEmails()
{
return this.emails;
}
public Category setEmails(Set<Email> value)
{
this.emails = value;
return this;
}
@Override
public boolean equals(Object object)
{
return object != null
&& object.getClass().equals(this.getClass())
&& ((Category) object).getId().equals(this.id);
}
@Override
public int hashCode()
{
return this.id.hashCode();
}
}
控制器：
@Controller
@RequestMapping("/emails/{categoryId}")
public class EmailsController
{
@Autowired
protected CategoryService categoryService;
@Autowired
protected EmailService emailService;
@ModelAttribute
public Email addEmail(@RequestParam(required = false) UUID id)
{
Email email = null;
if (id != null) {
email = this.emailService.getEmail(id);
}
return email == null ? new Email() : email;
}
@InitBinder
public void initBinder(WebDataBinder binder)
{
binder.registerCustomEditor(Set.class, "categories", new CategoriesSetEditor(this.categoryService));
}
@RequestMapping(value = "/edit/{id}", method = RequestMethod.GET)
public String editForm(Model model, @PathVariable UUID id)
{
model.addAttribute("email", this.emailService.getEmail(id));
model.addAttribute("categories", this.categoryService.getCategoriesList());
return "emails/form";
}
@RequestMapping(value = "/save", method = RequestMethod.POST)
public String save(@PathVariable UUID categoryId, @ModelAttribute @Valid Email email, BindingResult result, Model model)
{
if (result.hasErrors()) {
model.addAttribute("categories", this.categoryService.getCategoriesList());
return "emails/form";
}
this.emailService.save(email);
return String.format("redirect:/emails/%s/", categoryId.toString());
}
}
表单视图：
<form:form action="${pageContext.request.contextPath}/emails/${category.id}/save" method="post" modelAttribute="email">
<form:hidden path="id"/>
<fieldset>
<label for="emailName"><spring:message code="email.form.label.Name" text="E-mail address"/>:</label>
<form:input path="name" id="emailName" required="required"/>
<form:errors path="name" cssClass="error"/>
<label for="emailRealName"><spring:message code="email.form.label.RealName" text="Recipient display name"/>:</label>
<form:input path="realName" id="emailRealName"/>
<form:errors path="realName" cssClass="error"/>
<label for="emailIsActive"><spring:message code="email.form.label.IsActive" text="Activation status"/>:</label>
<form:checkbox path="active" id="emailIsActive"/>
<form:errors path="active" cssClass="error"/>
<form:checkboxes path="categories" element="div" items="${categories}" itemValue="id" itemLabel="name"/>
<form:errors path="categories" cssClass="error"/>
<button type="submit"><spring:message code="_common.form.Submit" text="Save"/></button>
</fieldset>
</form:form>
（emailService.save()只是对emailDao.save()）
public void save(Email email)
{
this.getSession().saveOrUpdate(email);
}
一个简单的测试片段：
public void test()
{
Category category = new Category();
category.setName("New category");
this.categoryDao.save(category);
Email email = new Email();
email.setName("test@me")
.setRealName("Test <at> me")
.getCategories().add(category);
this.emailDao.save(email);
}
这些是日志：
12:05:34.173 [http-bio-8080-exec-23] DEBUG org.hibernate.SQL - insert into Emails (createdAt, isActive, name, realName, id) values (?, ?, ?, ?, ?)
12:05:34.177 [http-bio-8080-exec-23] DEBUG org.hibernate.persister.collection.AbstractCollectionPersister - Inserting collection: [pl.chilldev.mailer.web.entity.Category.emails#24d190e3-99db-4792-93ea-78c294297d2d]
12:05:34.177 [http-bio-8080-exec-23] DEBUG org.hibernate.persister.collection.AbstractCollectionPersister - Collection was empty
即使使用这些日志，它似乎有点噱头 - 它只是插入带有一个元素的集合，但它告诉它是空的......
答案 0 :(得分：29)
我们再来一次。
双向关联有两个方面：业主方和反方。所有者方是没有的mappedBy属性。要知道实体之间存在哪种关联，JPA / Hibernate只关心所有者方。您的代码仅修改反面，而不修改所有者。
保持对象图的一致性是你的工作。拥有一个不连贯的对象图有时是可以接受的，但不修改所有者方不会使更改持久。
所以你需要添加
category.getEmails().add(email);
或选择电子邮件作为所有者方而不是类别。