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您好我正在尝试使用 HSQLDB、Spring、Webflow 和 JSF 开发宠物诊所应用程序。

其中BusinessEntities 层中的Vets 和Specialties 实体具有ManyToMany 关系，如下所示。

兽医.java

@Entity
@Table(name = "VETS", schema = "PUBLIC", catalog = "PUBLIC")
public class Vets implements BaseEntity, java.io.Serializable {

private Long id;
private String firstName;
private String lastName;
private Set<Specialties> specialtieses = new HashSet<Specialties>(0);

public Vets() {
}

public Vets(Long id) {
    this.id = id;
}

public Vets(Long id, String firstName, String lastName,
        Set<Specialties> specialtieses) {
    this.id = id;
    this.firstName = firstName;
    this.lastName = lastName;
    this.specialtieses = specialtieses;
}

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name = "ID", unique = true, nullable = false)
public Long getId() {
    return this.id;
}

public void setId(Long id) {
    this.id = id;
}

@Column(name = "FIRST_NAME", length = 30)
public String getFirstName() {
    return this.firstName;
}

public void setFirstName(String firstName) {
    this.firstName = firstName;
}

@Column(name = "LAST_NAME", length = 30)
public String getLastName() {
    return this.lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}

@ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
@JoinTable(name = "VET_SPECIALTIES", schema = "PUBLIC", catalog = "PUBLIC", joinColumns = { @JoinColumn(name = "VET_ID", nullable = false, updatable = false) }, inverseJoinColumns = { @JoinColumn(name = "SPECIALTY_ID", nullable = false, updatable = false) })
public Set<Specialties> getSpecialtieses() {
    return this.specialtieses;
}

public void setSpecialtieses(Set<Specialties> specialtieses) {
    this.specialtieses = specialtieses;
}

}

专业.java

@Entity
@Table(name = "SPECIALTIES", schema = "PUBLIC", catalog = "PUBLIC")
public class Specialties implements BaseEntity, java.io.Serializable {

private Long id;
private String name;
private Set<Vets> vetses = new HashSet<Vets>(0);

public Specialties() {
}

public Specialties(Long id) {
    this.id = id;
}

public Specialties(Long id, String name, Set<Vets> vetses) {
    this.id = id;
    this.name = name;
    this.vetses = vetses;
}

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name = "ID", unique = true, nullable = false)
public Long getId() {
    return this.id;
}

public void setId(Long id) {
    this.id = id;
}

@Column(name = "NAME", length = 80)
public String getName() {
    return this.name;
}

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

@ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
@JoinTable(name = "VET_SPECIALTIES", schema = "PUBLIC", catalog = "PUBLIC", joinColumns = { @JoinColumn(name = "SPECIALTY_ID", nullable = false, updatable = false) }, inverseJoinColumns = { @JoinColumn(name = "VET_ID", nullable = false, updatable = false) })
public Set<Vets> getVetses() {
    return this.vetses;
}

public void setVetses(Set<Vets> vetses) {
    this.vetses = vetses;
}

}

当我使用 setSpecialtieses 方法添加具有专业的 vets 对象时，填充了 vets、specialities 和 vet_secialities 表，但以前的关系正在丢失，让我这样说。

添加 ID 为 1 的 vet

 --------------        -----------------           --------------------
|   Vets        |     |   Specialities  |         |  vet_specialities  |
| --------------|     |-----------------|         |--------------------|
| ID    Name    |     | ID    Name      |         |Spe_ID      Vet_ID  |
| --------------|     |-----------------|         |--------------------|
| 1     ABC     |     | 1    Surgery    |         |  1          1      |
 --------------       | 2    Radiology  |         |  2          1      |
                       -----------------           --------------------

当我添加另一个 ID 为 2 的 Vet 对象时，

 --------------        -----------------           --------------------
|   Vets        |     |   Specialities  |         |  vet_specialities  |
| --------------|     |-----------------|         |--------------------|
| ID    Name    |     | ID    Name      |         |Spe_ID      Vet_ID  |
| --------------|     |-----------------|         |--------------------|
| 2     ABC     |     | 1    Surgery    |         |  1          2      |
 --------------       | 2    Radiology  |         |  2          2      |
                       -----------------           --------------------

在这里，我以前的条目被删除并存储了新条目，我的要求是也保留旧的兽医条目。

我有 vetsPage.xhtml，其中我有一个带有提交按钮的文本框和相应的 vets.xml 流，其条目创建新的 vetsVO 对象并使用 JPA 将其保存在 List 中，此时 Specialties 集为空，我有同样的方式specialitiesPage 带有一个文本框和提交按钮以及相应的流程，该流程还创建 SpecialitiesVO 对象并保存在 List 中，现在我还有一个页面，即 vetsSpecialitiesPage，我将从下拉列表中选择一个 vetsVO 对象并使用它映射专业并保存。通过这种方式，它可以适当地保存，但会覆盖现有的关系。尝试了几个建议，即使用 mappedBy、CascadeType.MERGE 等。但没有一个给出预期的结果。感谢任何帮助。

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