Java 如果不使用泛型,请确保在关系映射上定义了目标实体
我是JPA新手,从中学习 我创建了两个表,一个是Java 如果不使用泛型,请确保在关系映射上定义了目标实体,java,jpa,mapping,Java,Jpa,Mapping,我是JPA新手,从中学习 我创建了两个表,一个是Person,另一个是Notebook。如果没有弄错,如果代码运行成功,将创建个人笔记本。(如果我错了,请纠正我,因为我是JPA新手) 人 @Entity @Table(name = "Person") @XmlRootElement @NamedQueries({ @NamedQuery(name = "Person.findAll", query = "SELECT p FROM Person p") , @NamedQu
Person
,另一个是Notebook
。如果没有弄错,如果代码运行成功,将创建个人笔记本。(如果我错了,请纠正我,因为我是JPA新手)
人
@Entity
@Table(name = "Person")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "Person.findAll", query = "SELECT p FROM Person p")
, @NamedQuery(name = "Person.findById", query = "SELECT p FROM Person p WHERE p.id = :id")
, @NamedQuery(name = "Person.findByName", query = "SELECT p FROM Person p WHERE p.name = :name")
, @NamedQuery(name = "Person.findByCompName", query = "SELECT p FROM Person p WHERE p.compName = :compName")})
public class Person implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id")
private Integer id;
@Basic(optional = false)
@Column(name = "Name")
private String name;
@Basic(optional = false)
@Column(name = "CompName")
private String compName;
@ManyToMany
@JoinTable(name="person_has_notebooks", joinColumns={@JoinColumn(name="person_id")}, inverseJoinColumns={@JoinColumn(name="notebook_id")})
private List notebooks;
public List getNotebooks() {
return notebooks;
}
public void setNotebooks(List notebooks) {
this.notebooks = notebooks;
}
public Person() {
}
public Person(Integer id) {
this.id = id;
}
public Person(Integer id, String name, String compName) {
this.id = id;
this.name = name;
this.compName = compName;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCompName() {
return compName;
}
public void setCompName(String compName) {
this.compName = compName;
}
@Override
public int hashCode() {
int hash = 0;
hash += (id != null ? id.hashCode() : 0);
return hash;
}
@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 Person)) {
return false;
}
Person other = (Person) object;
if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
return false;
}
return true;
}
@Override
public String toString() {
return "entity.Person[ id=" + id + " ]";
}
}
笔记本电脑
@Entity
@Table(name = "NoteBook")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "NoteBook.findAll", query = "SELECT n FROM NoteBook n")
, @NamedQuery(name = "NoteBook.findById", query = "SELECT n FROM NoteBook n WHERE n.id = :id")
, @NamedQuery(name = "NoteBook.findBySerialName", query = "SELECT n FROM NoteBook n WHERE n.serialName = :serialName")
, @NamedQuery(name = "NoteBook.findByRam", query = "SELECT n FROM NoteBook n WHERE n.ram = :ram")
, @NamedQuery(name = "NoteBook.findByHd", query = "SELECT n FROM NoteBook n WHERE n.hd = :hd")})
public class NoteBook implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id")
private Integer id;
@Basic(optional = false)
@Column(name = "SerialName")
private String serialName;
@Basic(optional = false)
@Column(name = "Ram")
private int ram;
@Basic(optional = false)
@Column(name = "HD")
private int hd;
@ManyToMany(mappedBy="notebooks")
private List person;
public List getPersons() {
return person;
}
public void setPersons(List persons) {
this.person = persons;
}
public NoteBook() {
}
public NoteBook(Integer id) {
this.id = id;
}
public NoteBook(Integer id, String serialName, int ram, int hd) {
this.id = id;
this.serialName = serialName;
this.ram = ram;
this.hd = hd;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getSerialName() {
return serialName;
}
public void setSerialName(String serialName) {
this.serialName = serialName;
}
public int getRam() {
return ram;
}
public void setRam(int ram) {
this.ram = ram;
}
public int getHd() {
return hd;
}
public void setHd(int hd) {
this.hd = hd;
}
@Override
public int hashCode() {
int hash = 0;
hash += (id != null ? id.hashCode() : 0);
return hash;
}
@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 NoteBook)) {
return false;
}
NoteBook other = (NoteBook) object;
if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
return false;
}
return true;
}
@Override
public String toString() {
return "entity.NoteBook[ id=" + id + " ]";
}
}
ManyToMany1
public class ManyToMany1 {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("ManyToMany1PU");
EntityManager em = emf.createEntityManager();
em.getTransaction().begin();
NoteBook noteA = new NoteBook();
noteA.setSerialNumber("A0123");
NoteBook noteB = new NoteBook();
noteB.setSerialNumber("B0123");
NoteBook noteC = new NoteBook();
noteC.setSerialNumber("C0123");
List notebooks = new ArrayList();
notebooks.add(noteA);
notebooks.add(noteB);
notebooks.add(noteC);
Person person = new Person();
person.setName("Zorro");
person.setNotebooks(notebooks);
em.persist(person);
em.getTransaction().commit();
}
}
错误
Exception Description: Predeployment of PersistenceUnit [ManyToMany1PU] failed.
Internal Exception: Exception [EclipseLink-7214] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.ValidationException
Exception Description: The target entity of the relationship attribute [notebooks] on the class [class entity.Person] cannot be determined. When not using generics, ensure the target entity is defined on the relationship mapping.
at org.eclipse.persistence.exceptions.PersistenceUnitLoadingException.exceptionSearchingForPersistenceResources(PersistenceUnitLoadingException.java:127)
at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactoryImpl(PersistenceProvider.java:107)
at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactory(PersistenceProvider.java:177)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:79)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:54)
at manytomany1.ManyToMany1.main(ManyToMany1.java:27)
我已经将
mappedBy
分配给了薄弱环节,但为什么仍然会出现这样的错误 为什么不按照消息告诉你的那样使用泛型呢
@ManyToMany
@JoinTable(name="person_has_notebooks", joinColumns={@JoinColumn(name="person_id")}, inverseJoinColumns={@JoinColumn(name="notebook_id")})
private List<NoteBook> notebooks;
@manytomy
@JoinTable(name=“person\u has\u notebooks”,joinColumns={@JoinColumn(name=“person\u id”)},inverseJoinColumns={@JoinColumn(name=“notebook\u id”)})
私人名单笔记本;
及
@ManyToMany(mappedBy=“笔记本”)
私人名单人士;
为什么不按照消息告诉您的那样使用泛型呢
@ManyToMany
@JoinTable(name="person_has_notebooks", joinColumns={@JoinColumn(name="person_id")}, inverseJoinColumns={@JoinColumn(name="notebook_id")})
private List<NoteBook> notebooks;
@manytomy
@JoinTable(name=“person\u has\u notebooks”,joinColumns={@JoinColumn(name=“person\u id”)},inverseJoinColumns={@JoinColumn(name=“notebook\u id”)})
私人名单笔记本;
及
@ManyToMany(mappedBy=“笔记本”)
私人名单人士;
正如错误所述,当不使用泛型时,您必须告诉提供者您指的是哪个实体。Neil Stockton下面的答案有一个如何使用泛型的例子。有一个例子,如果您不能或不想使用泛型,那么可以指定目标实体,因为JPA不知道您在引用什么类
@ManyToMany(targetEntity=com.example.NoteBook.class)
@JoinTable(name="person_has_notebooks", joinColumns={@JoinColumn(name="person_id")}, inverseJoinColumns={@JoinColumn(name="notebook_id")})
private List notebooks;
@ManyToMany(mappedBy="notebooks", targetEntity=com.example.Person.class)
private List person;
否则,如果您可以在列表中使用泛型,请使用Neils answer。错误说明,当不使用泛型时,您必须告诉提供者您引用的是哪个实体。Neil Stockton下面的答案有一个如何使用泛型的例子。有一个例子,如果您不能或不想使用泛型,那么可以指定目标实体,因为JPA不知道您在引用什么类
@ManyToMany(targetEntity=com.example.NoteBook.class)
@JoinTable(name="person_has_notebooks", joinColumns={@JoinColumn(name="person_id")}, inverseJoinColumns={@JoinColumn(name="notebook_id")})
private List notebooks;
@ManyToMany(mappedBy="notebooks", targetEntity=com.example.Person.class)
private List person;
否则,如果您可以在列表中使用泛型,请使用Neils答案。您的
@Entity
类注释在哪里?@OrtomalaLokni编辑。您为什么不使用泛型?在90年代开始编程是一个非常糟糕的主意。我会寻找更好的教程。如果这是在2011年写的,而且它没有使用泛型,谁知道它还包含了什么可怕的东西。那么Hibernate的网页呢?我只能告诉你,那是垃圾。你的@Entity
类注释在哪里?@OrtomalaLokni编辑。你为什么不使用泛型?在90年代开始编程是一个非常糟糕的主意。我会寻找更好的教程。如果这是在2011年写的,而且它没有使用泛型,谁知道它还包含了什么可怕的东西。那么Hibernate的网页呢?我可以告诉你的是,那是垃圾。如果他在学习一个不使用泛型的教程,那么最好是放弃整个教程。@JoinColumn(name=“person\u id”
和@JoinColumn(name=“notebook\u id”
。这两个列名与person\u has\u notebook
?@Kayaman@JoinColumn(name=“person\u id”和@JoinColumn(name=“notebook\u id”)中的列名相同。这两个列名与person_has_notebook中的列名相同?@JohnJoe我告诉过你找一个更好的教程。谢谢你的回答,但是我在同步过程中得到,通过一个未标记为cascade PERSIST:entity.notebook[noteBookid=null]的关系找到了一个新对象.
错误。错误指向em.getTransaction().commit();
如果他遵循的是一个不使用泛型的教程,那么可能最好放弃整个教程。@JoinColumn(name=“person\u id”
和@JoinColumn(name=“notebook\u id”
。这两个列名与person\u has\u notebook
?@Kayaman@JoinColumn(name=“person\u id”和@JoinColumn(name=“notebook\u id”)中的列名相同。这两个列名与person_has_notebook中的列名相同?@JohnJoe我告诉过你找一个更好的教程。谢谢你的回答,但是我在同步过程中得到,通过一个未标记为cascade PERSIST:entity.notebook[noteBookid=null]的关系找到了一个新对象.
错误。错误指向em.getTransaction().commit();
感谢您的回答。我使用Neils的答案,但在同步过程中,通过未标记为cascade PERSIST:entity.NoteBook[noteBookid=null]的关系找到了一个新对象。错误指向em.getTransaction().commit()
这是一个新问题,可能是因为在调用persist之前向关系中添加了一个实体。在设置关系之前,可以对两个实体都调用persist,或者使用cascade persist选项设置关系。您发布的这个示例缺少使其工作所需的一些更精细的详细信息-请参阅rence还有一些。谢谢你的回答。我使用Neils answer,但在同步过程中,通过未标记为cascade PERSIST:entity.NoteBook[noteBookid=null]的关系找到了一个新对象。错误。错误指向em.getTransaction().commit()
这是一个新问题,可能是因为在调用persist之前向关系中添加了一个实体。在设置关系之前,可以对两个实体都调用persist,或者使用cascade persist选项设置关系。您发布的这个示例缺少使其工作所需的一些更精细的详细信息-请参阅还有一些其他的。