帮助Hibernate集合外键映射
我遇到了很大的困难，让我的映射文件通过Hibernate中的外键来处理元素的集合。 Java将尝试在下面加载这些文件，并且不会有任何运行时异常，但事件表永远不会作为员工的对象加载（它将保持为空，但从数据库加载其他任何属性）。 在我的MySQL数据库中，我有以下内容：
表：员工
主键：username varchar
名称varchar
areacode INTEGER
电话INTEGER
地址号INTEGER
addressLocation varchar
email varchar
表格：事件
主键：ID INTEGER
startDate DateTime
endDate DateTime
customerName varchar
employeeUsername varchar
<?xml version="1.0"?>
<class name="Employee" table="Employees">
<id name="username" column="username" type="string"/>
<many-to-one name="contact" class="Contact" column="username" unique="false" update="false" insert="false" optimistic-lock="true" not-found="exception" embed-xml="true" />
</class>
<class name="Contact" table="Employees">
<id name="username" column="username" type="string"/>
<property name="name" column="name" type="string"/>
<property name="addressNumber" column="addressNumber" type="int"/>
<property name="areacode" column="areacode" type="int"/>
<property name="phone" column="phone" type="int"/>
<property name="addressLocation" column="addressLocation" type="string"/>
<property name="email" column="email" type="string"/>
</class>
<?xml version="1.0"?>
<class name="Event" table="Events">
<id name="ID" column="ID" type="int">
<generator class="assigned"/>
</id>
<property name="startDate" column="startDate" type="date"/>
<property name="endDate" column="endDate" type="date"/>
<property name="customerName" column="customerName" type="string"/>
</class>
<class name="Employee" table="Events" entity-name="Employee2">
<id name="username" column="employeeUsername" type="string"/>
<list name="events" cascade="all">
<key column="employeeUsername"/>
<list-index column="ID"/>
<one-to-many class="Event"/>
</list>
</class>
假设hibernate.cfg.xml文件存在并且可行（如果您觉得需要显示，请告诉我）。 它确实在其映射文件部分包含了这两个文件。
我有一种感觉，我的错误可能出现在我的“list”声明中的事件集合声明中。 这里是Java类：
package org.hibernate.employee;
import java.util.Date;
公共类Event {private int ID; 私人日期startDate; 私人日期结束日期; 私人字符串customerName;
public Event(){
System.out.println("blah");
}
/**
* @return the iD
*/
public int getID() {
return ID;
}
/**
* @param id the iD to set
*/
public void setID(int id) {
ID = id;
}
/**
* @return the startDate
*/
public Date getStartDate() {
return startDate;
}
/**
* @param startDate the startDate to set
*/
public void setStartDate(Date startDate) {
this.startDate = startDate;
}
/**
* @return the endDate
*/
public Date getEndDate() {
return endDate;
}
/**
* @param endDate the endDate to set
*/
public void setEndDate(Date endDate) {
this.endDate = endDate;
}
/**
* @return the customerName
*/
public String getCustomerName() {
return customerName;
}
/**
* @param customerName the customerName to set
*/
public void setCustomerName(String customerName) {
this.customerName = customerName;
}
}
/*
*文件：Contact.java * /
包org.hibernate.employee;
/ ** *此类表示员工的联系信息。 * * / public class Contact {
private int username; // the contact identifier in the database
private int areacode; // the contact areacode
private int phone; // the contact phone
private String name; // the contact's name
private int addressNumber; // the contact's address number
private String addressLocation; // the contact's address location
private String email; // the contact's email
/**
* Constructs a Contact object.
*/
public Contact() {
}
/**
* @return the areacode
*/
public int getAreacode() {
return areacode;
}
/**
* @param areacode the areacode to set
*/
public void setAreacode(int areacode) {
this.areacode = areacode;
}
/**
* @return the phone
*/
public int getPhone() {
return phone;
}
/**
* @param phone the phone to set
*/
public void setPhone(int phone) {
this.phone = phone;
}
/**
* @return the name
*/
public String getName() {
return name;
}
/**
* @param name the name to set
*/
public void setName(String name) {
this.name = name;
}
/**
* @return the addressNumber
*/
public int getAddressNumber() {
return addressNumber;
}
/**
* @param addressNumber the addressNumber to set
*/
public void setAddressNumber(int addressNumber) {
this.addressNumber = addressNumber;
}
/**
* @return the addressLocation
*/
public String getAddressLocation() {
return addressLocation;
}
/**
* @param addressLocation the addressLocation to set
*/
public void setAddressLocation(String addressLocation) {
this.addressLocation = addressLocation;
}
/**
* @return the email
*/
public String getEmail() {
return email;
}
/**
* @param email the email to set
*/
public void setEmail(String email) {
this.email = email;
}
public String toString(){
String retVal = "";
retVal += "Address: " + this.addressNumber + " " + this.addressLocation + "n";
retVal += "Email: " + this.email + "n";
retVal += "Phone: " + this.areacode + " " + this.phone + "n";
retVal += "Name: " + this.name + "n";
return retVal;
}
public void setUsername(int username) {
this.username = username;
}
public int getUsername() {
return username;
}
}
/*
*文件：Employee.java * /
包org.hibernate.employee; import java.util.List;
/ ** *此类表示公司数据库中的员工。 * * / public class Employee {
private String username; // the employee's username
private Contact contact; // the employee's contact information
private List events;
/**
* Constructs an Employee object.
*/
public Employee() {
super();
}
/**
* @return the username
*/
public String getUsername() {
return username;
}
/**
* @param username the username to set
*/
public void setUsername(String username) {
this.username = username;
}
/**
* @return the contact
*/
public Contact getContact() {
return contact;
}
/**
* @param contact the contact to set
*/
public void setContact(Contact contact) {
this.contact = contact;
}
/**
* @return the events
*/
public List getEvents() {
return events;
}
/**
* @param events the events to set
*/
public void setEvents(List events) {
this.events = events;
}
public String toString(){
String retVal = "";
System.out.println(events);
retVal += "Username: " + username + "n";
retVal += "Contact: " + contact + "n";
return retVal;
}
}
您的映射出于两个（主要）原因是错误的：
many-to-one需要一个外键（例如一个单独的列）; 您正在尝试重新使用主键。 你应该做的是：
Contact作为组件。 Employee上将事件集合映射为一对多关联。 就像是：
<class name="Employee" table="Employees">
<id name="username" column="username" type="string"/>
<component name="Contact" class="Contact"> <!-- class attribute optional -->
<property name="name" column="name" type="string"/>
<property name="addressNumber" column="addressNumber" type="int"/>
<property name="areacode" column="areacode" type="int"/>
<property name="phone" column="phone" type="int"/>
<property name="addressLocation" column="addressLocation" type="string"/>
<property name="email" column="email" type="string"/>
</component>
<list name="events" cascade="all">
<key column="employeeUsername"/>
<list-index column="event_idx"/>
<one-to-many class="Event"/>
</list>
</class>
请注意，如果要将事件列表映射为有序列表，则list-index应该真的是表中的单独列; 你不能将它映射到id。 如果不希望把它定义为一个柱，既可以映射列表作为<bag>代替（和，可选地，指定order-by属性进行排序该袋通过）或它映射为复合元件的集合，其中每个事件将不再是一个独立的实体。 这是否适用取决于您的业务要求。