第十章 基于Annotation的关系映射 多对一与一对多

如果下面部分内容有不明白的可以查找：

基于Annotation的关系映射 前期准备:http://blog.csdn.net/p_3er/article/details/9061911

基于xml的多对一:http://blog.csdn.net/p_3er/article/details/9036759

基于xml的一对多:http://blog.csdn.net/p_3er/article/details/9036921

本文是把多对一与一对多结合起来了，形成一个双向的映射。如果只想要单向的话，把别外一边的注解去掉就是了。

Department:

@Entity@Table(name = "department", catalog = "hibernate")public class Department implements java.io.Serializable {private Integer id;private String name;private Set<Employee> employees = new HashSet<Employee>(0);public Department() {}public Department(String name, Set<Employee> employees) {this.name = name;this.employees = employees;}@Id@GeneratedValue@Column(name = "id", unique = true, nullable = false)public Integer getId() {return this.id;}public void setId(Integer id) {this.id = id;}@Column(name = "name", nullable = false, length = 45)public String getName() {return this.name;}public void setName(String name) {this.name = name;}@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "department")/*一对多。department和employee的一对多关系中,当指定department中的mappedBy后,关系只能被employee来主动维护.也就是employee级联的处理department.          之前的映射文件：         <set name="employees" inverse="false" cascade="all"><key column="department_id"></key><one-to-many class="cn.framelife.hibernate.entity.Employee"/></set>*/public Set<Employee> getEmployees() {return this.employees;}public void setEmployees(Set<Employee> employees) {this.employees = employees;}}

Employee:

@Entity@Table(name = "employee", catalog = "hibernate")public class Employee implements java.io.Serializable {private Integer id;private Department department;private String name;public Employee() {}@Id@GeneratedValue@Column(name = "id", unique = true, nullable = false)public Integer getId() {return this.id;}public void setId(Integer id) {this.id = id;}@ManyToOne(fetch = FetchType.LAZY)@JoinColumn(name = "department_id")/*多对一。     <many-to-one name="department" column="department_id"></many-to-one>*/public Department getDepartment() {return this.department;}public void setDepartment(Department department) {this.department = department;}@Column(name = "name", nullable = false, length = 45)public String getName() {return this.name;}public void setName(String name) {this.name = name;}}