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;
}
}