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;
	}
}