Hibernate的注解

以Hibernate3.3作为例子。

一、常用的注解

1.@Entity(name = "entityName")：

必须，name为可选，对应数据库中一的个表

2.@Table(name = "", catalog = "", schema = "") ：

可选，通常和@Entity配合使用，只能标注在实体的class定义处，表示实体对应的数据库表的信息
name：可选，表示表的名称。默认表名和实体名称一致，只有在不一致的情况下才需要指定表名

catalog：可选，表示Catalog名称，默认为Catalog("")
schema：可选，表示Schema名称，默认为Schema("")

3.@Id

必须

@Id定义了映射到数据库表的主键的属性,一个实体只能有一个属性被映射为主键，置于getXxxx()上

4.@GeneratedValue(strategy = GenerationType, generator = "")

可选

strategy：表示主键生成策略，有AUTO，INDENTITY，SEQUENCE 和 TABLE 4种，分别表示让ORM框架自动选择，根据数据库的Identity字段生成，根据数据库表的Sequence字段生成，以有根据一个额外的表生成主键，默认为AUTO

generator：表示主键生成器的名称，这个属性通常和ORM框架相关，例如Hibernate可以指定uuid等主键生成方式

5.@Basic(fetch = FetchType, optional = true)

可选

@Basic表示一个简单的属性到数据库表的字段的映射，对于没有任何标注的getXxxx()方法，默认即为@Basic
fetch：表示该属性的读取策略，有EAGER和LAZY两种，分别表示主支抓取和延迟加载，默认为EAGER
optional：表示该属性是否允许为null，默认为true

6.@Column(name = "", unique = true, nullable = false, precision = 9, scale = 0)

可选

@Column描述了数据库表中该字段的详细定义，这对于根据JPA注解生成数据库表结构的工具非常有作用
name：表示数据库表中该字段的名称，默认情形属性名称一致
nullable：表示该字段是否允许为null，默认为true
unique：表示该字段是否是唯一标识，默认为false
length：表示该字段的大小，仅对String类型的字段有效
insertable：表示在ORM框架执行插入操作时，该字段是否应出现INSETRT语句中，默认为true
updateable：表示在ORM框架执行更新操作时，该字段是否应该出现在UPDATE语句中，默认为true。对于一经创建就不可以更改的字段，该属性非常有用，如对于birthday字段
columnDefinition：表示该字段在数据库中的实际类型.通常ORM框架可以根据属性类型自动判断数据库中字段的类型，但是对于Date类型仍无法确定数据库中字段类型究竟是DATE，TIME还是TIMESTAMP。此外，String的默认映射类型为VARCHAR，如果要将String类型映射到特定数据库的BLOB或TEXT字段类型，该属性非常有用

7.@Transient

可选

@Transient表示该属性并非一个到数据库表的字段的映射，ORM框架将忽略该属性。如果一个属性并非数据库表的字段映射，就务必将其标示为@Transient，否则，ORM框架默认其注解为@Basic

8.@ManyToOne(fetch = FetchType, cascade = CascadeType) 

可选

@ManyToOne表示一个多对一的映射，该注解标注的属性通常是数据库表的外键
optional：是否允许该字段为null，该属性应该根据数据库表的外键约束来确定，默认为true
fetch：表示抓取策略，默认为FetchType.EAGER
cascade：表示默认的级联操作策略，可以指定为ALL、PERSIST、MERGE、REFRESH和REMOVE中的若干组合，默认为无级联操作
targetEntity：表示该属性关联的实体类型，该属性通常不必指定，ORM框架根据属性类型自动判断targetEntity

9.@JoinColumn

可选

@JoinColumn和@Column类似，介量描述的不是一个简单字段，而一一个关联字段，例如，描述一个@ManyToOne的字段
name：该字段的名称。由于@JoinColumn描述的是一个关联字段，如ManyToOne，则默认的名称由其关联的实体决定

10.@OneToMany(fetch = FetchType, cascade = CascadeType) 

可选

@OneToMany描述一个一对多的关联，该属性应该为集体类型，在数据库中并没有实际字段
fetch：表示抓取策略，默认为FetchType.LAZY，因为关联的多个对象通常不必从数据库预先读取到内存
cascade：表示级联操作策略，对于OneToMany类型的关联非常重要，通常该实体更新或删除时，其关联的实体也应当被更新或删除

11.@OneToOne(fetch = FetchType, cascade = CascadeType) 

可选

@OneToOne描述一个一对一的关联
fetch：表示抓取策略,默认为FetchType.LAZY
cascade：表示级联操作策略

12.@ManyToMany

可选

@ManyToMany描述一个多对多的关联，多对多关联上是两个一对多关联，但是在ManyToMany描述中，中间表是由ORM框架自动处理
targetEntity：表示多对多关联的另一个实体类的全名，例如：package.Book.class
mappedBy：表示多对多关联的另一个实体类的对应集合属性名称

13.@MappedSuperclass

可选
@MappedSuperclass可以将超类的JPA注解传递给子类，使子类能够继承超类的JPA注解

14.@Embedded

可选
@Embedded将几个字段组合成一个类，并作为整个Entity的一个属性

二、新建一Java Project，并搭建Hibernate3.3框架

 1.必须打勾，支持Hibernate的注解

2.打不打勾都行

三、映射两个实体类：

Employee类：

package org.e276.entity;

import java.util.Date;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

/**
 * Employee entity. @author MyEclipse Persistence Tools
 */
@Entity
@Table(name = "EMPLOYEE", schema = "Y2")
public class Employee implements java.io.Serializable {

	// Fields

	private Integer id;
	private Department department;
	private String name;
	private Boolean sex;
	private Double salary;
	private Date birthday;

	// Constructors

	/** default constructor */
	public Employee() {
	}

	/** minimal constructor */
	public Employee(Integer id) {
		this.id = id;
	}

	/** full constructor */
	public Employee(Integer id, Department department, String name, Boolean sex, Double salary,
			Date birthday) {
		this.id = id;
		this.department = department;
		this.name = name;
		this.sex = sex;
		this.salary = salary;
		this.birthday = birthday;
	}

	// Property accessors
	@Id
	@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generator")
	@SequenceGenerator(name = "generator", sequenceName = "emp_seq")
	@Column(name = "ID", unique = true, nullable = false, precision = 9, scale = 0)
	public Integer getId() {
		return this.id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	@ManyToOne(fetch = FetchType.EAGER)
	@JoinColumn(name = "DEPART_ID")
	public Department getDepartment() {
		return this.department;
	}

	public void setDepartment(Department department) {
		this.department = department;
	}

	@Column(name = "NAME", length = 20)
	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Column(name = "SEX", precision = 1, scale = 0)
	public Boolean getSex() {
		return this.sex;
	}

	public void setSex(Boolean sex) {
		this.sex = sex;
	}

	@Column(name = "SALARY", precision = 8)
	public Double getSalary() {
		return this.salary;
	}

	public void setSalary(Double salary) {
		this.salary = salary;
	}

	@Temporal(TemporalType.DATE)
	@Column(name = "BIRTHDAY", length = 7)
	public Date getBirthday() {
		return this.birthday;
	}

	public void setBirthday(Date birthday) {
		this.birthday = birthday;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", department=" + department + ", name=" + name + ", sex="
				+ sex + ", salary=" + salary + ", birthday=" + birthday + "]";
	}
	
}

Department类：

package org.e276.entity;

import java.util.ArrayList;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.OrderBy;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
import org.hibernate.annotations.Formula;

/**
 * Department entity. @author MyEclipse Persistence Tools
 */
@Entity
@Table(name = "DEPARTMENT", schema = "Y2")
public class Department implements java.io.Serializable {

	// Fields

	private Integer id;
	private Integer count;//作为只读属性，表中没有这列
	private String name;
	private List<Employee> employees = new ArrayList<Employee>(0);

	// Constructors

	/** default constructor */
	public Department() {
	}

	/** minimal constructor */
	public Department(Integer id, String name) {
		this.id = id;
		this.name = name;
	}

	/** full constructor */
	public Department(Integer id, String name, List<Employee> employees) {
		this.id = id;
		this.name = name;
		this.employees = employees;
	}

	// Property accessors
	@Id
	@GeneratedValue(strategy=GenerationType.SEQUENCE,generator="generator")
	@SequenceGenerator(name="generator",sequenceName="depart_seq")
	@Column(name = "ID", unique = true, nullable = false, precision = 4, scale = 0)
	public Integer getId() {
		return this.id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	@Column(name = "NAME", nullable = false, length = 20)
	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "department")
	@OrderBy("salary desc")
	public List<Employee> getEmployees() {
		return this.employees;
	}

	public void setEmployees(List<Employee> employees) {
		this.employees = employees;
	}

	//注意前后一定要有括号，查询时是作为一列存在的子查询
	@Formula("(select count(*) from department)")
	public Integer getCount() {
		return count;
	}

	public void setCount(Integer count) {
		this.count = count;
	}

}

七、Hibernate的配置文件

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>

<session-factory>
	<property name="dialect">
		org.hibernate.dialect.Oracle10gDialect
	</property>
	<property name="connection.url">
		jdbc:oracle:thin:@localhost:1521:orcl
	</property>
	<property name="connection.username">y2</property>
	<property name="connection.password">bdqn</property>
	<property name="connection.driver_class">
		oracle.jdbc.driver.OracleDriver
	</property>
	<property name="myeclipse.connection.profile">Y2</property>
	<property name="show_sql">true</property>
	<property name="format_sql">true</property>
	<mapping class="org.e276.entity.Department" />
	<mapping class="org.e276.entity.Employee" />

</session-factory>

</hibernate-configuration>

八、测试类（使用了Junit 4.0）：

package org.e276.test;

import java.util.Date;
import java.util.List;
import org.e276.entity.Department;
import org.e276.entity.Employee;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.AnnotationConfiguration;
import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;

/**
 * 测试类
 * 
 * @author miao
 * 
 */
public class TestEmployee {

	static SessionFactory factory = null;
	private Session session;
	private Transaction tx;

	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
		factory = new AnnotationConfiguration().configure("hibernate.cfg.xml")
				.buildSessionFactory();
	}

	@AfterClass
	public static void tearDownAfterClass() throws Exception {
		factory = null;
	}

	@Before
	public void setUp() throws Exception {
		session = factory.openSession();
		tx = session.beginTransaction();
	}

	@After
	public void tearDown() throws Exception {
		tx.commit();
		session.close();
	}

	/**
	 * 查询部门的信息 部门名字 部门总数 员工数
	 */
	public void findDepartInfo() {
		Department department = (Department) session.get(Department.class, 3);
		// 得到部门名字
		System.out.println("部门名字是：" + department.getName());
		// 输出部门总数
		System.out.println("部门总数是：" + department.getCount());
		// 得到员工集合
		List<Employee> employees = department.getEmployees();
		// 输出员工，按工资降序排列
		for (Employee employee : employees) {
			System.out.println(employee);
		}
	}

	/**
	 * 查询所有的员工
	 */
	@Test
	public void findAllEmployee() {
		@SuppressWarnings("unchecked")
		List<Employee> employees = session.createQuery("from Employee").list();
		for (Employee employee : employees) {
			System.out.println(employee);
		}
	}

	/**
	 * 插入员工信息
	 */
	public void addEmployee() {
		Department department = (Department) session.get(Department.class, 3);
		Employee employee = new Employee();
		employee.setDepartment(department);
		employee.setName("小伙伴");
		employee.setSex(false);
		employee.setBirthday(new Date());
		employee.setSalary(3800.00);
		try {
			// 保存
			session.save(employee);
			System.out.println("添加成功！");
		} catch (HibernateException e) {
			System.out.println("添加失败！");
			e.printStackTrace();
		}
	}
}