Hibernate注解Annotation

大部分仍然使用javax.persistence中的注解，有些Hibernate扩展的注解，在org.hibernate.annotations包中，如GenericGenerator.

使用hibernate.cfg.xml中配置的事务，使用<mapping class="完整类名"/>加载注解的持久化类。Hibernate中可以混合使用注解和xml映射文件。

注解后不能使用Configuration类，而是AnnotationConfiguration类初始化Hibernate

        SessionFactory sFactory=new AnnotationConfiguration()
                              .configure().buildSessionFactory();
        Session session=sFactory.getCurrentSession();
        Transaction tx=session.beginTransaction();
        User user=new User();
        user.setUsername("tazi2");
        user.setPassword("12345");
        session.save(user);
        tx.commit();

注解种类：

@Entity @Table @Id @Column @Transient(非持久化属性) @Temporal(时间精度) @ManyToOne @... 

在类前

@NamedQueries({@NamedQuery(name="getById",query="from User where id=:id")})

使用方法与在xml配置的命名查询相同

        Query query=session.getNamedQuery("getById");
        query.setInteger("id", 4);
        User user=(User)query.uniqueResult();
        System.out.println(user.getUsername());

@Version乐观锁 @Cache二级缓存 @Filters @FilterDef 

@GeneratedValue默认为AUTO,根据底层数据库决定。还可以用Hibernate扩展的@GenericGenerator

例子：

package com.tazi.domin;

import java.sql.Timestamp;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Lob;
import javax.persistence.ManyToOne;

/**
 * Product entity. @author MyEclipse Persistence Tools
 */
@Entity
public class Product implements java.io.Serializable {
    // Fields
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;
    @Column(length=20,nullable=false)
    private String name;
    @Column(scale=2)
    private Float price;
    @Lob
    private String description;
    @ManyToOne
    @JoinColumn(name="CATEGORY_ID")//,referencedColumnName="ID"
    private Category category;  
    // Constructors
    public Category getCategory() {
        return category;
    }

    public void setCategory(Category category) {
        this.category = category;
    }

    //... Property accessors
   }

Category.java

package com.tazi.domin;

import java.util.HashSet;
import java.util.Set;

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;

/**
 * Category entity. @author MyEclipse Persistence Tools
 */
@Entity
public class Category implements java.io.Serializable {

    // Fields
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;
    @Column
    private String name;
    private String description;
    @OneToMany(
        cascade={CascadeType.ALL},
        fetch=FetchType.EAGER, //使用List不能使用eager,使用Set可以
        mappedBy="category"
    )
    private Set<Product> products = new HashSet(0);

    // Constructors

    /** default constructor */
    public Category() {
    }
    /** minimal constructor */
    public Category(String name) {
        this.name = name;
    }
    /** full constructor */
    public Category(String name, String description, Set products) {
        this.name = name;
        this.description = description;
        this.products = products;
    }
    //... Property accessors
}