hibernate annotation 多对一关联

记录一下annotation代替*.hbm.xml的第一个程序

使用annotation需先导入java ee中的javax.persistence包。我当时只装了java se JDK 所以就抛ClassNotFound异常。

有两个实体product -- category

 

@Entity()
@Table(name="product",catalog="test")
public class Product implements Serializable {
	private Integer id;
	private Category category;
	private String name;
	private String price;
	private String description;
	
	public Product() {
		// TODO Auto-generated constructor stub
	}
	public Product(Category category, String name, String price,
			String description) {
		super();
		this.category = category;
		this.name = name;
		this.price = price;
		this.description = description;
	}
	@GenericGenerator(name="generator",strategy="increment")//按自增策略生产标示符
	@Id
	@GeneratedValue(generator="generator")
	@Column(name="id",nullable=true,length=10)
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	
	@ManyToOne(fetch=FetchType.LAZY)
	@JoinColumn(name="c_id")
	public Category getCategory() {
		return category;
	}
	public void setCategory(Category category) {
		this.category = category;
	}
	
	@Column(name = "name")
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	@Column(name="price",length=10)
	public String getPrice() {
		return price;
	}
	public void setPrice(String price) {
		this.price = price;
	}
	
	@Column(name="description")
	public String getDescription() {
		return description;
	}
	public void setDescription(String descripton) {
		this.description = descripton;
	}
}

 @Entity

 

@Table(name="category",catalog="test")
public class Category implements Serializable {
	private Integer id;
	private String name;
	private String description;
	private Set<Product> products = new HashSet<Product>();
	
	public Category() {
		// TODO Auto-generated constructor stub
	}
	
	public Category(String name, String description, Set<Product> products) {
		super();
		this.name = name;
		this.description = description;
		this.products = products;
	}
	@GenericGenerator(name="generator",strategy="increment")
	@Id
	@GeneratedValue(generator="generator")
	@Column(name="id",unique=true,nullable=false)
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	
	@Column(name="name", length=20)
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	@Column(name="description", length=500)
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}
	//此处只需要注释OneToMany,不需要注释JoinColumn.
        //注释@JoinColumn在多的一端
	@OneToMany(cascade=CascadeType.ALL,mappedBy="category")
	public Set<Product> getProducts() {
		return products;
	}
	public void setProducts(Set<Product> products) {
		this.products = products;
	}

 

hibernate.cfg.xml依然没有变，只是把<mapping resource=""/>换成了<mapping class="">

<hibernate-configuration> 
	<session-factory>		
		<property name="connection.url">
			jdbc:mysql://localhost:3306/test
		</property>
		<property name="connection.username">root</property>
		<property name="connection.password">1234</property>
		<property name="connection.driver_class">
			com.mysql.jdbc.Driver
		</property>
		<property name="dialect">
			org.hibernate.dialect.MySQLDialect
		</property>
		
		<property name="format_sql">true</property>
		<property name="show_sql">true</property>
		<property name="hibernate.id.new_generator_mappings">true</property>
		<property name="current_session_context_class">thread</property>
		<mapping class="entity.Product" />
		<mapping class="entity.Category" />
	</session-factory>
</hibernate-configuration>	

 最后在插入一个工具类吧

public class HibernateUtil {

	private static final SessionFactory sessionFactory;
	static{
		try{
			sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
		} catch (Throwable e){
			throw new  ExceptionInInitializerError(e);
		}
	}	
	public static Session getSession() throws HibernateException{
		return sessionFactory.openSession();
	}
}