JPA入门（二）双向一对多

package org.jzkangta.onetomany;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;/** * 多的一方为关系维护端，关系维护端是指负责外键的更新 * @author Administrator * */@Entitypublic class OrderItem {@Id@GeneratedValueprivate int id;@Column(length=40,nullable=false)private String name;@Column(nullable=false)private Float price = 0f;@ManyToOne(cascade={CascadeType.MERGE,CascadeType.REFRESH},fetch=FetchType.EAGER,optional=false)//cascade不用为ALL，fetch=FetchType.EAGER为默认，optional=true是指order可以为null@JoinColumn(name="order_id")//外键的字段名字private Order order;public int getId() {    return id;    }public void setId( int id ) {    this.id = id;    }public String getName() {    return name;    }public void setName( String name ) {    this.name = name;    }public Float getPrice() {    return price;    }public void setPrice( Float price ) {    this.price = price;    }public Order getOrder() {    return order;    }public void setOrder( Order order ) {    this.order = order;    }}