一.一对多的关联配置
数据库：主表从表，通过外键关联
类：
class A{
B b；
}
class B{
}
例1:order实体类与orderItem实体类
①order
package com.zy.two.entity;
import java.util.HashSet;
import java.util.Set;
public class Order {
// create table t_hibernate_order
// (
// order_id int primary key auto_increment,
// order_no varchar(50) not null
// );
private Integer orderId;
private String orderNo;
//注意：变量属性一定用接口进行接受
private Set orderItems = new HashSet<>();
private Integer initOrderItems = 0;//0代表懒加载，1代表强制加载
public Integer getInitOrderItems() {
return initOrderItems;
}
public void setInitOrderItems(Integer initOrderItems) {
this.initOrderItems = initOrderItems;
}
public Set getOrderItems() {
return orderItems;
}
public void setOrderItems(Set orderItems) {
this.orderItems = orderItems;
}
public Integer getOrderId() {
return orderId;
}
public void setOrderId(Integer orderId) {
this.orderId = orderId;
}
public String getOrderNo() {
return orderNo;
}
public void setOrderNo(String orderNo) {
this.orderNo = orderNo;
}
}
②.orderItem
package com.zy.two.entity;
public class OrderItem {
// create table t_hibernate_order_item
// (
// order_item_id int primary key auto_increment,
// product_id int not null,
// quantity int not null,
// oid int not null,
// foreign key(oid) references t_hibernate_order(order_id)
// );
private Integer orderItemId;
private Integer productId;
private Integer quantity;
private Integer oid;
private Order order;
public Order getOrder() {
return order;
}
public void setOrder(Order order) {
this.order = order;
}
public Integer getOrderItemId() {
return orderItemId;
}
public void setOrderItemId(Integer orderItemId) {
this.orderItemId = orderItemId;
}
public Integer getProductId() {
return productId;
}
public void setProductId(Integer productId) {
this.productId = productId;
}
public Integer getQuantity() {
return quantity;
}
public void setQuantity(Integer quantity) {
this.quantity = quantity;
}
public Integer getOid() {
return oid;
}
public void setOid(Integer oid) {
this.oid = oid;
}
}
对于一个订单来说，它有多个订单项
所以order实体类中包含订单项集合的属性
而对于订单项表来说，它一定属于某个订单
二.懒加载
