jpa 双向一对多，多对一关联关系

1.1.  双向一对多

Order.java

package com.morris.entity; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.Id; import javax.persistence.OneToMany; import javax.persistence.Table; @Entity @Table(name="orders") public class Order { @Id @Column(name="order_id",length=32) private String orderId; @Column(name="order_name",length=50) private String orderName; /** * OneToMany:一对多的配置 * mappedBy="order":指定由多的一方的order属性维护关联关系 * */ @OneToMany(cascade={CascadeType.REFRESH,CascadeType.MERGE,CascadeType.REMOVE,CascadeType.PERSIST},fetch=FetchType.LAZY,mappedBy="order") private Set<OrderItem> orderItems; public Order(String orderId, String orderName, Set<OrderItem> orderItems) { super(); this.orderId = orderId; this.orderName = orderName; this.orderItems = orderItems; } public Set<OrderItem> getOrderItems() { return orderItems; } public void setOrderItems(Set<OrderItem> orderItems) { this.orderItems = orderItems; } public Order() { super(); // TODO Auto-generated constructor stub } public Order(String orderId, String orderName) { super(); this.orderId = orderId; this.orderName = orderName; } @Override public String toString() { return "Order [orderId=" + orderId + ", orderName=" + orderName + "]"; } public String getOrderId() { return orderId; } public void setOrderId(String orderId) { this.orderId = orderId; } public String getOrderName() { return orderName; } public void setOrderName(String orderName) { this.orderName = orderName; } }

1.2.  双向多对一

OrderItem.java

package com.morris.entity; 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; import javax.persistence.Table; @Entity @Table(name="order_item") public class OrderItem { @Id @GeneratedValue @Column(name="order_item_id") private Integer orderItemId; @Column(name="product_name",length=50,nullable=false) private String productName; @Column(name="product_price",nullable=false) private Double productPrice; /** * ManyToOne：多对一的配置 * cascade(级联)：all(所有)，merge(更新)，refresh(查询)，persistence(保存)，remove(删除) * fetch: eager:立即加载 one的一方默认是立即加载 * lazy:懒加载 many的一方默认是懒加载 * optional:是否可选,外键是否允许为空 * * JoinColumn:指定外键名 * */ @ManyToOne(cascade={CascadeType.MERGE,CascadeType.REFRESH},fetch=FetchType.EAGER,optional=false) @JoinColumn(name="order_id") private Order order; public OrderItem() { super(); // TODO Auto-generated constructor stub } @Override public String toString() { return "OrderItem [orderItemId=" + orderItemId + ", productName=" + productName + ", productPrice=" + productPrice + ", order=" + order + "]"; } public Integer getOrderItemId() { return orderItemId; } public void setOrderItemId(Integer orderItemId) { this.orderItemId = orderItemId; } public String getProductName() { return productName; } public void setProductName(String productName) { this.productName = productName; } public Double getProductPrice() { return productPrice; } public void setProductPrice(Double productPrice) { this.productPrice = productPrice; } public Order getOrder() { return order; } public void setOrder(Order order) { this.order = order; } public OrderItem(String productName, Double productPrice) { super(); this.productName = productName; this.productPrice = productPrice; } }

1.3.  测试

One2ManyTest.java

package com.morris.test; import java.util.HashSet; import java.util.Set; import java.util.UUID; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; import org.junit.AfterClass; import org.junit.BeforeClass; import org.junit.Test; import com.morris.entity.Order; import com.morris.entity.OrderItem; public class One2ManyTest { private static EntityManagerFactory factory; private static EntityManager manager; @BeforeClass public static void setUpBeforeClass() throws Exception { factory = Persistence.createEntityManagerFactory("jpaDemo"); manager = factory.createEntityManager(); manager.getTransaction().begin(); } @Test public void test() { Order order = new Order(UUID.randomUUID().toString(), "体育商品订单"); OrderItem orderItem1 = new OrderItem("足球",120.0); OrderItem orderItem2 = new OrderItem("篮球",66.0); OrderItem orderItem3 = new OrderItem("羽毛球",118.0); //一定要设置这个,因为orderItem负责维护关联关系 orderItem1.setOrder(order); orderItem2.setOrder(order); orderItem3.setOrder(order); Set<OrderItem> set = new HashSet<>(); set.add(orderItem1); set.add(orderItem2); set.add(orderItem3); order.setOrderItems(set); manager.persist(order); } @AfterClass public static void setUpAfterClass() throws Exception { manager.getTransaction().commit(); manager.close(); factory.close(); } }