JPA单向一对多关联关系@OneToMany

package com.jpa.helloworld;

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.OneToMany;
import javax.persistence.Table;
import javax.persistence.TableGenerator;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.Transient;

import org.hibernate.annotations.Type;
import org.joda.time.DateTime;
import org.joda.time.LocalDate;

@Table(name = "JPA_CUSTOMER")
@Entity
public class Customer {

	private Integer id;

	private String name;

	private String email;

	private int age;

	private Date birth;

	private Set orders = new HashSet<>();

	private DateTime createDate;

	private LocalDate lastUpdateDate;

	private String tran;

	@TableGenerator(name = "ID_GENDERATOR", pkColumnName = "PK_NAME", pkColumnValue = "CUSTOMER_ID", valueColumnName = "PK_VALUE", allocationSize = 5)
	@GeneratedValue(strategy = GenerationType.TABLE, generator = "ID_GENDERATOR")
	@Id
	@Column(name = "C_ID")
	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	@JoinColumn(name = "CUSTOMER_ID")
	@OneToMany(cascade={CascadeType.REMOVE})
	public Set getOrders() {
		return orders;
	}

	public void setOrders(Set orders) {
		this.orders = orders;
	}

	@Column(name = "LAST_NAME", unique = true, length = 20, nullable = false)
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Column(name = "EMAIL", length = 50)
	public String getEmail() {
		return email;
	}

	public void setEmail(String email) {
		this.email = email;
	}

	@Column(name = "AGE", length = 3)
	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	@Transient
	public String getTran() {
		return tran;
	}

	public void setTran(String tran) {
		this.tran = tran;
	}

	@Column(name = "BIRTH")
	@Temporal(TemporalType.DATE)
	public Date getBirth() {
		return birth;
	}

	public void setBirth(Date birth) {
		this.birth = birth;
	}

	@Column(name = "CREATEDATE")
	@Type(type = "org.jadira.usertype.dateandtime.joda.PersistentDateTime")
	public DateTime getCreateDate() {
		return createDate;
	}

	public void setCreateDate(DateTime createDate) {
		this.createDate = createDate;
	}

	@Column(name = "LASTUPDATEDATE")
	@Type(type = "org.jadira.usertype.dateandtime.joda.PersistentLocalDate")
	public LocalDate getLastUpdateDate() {
		return lastUpdateDate;
	}

	public void setLastUpdateDate(LocalDate lastUpdateDate) {
		this.lastUpdateDate = lastUpdateDate;
	}
}

主要关注的是代码中有颜色的地方

接下来说一下关于单项一对多的插入和删除操作

插入

不管先插入多大一端还是一的一端，最终打印的sql语句数量是一样的，因为是由一的一端维护关联关系，所以在插入多的一端时它并不会保存外键值，只有在持久化之后再另外发送update语句更新多的一端的外键值

	@Test
	public void testOnToMany() {
		
		Order o1 = new Order();
		Order o2 = new Order();
		o1.setoName("O-BB");
		o2.setoName("O-CC");
		
		Customer customer = new Customer();
		customer.setName("C-BB");
		customer.setAge(23);
		customer.setBirth(new Date());
		customer.setEmail("[email protected]");
		customer.setCreateDate(DateTime.now());
		customer.setLastUpdateDate(LocalDate.now());
		customer.getOrders().add(o1);
		customer.getOrders().add(o2);
		
		em.persist(customer);
		em.persist(o1);
		em.persist(o2);
		
	}
	

删除

多的一端可以随意删除，主要说一下一的一端

在单向多对一的时候一的一端是不可以删除的

而单项一对多的不同，可以删除一的一端，那么多的一端会被怎么操作呢？根据发出的sql语句可以看出，在默认情况下，删除一的一端，多的一端的外键会被置为null。那么接下来就说一下怎么设置对多的一端的操作。

在@OneToMany注解中有一个cascade属性，它的值是一个CascadeType类的数组

@JoinColumn(name = "CUSTOMER_ID")
@OneToMany(cascade={CascadeType.REMOVE})
public Set getOrders() {
	return orders;
}

ALL 

级联所有实体状态转换

PERSIST 
级联实体持久化操作。

MERGE 
级联实体合并操作。

REMOVE 
级联实体删除操作。

REFRESH 
级联实体刷新操作。

DETACH 
级联实体分离操作。