关于JPA一对一关系的删除问题,有请大家帮忙,感激不尽

我的问题是,给人员分配一个登录帐号,一个人员可以用一个帐号或者没有.现在我给一个人员分配了一个登录帐号,我想把他的帐号删除掉,出现异常.
person.java

@Entity
public class Person implements Serializable{

	// id
	private int id;
	// 人员名称
	private String name;
	//对应用户
	private User user;
	@OneToOne(mappedBy="person",cascade={CascadeType.ALL})
	public User getUser() {
		return user;
	}

	public void setUser(User user) {
		this.user = user;
	}
	....(set,get方法)
}

User.java

@Entity
public class User implements Serializable{
	private int id;
	// 帐号
	private String username;
	// 密码
	// 对应人员
	private Person person;

	@OneToOne(targetEntity = Person.class, cascade ={CascadeType.PERSIST,CascadeType.PERSIST,CascadeType.MERGE},optional=false)
	@JoinColumn(unique = true)
	public Person getPerson() {
		return person;
	}
        ....(SET,GET方法)
}

UserAction.java的删除方法如下

public String del() throws Exception {
		User user = userService.find(id);
		userService.delete(id);
		return "pub_del_success";
	}

删除出现的异常如下:
Stacktraces
org.springframework.transaction.TransactionSystemException:
Could not commit JPA transaction;
nested exception is javax.persistence.RollbackException:
Error while commiting the transaction