雙向一對一映射@OneToOne

雙向一對一的實例我已經上傳到GitHub，entrance項目上了，感興趣的可以下載下來跑跑，這里講兩個在運行過程中遇到的問題。

問題一：上一篇博客的最后我留下了問題。一對一關聯查詢注解@OneToOne的實例詳解

問題點：文章的最后，單向一對一程序在執行save語句的時候，分別執行了下面的語句：

Hibernate: select person0_.id as id1_2_1_, person0_.name as name2_2_1_, person0_.pet_id as pet_id3_2_1_, pet1_.id as id1_3_0_, pet1_.pet_class as pet_clas2_3_0_, pet1_.pet_name as pet_name3_3_0_ from person person0_ inner join pet pet1_ on person0_.pet_id=pet1_.id where person0_.id=?
Hibernate: insert into pet (pet_class, pet_name) values (?, ?)
Hibernate: insert into person (name, pet_id) values (?, ?)
Hibernate: insert into pet (pet_class, pet_name) values (?, ?)
Hibernate: update person set name=?, pet_id=? where id=?

這里我感覺很奇怪的地方就是執行了內連接，所以導致都沒有查到。

再看看雙向一對一執行的語句：

Hibernate: select husband0_.hid as hid1_1_1_, husband0_.hid_card as hid_card2_1_1_, husband0_.hname as hname3_1_1_, husband0_.w_id as w_id4_1_1_, wife1_.wid as wid1_6_0_, wife1_.wid_card as wid_card2_6_0_, wife1_.wname as wname3_6_0_ from husband husband0_ left outer join wife wife1_ on husband0_.w_id=wife1_.wid where husband0_.hid=?
Hibernate: insert into wife (wid_card, wname) values (?, ?)
Hibernate: insert into wife (wid_card, wname) values (?, ?)
Hibernate: update husband set hid_card=?, hname=?, w_id=? where hid=?
Hibernate: update husband set hid_card=?, hname=?, w_id=? where hid=?

雙向一對一連接的話第一句執行的是左連接，所以能查到數據，這樣就能直接更新了。

問題二：異常：在使用fastJson作為工具，將數據庫查到的數據轉換成fastJson輸出，拋出了：java.lang.StackOverflowError: null

這個異常就是堆棧溢出，可以很明顯的看出來，是因為husband對象與wife之前嵌套，在序列化的時候出現了這個異常。網上搜了一些，大多是List集合的嵌套，從中找到些蛛絲馬跡。解決的方法：

方法一：把wife中husband的屬性不序列化，加上屬性transient,加上序列屬性serialVersionUID

	private static final long serialVersionUID = 8091602122698339709L;
	@Id
	// id自動生成
	@GeneratedValue
	@Column(name = "wid")
	private Long wid;
	@Column(name = "wname")
	private String wname;
	@Column(name = "wid_card")
	private String widCard;
	
	 @OneToOne(mappedBy = "wife",cascade=CascadeType.ALL)
	 @JsonBackReference
	 private transient Husband husband;

方法二：重新字節寫toString方法，不要使用系統自己生成的（這里也有技巧）。

husband.toString()

@Override
	public String toString() {
		return "{\"hid\":\"" + hid + "\",\"hname\":\"" + hname
				+ "\",\"hidCard\":\"" + hidCard + "\",\"wife\":" + wife
				+ "} ";
	}

wife.toString()

@Override
	public String toString() {
		return "{\"wid\":\"" + wid + "\",\"wname\":\"" + wname
				+ "\",\"widCard\":\"" + widCard + "\"} ";
	}
	

我的代碼中采用了第二種方法。