mybatis 標簽０為null 無效的 踩坑

 

采過一個坑，寫篇日志來記錄下

<if test="orderStatus != null and orderStatus !=''">
 and t.is_ship=#{orderStatus}
</if>

 

當狀態值設置為０時，操作完了，數據庫沒反應，沒有設置為０ 
把狀態用1和2表示，不使用０，一切正常，問題消失了。 

MyBatis的表達式是用OGNL處理的。OGNL表達式的規則如下

1. Interpreting Objects as Booleans
2. Any object can be used where a boolean is required. OGNL interprets objects as booleans like this:
3.  
4. If the object is a Boolean, its value is extracted and returned;
5.  
6. If the object is a Number, its double-precision floating-point value is compared with zero; non-zero is treated as true, zero as false;
7.  
8. If the object is a Character, its boolean value is true if and only if its char value is non-zero;
9.  
10. Otherwise, its boolean value is true if and only if it is non-null.

 

根據這一條If the object is a Number, its double-precision floating-point value is compared with zero; non-zero is treated as true, zero as false

　 

state !='' 　傳入０時，表達式的值為false;所以不執行。 
解決辦法，把這個刪掉就可以了。

<if test="state != null">state = #{state }</if>

<if test="orderStatus != null ">
 and t.is_ship=#{orderStatus}
</if>

本來只有String類型的才會進行這樣的判斷——xx!= ''，其實是自己碼代碼時只顧自制粘貼，自己給自己埋了個坑。

這里有必要再提一個“坑”，如果類似於String str =”A”; 這樣的寫法時時，根據第三條規則，OGNL將會識別為Java 中的 char類型，顯然String 類型與char類型做==運算會返回false，從而導致表達式不成立。解決方法很簡單，修改為

<if test='str!= null and str == "A"'>