mybatis <if test=""></if>标签０为null 无效的 踩坑

采过一个坑，写篇日志来记录下

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

当状态值设置为０时，操作完了，数据库没反应，没有设置为０ 
把状态用1和2表示，不使用０，一切正常，问题消失了。 

MyBatis的表达式是用OGNL处理的。OGNL表达式的规则如下

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.

根据这一条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 !='' 　传入０时，表达式的值为false;所以不执行。 
解决办法，把这个删掉就可以了。

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

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

本来只有String类型的才会进行这样的判断——xx!= ''，其实是自己码代码时只顾自制粘贴，自己给自己埋了个坑。

这里有必要再提一个“坑”，如果类似于String str =”A”; 这样的写法时时，根据第三条规则，OGNL将会识别为Java 中的 char类型，显然String 类型与char类型做==运算会返回false，从而导致表达式不成立。解决方法很简单，修改为

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