【MyBatis】Mybatis中EL表定式总结

【MyBatis】Mybatis中EL表定式总结

Mybatis是使用OGNL表达式来解析的，关于OGNL详细信息请查看官网:https://commons.apache.org/proper/commons-ognl/language-guide.html

一、字符串相关

1）null 判断

	and book_name is null



	and book_name is not null

2）判断字符串不等于空串

	and book_name = ''



	and book_name = ''

3）单字符问题

	and book_name = '1'

上面代码，在 bookname等于1，不成立，这是由于OGNL的表达式中，'1' 会被解析成字符，java是强类型的，char 和 一个string 不是同一种类型。

正确写法如下：

	and book_name = '1'



	and book_name = '1'

4）自身方法调用

EL表示式可以直接调用自身方法

	and book_name = #{bookname}


	and book_name = #{bookname}


	and book_name = #{bookname}

5）字符串转数组

EL字符串，调用split方法，转换成数组。

    
        #{item}
    


    
        #{item}
    

注：

在字符串比较中：

二、数字类型

1）普通判断

	and id = #{id}


	and id = #{id}

2）0值问题

	and id = 0

Interpreting Objects as Booleans

Any object can be used where a boolean is required. OGNL interprets objects as booleans like this:

• If the object is a Boolean, its value is extracted and returned;
• 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;
• If the object is a Character, its boolean value is true if and only if its char value is non-zero;
• Otherwise, its boolean value is true if and only if it is non-null.

在数字类型与非数字类型比较时，数值0或者浮点数字0.00被解析成false,同理，空串''也被解析成false。

具体用例如下：id等于0的情况下：

	and id = 0



    and id = 2



    and id = 3



    and id = 4



    and id = 5

三、调用静态函数

EL表达式可以直接调用Java中静态类，表达式：@class@method

	
		select * from book
		
			
				and 1 = 1
			
			
				and 1 = 2
			
		
	

代码地址：https://gitee.com/firefish/mybatis_study