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Mybatis————动态SQl查询问题

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Mybatis————动态SQl查询问题

今天学习Mybatis框架时，动态SQL查询报如下异常：

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org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'net.zzqd.mybatis.mapper.UserMapper.selectStateUserName'.  It's likely that neither a Result Type nor a Result Map was specified.

经过万能的百度，了解到原来是mapper.xml里没加parameterType和resultType属性，前面的语句没加这两个属性也能执行，暂时不知道是为什么。

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	异常代码
	<!--     动态sql -->
	<select id="selectStateUserName" >
			select * from user 
			where state=1
		<if test="value !=null and value != ''">
		 	AND name like '%${value}%'
		</if> 
		
<!-- 		<if test="value !=null and value != ''"> -->
<!-- 		 	AND name like #{name} -->
<!-- 		</if>  -->
	</select>

添加属性后就ok了

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	<!--     动态sql -->
	<select id="selectStateUserName" resultType="User" parameterType="string">
			select * from user 
			where state=1
		<if test="value !=null and value != ''">
		 	AND name like '%${value}%'
		</if> 
		
<!-- 		<if test="value !=null and value != ''"> -->
<!-- 		 	AND name like #{name} -->
<!-- 		</if>  -->
	</select>

经过了解Mybatis开发以下几点规范：

1、在mapper.xml中namespace等于mapper接口地址

2、mapper.java接口中的方法名和mapper.xml中statement的id一致

3、mapper.java接口中的方法输入参数类型和mapper.xml中statement的parameterType指定的类型一致。

4、mapper.java接口中的方法返回值类型和mapper.xml中statement的resultType指定的类型一致。