A query was run and no Result Maps were found for...原来是mapper.xml文件出了问题,是使用MyBatis最常见的一种错误

今天遇到一个问题，原来是mapper.xml文件出了问题,是使用MyBatis最常见的一种错误

报错的结果是这样的：

 A query was run and no Result Maps were found for the Mapped Statement 'cn.zrgk.dao.RoleMapper.getRoleList'.  

　　It's likely that neither a Result Type nor a Result Map was specified.
	

org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'cn.zrgk.dao.RoleMapper.getRoleList'. 
　　 It's likely that neither a Result Type nor a Result Map was specified.
    org.apache.ibatis.executor.resultset.FastResultSetHandler.validateResultMapsCount(FastResultSetHandler.java:177)
    org.apache.ibatis.executor.resultset.FastResultSetHandler.handleResultSets(FastResultSetHandler.java:150)
    org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:57)
    org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:70)
    org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:57)
    org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:259)
    org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:132)
    org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:105)
    org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:81)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:606)

我的mapper.xml文件中有个查询语句是这样写的：

 　　大家看看图一，好像根本没有错误，对吗？再看看

　　是的，没错，我没有指定这个方法的返回类型，系统无法识别，于是就这样改了一下，发现不报错了

所以平时啊，我们要多多注意这些细节，更要去多加理解