Mybatis报错—— Mapped Statements collection does not contain value for com.mapper.DepartmentMapper

Mybatis报错—— Mapped Statements collection does not contain value for com.mapper.DepartmentMapper.getDeptById

前言：
如果用getMapper()或其他方法，直接获取Mapper接口时，对应的映射文件没有在全局配置文件中注册，报错比较简单（EmployeeMapperPlus is not known to the MapperRegistry），今天关联查询时报了一个异常，也是映射文件没在全局配置文件中注册，报错不太一样，关键是这段：

### Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.mapper.DepartmentMapper.getDeptById

报错如下：

org.apache.ibatis.exceptions.PersistenceException: ### Error querying database.  Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.mapper.DepartmentMapper.getDeptById### The error may exist in com/mapper/EmployeeMapperPlus.xml### The error may involve com.mapper.EmployeeMapperPlus.getEmpByIdStep### The error occurred while handling results### SQL: select * from tbl_employee where id = ?### Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.mapper.DepartmentMapper.getDeptById    at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150)    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)    ... 29 more

代码如下：

<!-- 使用association进行分步查询     1.先按照员工id查询员工信息    2.根据查询员工信息中的d_id值去部门表查出部门信息    3.部门设置到员工中：-->    <resultMap type="com.bean.Employee" id="MyEmpByStep">        <id column="id" property="id" />        <result column="last_name" property="lastName" />        <result column="gender" property="gender"/>        <result column="email" property="email"/>        <!-- association定义关联的封装规则                select:表明当前属性是调用select指定的方法查出的结果                        全类名+方法名;                column：指定将哪一列的值传给这个方法                流程：使用select指定的方法（传入column指定的这列参数的值）查出对象，并封装给property指定的属性        -->        <association             property="dept"             select="com.mapper.DepartmentMapper.getDeptById"            column="d_id">        </association>    </resultMap>

错误原因：
在使用<association>标签进行关联分步查询时，select属性中DepartmentMapper接口所对应的映射文件，没有在全局配置文件中配置，如下：

<association             property="dept"             select="com.mapper.DepartmentMapper.getDeptById"            column="d_id"></association>

所以报错 Mapped Statements collection does not contain value for com.mapper.DepartmentMapper.getDeptById，就是说映射声明集合中不包含com.mapper.DepartmentMapper.getDeptById（select的值，集它指向的方法）

问题解决：
只要在全局配置文件中配置对应的映射文件即可，代码如下：

<mappers>    <mapper resource="com/mapper/DepartmentMapper.xml" /></mappers>

补充：
如果用getMapper()或其他方法，直接获取Mapper接口时，对应的映射文件没有注册，报错比较简单（EmployeeMapperPlus is not known to the MapperRegistry），代码和报错信息如下：

代码：
EmployeeMapperPlus Mapper =
openSession.getMapper(EmployeeMapperPlus.class);

报错信息： org.apache.ibatis.binding.BindingException: Type interface com.mapper.EmployeeMapperPlus is not known to the
MapperRegistry.