问题背景:
在Dao中使用MyBatis进行查询操作,参数是传的一个List:studentNameList,但是在执行查询的时候报错,具体日志如下:
- com.chenzhou.base.mybatis.IbatisSystemException: SqlSession operation; nested exception is org.apache.ibatis.exceptions.PersistenceException:
- ### Error querying database. Cause: org.apache.ibatis.binding.BindingException: Parameter ‘studentNameList’ not found. Available parameters are [list]
- ### Cause: org.apache.ibatis.binding.BindingException: Parameter ‘studentNameList’ not found. Available parameters are [list]
- at com.chenzhou.base.mybatis.SqlSessionTemplate.wrapException(SqlSessionTemplate.java:341)
- at com.chenzhou.base.mybatis.SqlSessionTemplate.execute(SqlSessionTemplate.java:127)
- at com.chenzhou.base.mybatis.SqlSessionTemplate.execute(SqlSessionTemplate.java:106)
- at com.chenzhou.base.mybatis.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:138)
- at com.chenzhou.dao.GenericMybatisDao.count(GenericMybatisDao.java:306)
- at com.chenzhou.cds.ps.dao.impl.StudentDao.getStudentCount(StudentDao.java:42)
- at com.chenzhou.cds.ps.dao.impl.StudentDao$$FastClassByCGLIB$$8819e766.invoke(<generated>)
- at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:191)
- at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:689)
- at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
- at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
- at com.chenzhou.util.LogUtil.doMethodInfo(LogUtil.java:85)
- at com.chenzhou.util.LogUtil.doDebugMethodLog(LogUtil.java:36)
- at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
- at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
- at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
- at java.lang.reflect.Method.invoke(Method.java:597)
- at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
- at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
- at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
- at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
- at org.springframework.aop.aspectj.AspectJAfterThrowingAdvice.invoke(AspectJAfterThrowingAdvice.java:55)
- at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
- at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
- at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
- at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:90)
- at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
- at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:622)
- at com.chenzhou.cds.ps.dao.impl.StudentDao$$EnhancerByCGLIB$$d4fcf513.getStudentCount(<generated>)
- at com.chenzhou.ps.dao.StudentDaoTest.testgetStudentCount(StudentDaoTest.java:44)
- ……
单元测试用例代码如下:
- @Test
- public void testgetStudentCount(){
- List<String> studentNameList = new ArrayList<String>();
- studentNameList.add(“chenzhou”);
- studentNameList.add(“zhangsan”);
- studentNameList.add(“lisi”);
- int count = studentDao.getStudentCount(studentNameList);
- System.out.println(count);
- }
studentDao中的getStudentCount方法代码如下:
- public int getStudentCount(List<String> studentNameList){
- return super.count(“getStudentCount”, studentNameList);
- }
MyBatis mapper.xml定义如下:
- <!– 查询学生数量 –>
- <select id=“Student.getStudentCount” parameterType=“java.util.List” resultType=“java.lang.Integer”>
- <![CDATA[
- SELECT
- COUNT(*)
- FROM
- t_student WHERE 1=1
- ]]>
- <if test=“studentNameList != null”>
- AND student_name in
- <foreach collection=“studentNameList” item=“item” open=“(“ separator=“,” close=“)”>
- #{item}
- </foreach>
- </if>
- </select>
根据报错日志分析,是MyBatis在解析xml时找不到其中声明的studentNameList,但是在Dao中明明传的参数就是studentNameList,怎么会报错呢?
查询了一下MyBatis官方的说明文档,终于找到了原因,在http://mybatis.github.io/mybatis-3/zh/dynamic-sql.html#foreach里有一段说明:
写道
注意 你可以传递一个 List 实例或者数组作为参数对象传给 MyBatis。当你这么做的时 候,MyBatis 会自动将它包装在一个 Map 中,用名称在作为键。List 实例将会以“list” 作为键,而数组实例将会以“array”作为键。
因为我传的参数只有一个,而且传入的是一个List集合,所以mybatis会自动封装成Map<“list”,studentNameList>。在解析的时候会通过“list”作为Map的key值去寻找。但是我在xml中却声明成studentNameList了,所以自然会报错找不到。
解决办法:
第一种就是修改mapper.xml中foreach标签内容,把studentNameList修改为list
- <if test=“list != null”>
- AND student_name in
- <foreach collection=“list” item=“item” open=“(“ separator=“,” close=“)”>
- #{item}
- </foreach>
- </if>
不过这种方式我个人不太建议,因为以后如果要扩展该方法,增加集合参数的时候,还得修改xml中的内容。
第二种方式,修改dao中的参数传入方式,手动封装成map,然后把map当参数传进去
Dao方法修改为:
- public int getStudentCount(List<String> studentNameList){
- //把参数手动封装在Map中
- Map<String, Object> map = new HashMap<String, Object>();
- map.put(“studentNameList”, studentNameList);
- return super.count(“getStudentCount”, map);
- }
然后修改mapper.xml中的parameterType类型为Map
- <!–注意下面的parameterType类型必须修改为Map类型,foreach中引用的List名称不用改变–>
- <select id=“Student.getStudentCount” parameterType=“java.util.Map” resultType=“java.lang.Integer”>
- <![CDATA[
- SELECT
- COUNT(*)
- FROM
- t_student WHERE 1=1
- ]]>
- <if test=“studentNameList != null”>
- AND student_name in
- <foreach collection=“studentNameList” item=“item” open=“(“ separator=“,” close=“)”>
- #{item}
- </foreach>
- </if>
- </select>
修改完后,重新执行了一下测试用例,测试通过。