mybatis mapper namespace

http://www.mybatis.org/mybatis-3/zh/sqlmap-xml.html#insert_update_and_delete

org.apache.ibatis.exceptions.PersistenceException:
### Error querying database.  Cause: org.apache.ibatis.executor.ExecutorException: No constructor found in tk.mybatis.springboot.model.Course matching [java.lang.Integer, java.lang.String]
### The error may exist in mapper/CourseMapper.xml
### The error may involve tk.mybatis.springboot.mapper.CourseMapper.selectAll
### The error occurred while handling results
### SQL: select * from course
### Cause: org.apache.ibatis.executor.ExecutorException: No constructor found in tk.mybatis.springboot.model.Course matching [java.lang.Integer, java.lang.String]
    at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:122)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:113)
    at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:122)
    at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:64)
    at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53)
    at com.sun.proxy.$Proxy6.selectAll(Unknown Source)

org.apache.ibatis.jdbc.RuntimeSqlException: Error executing: create TABLE course (
id INTEGER ,
NAME VARCHAR(20)
)
.  Cause: org.apache.ibatis.jdbc.RuntimeSqlException: Line missing end-of-line terminator (;) => create TABLE course (
id INTEGER ,
NAME VARCHAR(20)
)

    at org.apache.ibatis.jdbc.ScriptRunner.executeLineByLine(ScriptRunner.java:141)
    at org.apache.ibatis.jdbc.ScriptRunner.runScript(ScriptRunner.java:101)

org.apache.ibatis.binding.BindingException: Type interface tk.mybatis.springboot.mapper.CourseMapper is not known to the MapperRegistry.
    at org.apache.ibatis.binding.MapperRegistry.getMapper(MapperRegistry.java:47)
    at org.apache.ibatis.session.Configuration.getMapper(Configuration.java:689)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.getMapper(DefaultSqlSession.java:250)

mybatis中定义行为的接口，需要在xml文件中注册：

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="tk.mybatis.springboot.mapper.CourseMapper">

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：

1. com.chenzhou.base.mybatis.IbatisSystemException: SqlSession operation; nested exception is org.apache.ibatis.exceptions.PersistenceException:
2. ### Error querying database. Cause: org.apache.ibatis.binding.BindingException: Parameter 'studentNameList' not found. Available parameters are [list]
3. ### Cause: org.apache.ibatis.binding.BindingException: Parameter 'studentNameList' not found. Available parameters are [list]
4. at com.chenzhou.base.mybatis.SqlSessionTemplate.wrapException(SqlSessionTemplate.java:341)
5. at com.chenzhou.base.mybatis.SqlSessionTemplate.execute(SqlSessionTemplate.java:127)
6. at com.chenzhou.base.mybatis.SqlSessionTemplate.execute(SqlSessionTemplate.java:106)
7. at com.chenzhou.base.mybatis.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:138)
8. at com.chenzhou.dao.GenericMybatisDao.count(GenericMybatisDao.java:306)
9. at com.chenzhou.cds.ps.dao.impl.StudentDao.getStudentCount(StudentDao.java:42)
10. at com.chenzhou.cds.ps.dao.impl.StudentDao$$FastClassByCGLIB$$8819e766.invoke(<generated>)
11. at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:191)
12. at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:689)
13. at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
14. at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
15. at com.chenzhou.util.LogUtil.doMethodInfo(LogUtil.java:85)
16. at com.chenzhou.util.LogUtil.doDebugMethodLog(LogUtil.java:36)
17. at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
18. at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
19. at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
20. at java.lang.reflect.Method.invoke(Method.java:597)
21. at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
22. at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
23. at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
24. at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
25. at org.springframework.aop.aspectj.AspectJAfterThrowingAdvice.invoke(AspectJAfterThrowingAdvice.java:55)
26. at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
27. at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
28. at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
29. at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:90)
30. at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
31. at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:622)
32. at com.chenzhou.cds.ps.dao.impl.StudentDao$$EnhancerByCGLIB$$d4fcf513.getStudentCount(<generated>)
33. at com.chenzhou.ps.dao.StudentDaoTest.testgetStudentCount(StudentDaoTest.java:44)
34. ……

单元测试用例代码如下：

1. @Test
2. public void testgetStudentCount(){
3. List<String> studentNameList = new ArrayList<String>();
4. studentNameList.add("chenzhou");
5. studentNameList.add("zhangsan");
6. studentNameList.add("lisi");
7. int count = studentDao.getStudentCount(studentNameList);
8. System.out.println(count);
9. }

studentDao中的getStudentCount方法代码如下：

1. public int getStudentCount(List<String> studentNameList){
2. return super.count("getStudentCount", studentNameList);
3. }

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。

http://www.cnblogs.com/winkey4986/p/3480328.html