MyBatis批量操作報錯：Parameter 'xxxList' not found. Available parameters are [list]

問題背景：

在Dao中使用MyBatis進行查詢操作，參數是傳的一個List：studentNameList，但是在執行查詢的時候報錯，具體日誌如下：

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)
……

單元測試用例代碼如下：

@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方法代碼如下：

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

MyBatis mapper.xml定義如下：

<!-- 查詢學生數量  -->
<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>

根據報錯日誌分析，是MyBatis在解析xml時找不到其中聲明的studentNameList，但是在Dao中明明傳的參數就是studentNameList，怎麼會報錯呢?

查詢了一下MyBatis官方的說明文檔，終於找到了原因，在http://mybatis.github.io/mybatis-3/zh/dynamic-sql.html#foreach裏有一段說明：

寫道

注意 你可以傳遞一個 List 實例或者數組作爲參數對象傳給 MyBatis。當你這麼做的時 候,MyBatis 會自動將它包裝在一個 Map 中,用名稱在作爲鍵。List 實例將會以“list” 作爲鍵,而數組實例將會以“array”作爲鍵。

因爲我傳的參數只有一個，而且傳入的是一個List集合，所以mybatis會自動封裝成Map<"list",studentNameList>。在解析的時候會通過“list”作爲Map的key值去尋找。但是我在xml中卻聲明成studentNameList了，所以自然會報錯找不到。

 

解決辦法：

第一種就是修改mapper.xml中foreach標籤內容，把studentNameList修改爲list

<if test="list != null">
	AND student_name in
	<foreach collection="list" item="item" open="(" separator="," close=")">
		#{item} 
	</foreach>
</if>

不過這種方式我個人不太建議，因爲以後如果要擴展該方法，增加集合參數的時候，還得修改xml中的內容。

 

第二種方式，修改dao中的參數傳入方式，手動封裝成map，然後把map當參數傳進去

Dao方法修改爲：

public int getStudentCount(List<String> studentNameList){
	//把參數手動封裝在Map中
	Map<String, Object> map = new HashMap<String, Object>();
	map.put("studentNameList", studentNameList);
	return super.count("getStudentCount", map);
}

然後修改mapper.xml中的parameterType類型爲Map

<!--注意下面的parameterType類型必須修改爲Map類型,foreach中引用的List名稱不用改變-->
<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>

修改完後，重新執行了一下測試用例，測試通過。