【问题现象】

在使用Mybatis的过程中，如果使用注解方式，同时使用到了script的foreach来操作list参数，如图：

@Select({"<script>",
            "select * from report where deleteflag=0 and id in ",
            "<foreach collection=\"ids\" item=\"id\" index=\"index\" open=\"(\" separator=\",\" close=\")\">",
            "#{id}",
            "</foreach>",
            "</script>"})
    public List<ReportEntity> getEntitiesByIds(List<Long> ids);

运行时会出现如下报错：

org.apache.ibatis.binding.BindingException: Parameter 'ids' not found. Available parameters are [collection, list]
	at org.apache.ibatis.session.defaults.DefaultSqlSession$StrictMap.get(DefaultSqlSession.java:343) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.scripting.xmltags.DynamicContext$ContextAccessor.getProperty(DynamicContext.java:115) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.ognl.OgnlRuntime.getProperty(OgnlRuntime.java:2685) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.ognl.ASTProperty.getValueBody(ASTProperty.java:114) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.ognl.SimpleNode.getValue(SimpleNode.java:258) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.ognl.Ognl.getValue(Ognl.java:470) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.ognl.Ognl.getValue(Ognl.java:434) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.scripting.xmltags.OgnlCache.getValue(OgnlCache.java:44) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.scripting.xmltags.ExpressionEvaluator.evaluateIterable(ExpressionEvaluator.java:43) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.scripting.xmltags.ForEachSqlNode.apply(ForEachSqlNode.java:55) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.scripting.xmltags.MixedSqlNode.apply(MixedSqlNode.java:33) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.scripting.xmltags.DynamicSqlSource.getBoundSql(DynamicSqlSource.java:41) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.mapping.MappedStatement.getBoundSql(MappedStatement.java:292) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:81) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141) ~[mybatis-3.4.6.jar:3.4.6]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_271]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_271]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_271]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_271]
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433) ~[mybatis-spring-1.3.2.jar:1.3.2]
	at com.sun.proxy.$Proxy59.selectList(Unknown Source) ~[na:na]
	at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:230) ~[mybatis-spring-1.3.2.jar:1.3.2]
	at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:139) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:76) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59) ~[mybatis-3.4.6.jar:3.4.6]
	at com.sun.proxy.$Proxy62.getEntitiesByIds(Unknown Source) ~[na:na]
	at com.kid.topten.main.service.ReportService.queryReportByHot(ReportService.java:31) ~[classes/:na]
	at com.kid.topten.main.controller.MainController.getHotReportList(MainController.java:34) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_271]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_271]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_271]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_271]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.22.jar:5.3.22]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.22.jar:5.3.22]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1070) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:655) ~[tomcat-embed-core-9.0.65.jar:4.0.FR]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.22.jar:5.3.22]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) ~[tomcat-embed-core-9.0.65.jar:4.0.FR]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.22.jar:5.3.22]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.22.jar:5.3.22]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.22.jar:5.3.22]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.22.jar:5.3.22]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.22.jar:5.3.22]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.22.jar:5.3.22]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1789) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.65.jar:9.0.65]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_271]

【原因】

在Mybatis中，当传入的参数只有一个，且为List时，它会自动封装一层Map，Map中的 key会自动用list，value就是你传入的List参数，所以直接通过参数名“ids”等将获取不会到对应参数，而应该使用他的key ：“list”进行获取，如图：

{
	"list":
	[
		{},{},{}
	]
}

如果参数多于一个，则不会出现该问题。

【解决】

解决方案一

最容易的解决办法，就是增加平铺的参数，让参数数量大于一个，例如一个list参数，一个string，这样就可以直接使用对应的参数名了，如图：

在这里插入图片描述

解决方案二

第二种比较容易的解决办法，就是获取参数时，通过“list”获取，如图：

@Select({"<script>",
            "select * from report where deleteflag=0 and id in ",
            "<foreach collection=\"list\" item=\"id\" index=\"index\" open=\"(\" separator=\",\" close=\")\">",
            "#{id}",
            "</foreach>",
            "</script>"})
    public List<ReportEntity> getEntitiesByIds(List<Long> ids);
解决方案三

当然还有其他解决办法，将该参数自己封装一层结构体，这样就可以通过对应的参数名来获取了：

@Select({"<script>",
            "select * from report where deleteflag=0 and id in ",
            "<foreach collection=\"ids\" item=\"id\" index=\"index\" open=\"(\" separator=\",\" close=\")\">",
            "#{id}",
            "</foreach>",
            "</script>"})
    public List<ReportEntity> getEntitiesByIds(Params param);

其中，封装的Params类如下，其中ids作为它的属性存在，这样就可以通过“ids”进行获取：

public class Params {

    private List<Long> ids;

}
# mybatis # list # java # 数据库 # sql
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