Error querying database. Cause: ...Mapped Statements collection does not contain value

1. 出现异常：

org.apache.ibatis.exceptions.PersistenceException:  ### Error querying database.  Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.bookStore.dao.OrderItemMapper.selectByUserName ### Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.bookStore.dao.OrderItemMapper.selectByUserName at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:23) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:107) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:98) at com.bookStore.dao.ItemMapperTest.testSelectByUserName(ItemMapperTest.java:25) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) Caused by: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.bookStore.dao.OrderItemMapper.selectByUserName at org.apache.ibatis.session.Configuration$StrictMap.get(Configuration.java:775) at org.apache.ibatis.session.Configuration.getMappedStatement(Configuration.java:615) at org.apache.ibatis.session.Configuration.getMappedStatement(Configuration.java:608) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:103) ... 26 more

2. 原因：

（1）mapper.xml中没有加入namespace

 （2）与之对应的是dao层接口 mapper.xml中的方法和接口mapper的方法不对应

 （3）与之对应的是（insert,delete,update,select）几个方法所定义id与接口里面的方法不一致 mapper.xml没有加入到mybatis-config.xml中(即总的配置文件)

（4）mapper.xml中定义的namespace与测试代码中的不一致（测试代码如下）

List<Item> list = session.selectList("com.bookStore.dao.ItemMapper.selectByUserName",order.getUserName());